Research ArticleNature and Evolution of the Ore-Forming Fluids fromNanmushu Carbonate-Hosted Zn-Pb Deposit in the MayuanDistrict Shaanxi Province Southwest China

Suo-Fei Xiong1 Yong-Jun Gong1 Shu-Zhen Yao1

Chuan-Bo Shen1 Xiang Ge1 and Shao-Yong Jiang12

1State Key Laboratory of Geological Processes and Mineral Resources Faculty of Earth Resources and Collaborative InnovationCenter for Exploration of Strategic Mineral Resources China University of Geosciences Wuhan 430074 China2State Key Laboratory for Mineral Deposits Research Department of Earth Sciences Nanjing University Nanjing 210093 China

Correspondence should be addressed to Shao-Yong Jiang shyjiangcugeducn

Received 5 May 2017 Revised 21 August 2017 Accepted 24 October 2017 Published 21 November 2017

Academic Editor Sabina S Palinkas

Copyright copy 2017 Suo-Fei Xiong et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The Nanmushu carbonate-hosted Zn-Pb deposit is located in the Mayuan district of Shaanxi Province a newly discoveredmetallogenic district next to the Sichuan Basin in the northern margin of the Yangtze Block which is the largest and the only onethat is currently mined in this district The 12057534S values of sulfides are characterized by positive values with a peak around +18permiland the reduced sulfur may have derived from reduction of SO4

2minus from paleoseawater or evaporitic sulfates that have possibly beenleached by basinal brines during mineralization stage Detailed fluid inclusion study shows two types of fluids in the sphaleritequartz dolomite calcite and barite that is aqueous-salt dominant inclusions (type I) and hydrocarbon-bearing inclusions (typeII) The Laser Raman spectroscopy study shows occurrence of certain amount of CH4 C4H6 and bitumen The salinities showsimilar values around 6 to 12wt NaCl equivalent but a decreasing temperature from early to late stages (typically 200∘ to 320∘Cin stage I 180∘ to 260∘C in stage II and 140∘ to 180∘C in stage III) These features may be related to basinal brines mixing betweenan external higher salinity CaCl2 plusmn MgCl2-rich fluid and a local H2O-NaCl methane-rich fluid

1 Introduction

Carbonate-hosted Zn-Pb deposit is one of the most impor-tant Pb and Zn producers in the world however the detailedore-forming processes are still ambiguous especially whencarbonate-hosted Zn-Pb deposit is spatially associated withorganic matter in or next to sedimentary basins The closerelationship between carbonate-hosted Zn-Pb deposits andhydrocarbon reservoirs in a sedimentary basin has beenwidely noted [1ndash4] but the detailed metallogenic mechanismremains poorly understood

The Mayuan district in the northern margin of theYangtze Block (Figure 1) next to the Sichuan Basin is anewly discovered Zn-Pb ore concentrated area with largeeconomic significance Since the discovery of these depositsin 2004 only few researches have been carried out and theore genesis remains controversial Qi et al [5] suggested a

stratabound syn-sedimentary hydrothermal origin for theseZn-Pb deposits according to geological characteristics of allorebodies hosted in theNeoproterozoic Dengying Formationdolomite Chen et al [6] claimed that the Dengying Forma-tion dolomite may have been influenced by hydrothermalfluids on account of trace elements and REEs data Otherresearchers [7ndash11] suggested that these deposits belong tothe Mississippi Valley-type (MVT) Zn-Pb deposit based onthe fluid inclusion and isotope geochemical data Previousmicrothermometry measurements show that fluid inclu-sions of hydrothermal epoch homogenized in temperaturesbetween 98 and 337∘C [8] Based onH-O-C-He-Ar-Sr isotopedata Gao et al [11] proposed that the Zn-Pb deposits in theMayuan district may have precipitated from a mixture ofcrustal fluid and meteoric water Gao et al [11] put forwarda hypothesis of organic fluid origin for ore fluids based onthe low 12057513C values (from minus360 to minus283permil for 12057513CCH4

HindawiGeofluidsVolume 2017 Article ID 2410504 19 pageshttpsdoiorg10115520172410504

2 Geofluids

LMS MCS DBS

Qinling Orogenic Belt

North China Block

Yangtze Block

Sichuan Basin

Figure 1(b)

N

200 km

104∘E 106∘E 108∘E 110∘E

34∘ N

32∘ N

30∘ N

(a)

NNanmushuLengqingpo

KongxigouJiulingzi

Jiandongzi

Deposit

Fault

South ore zone

North ore zone

Middleore zone

0 20(km)

Jinning-chengjiang intermediate-acidigneous rocks

Neoproterozoic Dengying Formation

Mesoproterozoic Huodiya Group

Jurassic-Cambrian Formations

(b)

Figure 1 (a) Tectonic location of the Mayuan district (b) The distribution of the South Middle and North ore zones and major Zn-Pbdeposits in the Mayuan district (modified fromHou et al 2007 [23]) MCS Micangshan fold-and-thrust belt LMS Longmenshan fold-and-thrust belt DBS Dabashan fold-and-thrust belt

and from minus277 to minus224permil for 12057513CC2H6 resp) of fluidinclusion in the sphalerite which are similar to the 12057513Cvalues of the gas reservoir in the Dengying Formation In thisdeposit hand specimen and microscopic-scale thin sectionsof the sulfide ores show a spatial association with bitumen[7 8 10] However the characteristics of the organic-richfluids the link between the organic-rich fluids mechanismsby which the ore-forming fluids make sphalerite and galenaprecipitated and the controlling factors of mineralization arestill ambiguous

There are three ore zones (North Middle and South)in the Mayuan district [5] Metallogenic prospecting of theNorth and Middle zones is 10Mt and 15Mt respectivelyFurther prospecting work has not started yet in the Northand Middle zones The South zone is the only one that isbeing currently mined in the Mayuan district There are aseries of occurrences of the Zn-Pb deposits in the Southzone among which the Nanmushu deposit is the largest one(Figure 1) The study of ore-forming fluid is an effective wayto trace the ore-forming process and can provide effectiveinformation about mineralization [12ndash15] In this paper theNanmushu deposit was selected for a detailed fluid inclusionstudy and our results demonstrate a carbonate-hosted Zn-Pb deposit may have formed by mixing of high salinitybrines into a local H2O-NaClmethane-rich fluid In additionhere we also present a detailed geological and sulfur isotopestudy and combined with fluid inclusion study for theNanmushu deposit it can provide a better understanding ofthe nature and origin of the ore-forming fluids and the oregenesis These results can also provide new insights into themechanisms that formed the ore deposits with hydrocarbon-bearing fluids Although this approach does not attempt to

explain all the deposit features in this district it will possiblyprovide a reasonably detailed new understanding for a typicaldeposit in the Mayuan district

2 Geological Background

21 Regional Geology The Yangtze Block is separated fromthe North China Block by the Qinling Orogenic Belt (Fig-ure 1(a)) The Yangtze Block is composed of Archean to EarlyProterozoic basements Mesoproterozoic folded basementandNeoproterozoic toMesozoic cover sequences [18ndash21]Thethick cover of Neoproterozoic to Permian strata is over 9 kmwhich comprises glacial deposits clastic metavolcanic rocksand carbonate Abundant carbonate-hosted Zn-Pb depositsare located in the northern belt of the Yangtze Block [22]

The Mayuan district is a newly discovered Zn-Pb metal-logenic district located in the northern margin of YangtzeBlock next to Sichuan Basin This district is also locatedat the junction of the Qinling Orogenic Belt to the Southof Yangtze Block and along the eastern margin of theMicangshan fold-and-thrust belt (Figure 1(a)) The MayuanZn-Pbmetallogenic district includes three ore zones namelythe South Middle and North zones (Figure 1(b)) The Southore zone extends over 20 km and broadens 20 to 120mwith approximately 21Mt Zn (with a grade of 12ndash45 wt)and 01Mt Pb (with a grade of 06ndash35 wt) This ore zonecontains five deposits including Kongxigou LengqingpoNanmushu Jiulingzi and Jiandongzi from SWW to NEE[17 23]

22 Geology of the Nanmushu Zn-PbDeposit TheNanmushuZn-Pb deposit is located in the central part of the South

Geofluids 3

Lower Cambrian Guojiaba Formationcarbonaceous slates

Mesoproterozoic HuodiyaGroup marble

Orebody and number

Attitude of stratum

Fault and number

Sampling locationGeological boundary

Angular unconformityboundary

Parallel unconformityboundary

Drill hole

ZK 001

ZK 001

Zn1

PbZn1

Zn2Zn3

Zn1

Zn4

PbZn2

PbZn3Zn5

Nanmushu

0

E

S

W

N

52∘

37∘45∘

45∘52∘

32∘

52∘

41∘

48∘

32∘

30∘

Ｈ1

1

2

1

3

4 5

500(m)

Neoproterozoic Dengying Formationchert-bearing banded dolomite (2dn2

4)

Neoproterozoic Dengying Formationbreccia dolomite (2dn2

3)

Neoproterozoic Dengying Formationlaminar dolomite (2dn2

2)Neoproterozoic Dengying Formationsandstone and dolomite (2dn2

1)

clastic rocks (2dn1)Neoproterozoic Dengying Formation

Figure 2 Geological map of the Nanmushu Zn-Pb deposit showing the orebodies are mainly hosted in the third section of NeoproterozoicDengying Formation breccia dolomite (Z21198891198992

3) (after Han et al 2016 [10])

ore zone (Figure 1(b)) In the deposit the outcropped strataconsist of Mesoproterozoic Huodiya Group NeoproterozoicDengying Formation and the Lower Cambrian GuojiabaFormation (Figure 2) The Huodiya Group is mainly com-posed of marbles pyroclastic rocks and siliceous slates andthe most common rocks of the Huodiya Group in this areaare marbles This group is unconformably overlain by theNeoproterozoic Dengying Formation carbonate rocks whichmainly include dolomites with minor amount of quartzsandstones and limestones whereas the Lower CambrianGuojiaba Formation is characterized by argillaceous lime-stones and carbonaceous slates The Dengying Formation inthe study area can be subdivided into the lower member(Z21198891198991) and the upper member (Z21198891198992

1ndash4) (Figure 2) Z21198891198991(31 to 50m thick) is characterized by clastic rocks sandstoneand conglomerate Z21198891198992

1ndash4 can be further subdivided intofour beds from the bottom upward the first bed (Z21198891198992

1 350to 450m thick) consists of off-white fine-crystalline dolomitesandstone and pebbly sandstone the second bed (Z21198891198992

240 to 80m thick) contains gray laminar algal dolomite andgray-white laminar dolomite the third bed (Z21198891198992

3 78 to120m thick) comprises banded dolomite breccia dolomiteand dolorudite which hosted major orebodies in the Nan-mushu deposit the fourth bed (Z21198891198992

4 35 to 50m thick) isdominated by chert-bearing banded dolomite

Han et al [10] described five major faults in the Nan-mushu deposit The F1 separated the Dengying Formationand the Huodiya Group with strikes 150∘ to 165∘ and dips20∘ to 50∘ The F2 separated upper member of DengyingFormation into two parts that is Z21198891198992

2 and Z211988911989923 This

fault is 8 to 15m wide with strikes 155∘ to 165∘ and dips15∘ to 55∘ The F3 is the ore-controlling fault in the miningdistrict which crosscuts the Dengying Formation dolomitesand generally parallels to F2 The F3 fault is a thrust fault withstrikes 150∘ to 165∘ and dips 25∘ to 55∘ This fault is marked bya 3 to 30m wide fracture and breccia zone which probablyacted as conduits for ore-forming hydrothermal fluids andclosely related to the mineralization The F4 and F5 are post-ore faults that cut the orebodies

In the Nanmushu deposit there are five zinc orebodiesand three lead-zinc orebodies (Figure 2 Table 1) Five zincorebodies occur within Z21198891198992

3 of Dengying Formation ofwhich single orebody is 100ndash2560m in length and 05ndash325min thickness with zinc grades at 13ndash131 wtThree lead-zincorebodies are 86ndash160m in length and 08ndash84m in thicknesswith zinc grades at 11ndash64 wt and 09ndash33 wt respectively(Table 1)

Mineralization throughout the Nanmshu Zn-Pb depositis characterized by open space filling and occurs as brecciasveins stockworks and massive ores which appear to be

4 Geofluids

Table 1 Main characteristics of orebodies in the Nanmushu Zn-Pb deposit

Number Length (m) Thickness (m) Zn grade (wt) Pb grade (wt)Range Average Range Average Range Average

Zn1 2560 15sim325 76 15sim114 45Zn2 180 10sim53 28 13sim34 25Zn3 260 05sim64 21 27sim131 41Zn4 106 13 13 14 14Zn5 100 17sim25 21 17sim19 18PbZn1 86 16 16 19 19 24 24PbZn2 160 08sim84 46 11sim32 30 09 09PbZn3 160 58 58 11sim64 53 33 33

controlled by the third bed of the Dengying Formation(Z21198891198992

3) It can be considered that the cavity filling wasformed mainly by hydrothermal mineralization Hou et al[19 20] described the Zn1 as amajor ore shoot which extends2560m and broadens 15ndash325m (average thickness at 76m)with zinc grade at 15ndash114 wt (average value at 45 wt)(Table 1) with the ore shoot occupying a dilational flexurein the 1030m height (Figure 3) Hydrothermal alterationin the Nanmushu Zn-Pb deposit comprising silicificationand carbonate alteration is not extensive and it is notclosely related to mineralization The shapes of orebodies arestratiform-like lenticular and vein and majority of themare strata-bounded and controlled by the bedding-parallelfractures

3 Samples and Analytical Methods

Samples were collected from the Nanmushu Zn-Pb depositin the open pit at elevations of 1030m 1070m and 1170mrespectively Polished blocks and thin sections were initiallyexamined by reflected and transmitted light microscopy tocharacterize the mineralogy textures and parageneses

Twenty-nine doubly polished-thin sections (100120583mthick) of quartz dolomite barite calcite and sphalerite wereprepared from representative samples of the three hydro-thermal mineralization stages (I II and III) Petrographicexamination of fluid inclusions was conducted using a NikonE80I microscope with an ultraviolet (UV) attachment usingmedium-width bandpass excitation filters (330ndash380 nm)Oil-bearing fluid inclusions were identified by their fluores-cence under UV excitation Microthermometric measure-ments were conducted using a LinkhamTHMS-600Heating-Freezing Systems (from minus196∘ to 550∘C) equipped with aNikon E80I microscope at China University of GeosciencesWuhan China Thermocouples were calibrated at minus566∘C00∘C and 374∘C using synthetic FIs supplied by FLUID INCThe heatingfreezing rate is generally 02∘ to 5∘Cmin but itwas reduced to lt02∘Cmin near the phase transformationThe uncertainties for the measurements are plusmn05∘ plusmn02∘ andplusmn2∘C for runs in the range of minus120∘ to minus70∘C minus70∘ to +100∘Cand +100∘ to +600∘C respectively Ice-melting temperatureswere observed at a heating rate of less than 01∘Cmin andhomogenization temperatures at rate of le1∘Cmin

Fluid inclusions were carefully observed to identify theirgenetic and compositional types vapor-liquid ratios spatialclustering and the species The fluid inclusion petrographicstudywas based on the concept of fluid inclusion assemblages(FIAs) as described byGoldstein [24] an approach that placesfluid inclusions into assemblages that have been trappedpenecontemporaneously Fluid inclusion data was collectedfrom both primary and pseudosecondary fluid inclusionassemblages representing fluids trapped during crystalgrowth Then microthermometric data was analyzed fromtwo-three inclusions in each FIA Phase changes in every FIAgenerally occurred over 1∘ndash5∘C consistent with petrographicobservations that inclusions did not undergo postentrapmentmodification [25] Microthermometric analyses were carriedout on 258 FIAs and the results are summarized in Table 2

After careful examination of their petrography ninedoubly polished-thin sections that have adequate primaryfluid inclusions were chosen for Laser Raman spectroscopicanalysis (LRSA) LRSA was conducted at the State KeyLaboratory of Geological Processes and Mineral Resources(GPMR) China University of Geosciences Wuhan ChinaIn order to confirm the volatile species of FIs representativesamples were carried out with a Renishaw 1000 Ramanmicrospectrometer according to the method of Burke [26]Spectrograph aperture was chosen as 25120583m or 50 120583m pin-hole The spectra were recorded with counting time of 20 sto 40 s and they ranged from 50 to 3800 cmminus1

Six sphalerite samples from the main economic ore-forming stage II for conventional sulfur isotopic analyseswere collected from different localities including 1030min height 1070m in height and 1170m in height of theNanmushu zinc-lead deposit (Table 3) Conventional sulfurisotope analyses of the six samples were carried out atWuhanInstitute of Geology and Mineral Resources China Geologi-cal SurveyThese samples were first broken into 025ndash05mmfragments handpicked to gt95 purity under a binocularmicroscope and cleaned ultrasonically then crushed to lt200mesh and heated under vacuum condition with Cu2OThe SO2 gas was generated by the oxidation reaction andsulfur isotopic compositions are measured on a MAT-251 gasmass spectrometer The results are reported as 12057534S valueswith an analytical uncertainty of 02permil (2120590) Sulfur isotopiccompositions are reported in comparison with V-CDT

Geofluids 5

F

Footrill

Tunnel entrance

Fault

Zn1

Zn2

Zn1

FF

Zn3

Orebody and number

0

Ｈ1

1000(m)

Neoproterozoic Dengying Formation chert-bearing band dolomite (2dn24)

Neoproterozoic Dengying Formation breccia dolomite (2dn23)

Neoproterozoic Dengying Formation laminar dolomite (2dn22)

(a)

ZK 001

Zn1

0

340∘ 160∘

100(m)

1100

(m)

1000

Fcarbonaceous slatesLower Cambrian Guojiaba Formation

ZK 001Height

Fault

Drill hole

Geologicalboundary

Orebody and numberＨ1

1000 m

900

800

Neoproterozoic Dengying Formationchert-bearing band dolomite (2dn2

4)

Neoproterozoic Dengying Formationbreccia dolomite (2dn2

3)

Neoproterozoic Dengying Formation

laminar dolomite (2dn22)

F

(b)

Figure 3 (a) Representative simplified geologic map showing the occurrence and morphology of major orebody Zn1 at 1030m above sealevel in the Nanmushu Zn-Pb deposit (after Li et al 2007 [9]) (b) Cross-section of the Nanmushu Zn-Pb deposit (modified from Hou et al2007 [23])

4 Results

41 Paragenetic Mineralization Stages According to themin-eral assemblages and the cross-cutting relationships of theorebodies three mineralization stages are identified includ-ing the sedimentary diagenetic stage the hydrothermalore-forming stage and the post-ore supergene stage Inthe sedimentary diagenetic stage vein-type bitumen occursparallel to the country rock beddings or fractures and faraway from the orebodies (Figure 4(a)) The fine-grainedeuhedral pyrite Py(s) of this stage is 10 to 50 120583m in sizeand is disseminated within dolomite with the hydrothermal

minerals filling interspace (Figure 4(b)) The hydrothermalore-forming stage can be subdivided into three substages

Stage I Stage I characterized by the assemblage of dolomite+ quartz + pyrite + sphalerite + pyrrhotite without galena(Figure 4(c)) This type mineral assemblage usually fillsbreccias and open spaces with sphalerite impregnationIn this stage medium-grained pyrite Py(a) and medium-grained sphalerite Sp(a) vary in size ranging from 30 to100 120583m and 30 to 200120583m in diameter respectively Minorinclusions of pyrrhotite are common within the euhedralPy(a)

6 Geofluids

Table2Asummaryof

fluid

inclu

siondataforthe

Nanmushu

Zn-Pbdepo

sit

StageI

StageII

StageIII

Hostm

ineral

QSp(a)

QDol

Sp(b)

Cal

Brt

QFIssize(120583m)

3sim18

6sim11

6sim40

4sim20

4sim20

3sim14

4sim16

4sim8

Vapo

r(vol

)5sim

305sim

305sim

405sim

2010sim40

5sim25

5sim30

5sim20

Cou

ntso

fFIAs

617

3434

3043

2128

119879m(∘ C

)oftypeI

inclu

sions

minus313simminus207

minus587

minus347simminus213

ndash516

ndash513

ndash208

119879mH

H(∘ C

)oftypeI

inclu

sions

minus272simminus213

ndash370

119879ice(∘ C

)oftypeI

inclu

sions

minus94simminus24

minus76simminus38minus103simminus28minus83simminus12

minus94simminus36

minus119simminus28minus154simminus18

minus69simminus12

119879h(∘ C

)oftypeI

inclu

sions

(mean)

171sim340

225sim

314

186sim

264

152sim

265

183sim

276

107sim

202

123sim

187

149sim

195

Meanof119879h(∘ C

)239

283

223

205

238

152

165

166

Salin

ity(w

tNaC

lequ

ivalent)

43sim

133

62sim

112

47sim

143

20sim

122

59sim

133

30sim

159

31sim190

21sim104

Salin

ity(w

tNaC

l+Ca

Cl2equivalent)

66sim

116

116sim148

Bulkdensity

(gcm3)

073sim096

075sim092

085sim098

084sim098

084sim095

092sim10

3091sim10

4090sim099

Hom

ogenizationsty

leL+Vrarr

LL+Vrarr

LL+Vrarr

LLaserR

aman

spectro

scop

icanalysisof

compo

sition

H2OC

H4

H2OC

H4B

itumen

H2OC

H4C4H6B

itumen

Dom

inantaqu

eous-saltspecies

H2O-N

aCl

H2O-N

aCl-C

aCl 2plusmnMgC

l 2H2O-N

aCl-C

aCl 2plusmnMgC

l 2119879mfirstm

eltingtemperature119879

mH

Hm

eltingtemperature

ofhydroh

alite119879

icemeltingtemperature

offin

alice119879htotalh

omogenizationtemperatureB

rtbariteC

alcalciteD

oldolom

iteQ

quartzSp(a)fin

e-grainedsphaleritefrom

hydrotherm

alsta

geISp(b)coarse-grained

sphaleritefrom

hydrotherm

alstageIINo

tesSalin

ity(w

tNaC

lequ

ivalent)estim

ated

byfin

alicem

eltingtem

perature(119879

ice)oftype

Iinclusio

ns(Bod

nar1993)[13]Salin

ity(w

tNaC

l+Ca

Cl2equivalent)e

stimated

by119879m119879

mH

Hand119879iceof

type

Iinclusio

nsby

usingtheSoftw

arePackageFluids

(Steele

-MacInnise

tal2010)[16]Bu

lkdensity

oftype

Iinclu

sions

estim

ated

usingthee

quations

ofBo

dnar

(1993)[13]Dom

inantaqu

eous-saltspecies

concludedon

theb

asisof119879mandthem

icrothermom

etry

behavior

offlu

idinclu

sions

Geofluids 7

Table 3 Sulfur isotopic data of sulfides and sulfate from the Mayuan district

Sample ID Location Mineral 12057534S (permil) Data sourceNMS-1170-14 Nanmushu Sphalerite +183 This studyNMS-1030-2 Nanmushu Sphalerite +174 This studyNMS-1170-13 Nanmushu Sphalerite +180 This studyNMS-1070-13 Nanmushu Sphalerite +176 This studyNMS-1030-3 Nanmushu Sphalerite +174 This studyNMS-1070-2 Nanmushu Sphalerite +178 This studyMAYN-1 Nanmushu Sphalerite +189 Li et al 2007 [9]MAYN-2 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-3 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-4 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-5 Nanmushu Sphalerite +181 Li et al 2007 [9]MAYN-6 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-7 Nanmushu Sphalerite +194 Li et al 2007 [9]MY-8 Nanmushu Sphalerite +170 Wang et al 2008 [7]S-1 Nanmushu Sphalerite +178 Wang et al 2008 [7]S-2 Nanmushu Sphalerite +180 Wang et al 2008 [7]MWT1 Nanmushu Sphalerite +182 Hou et al 2007 [17]MWT3 Nanmushu Sphalerite +179 Hou et al 2007 [17]H-1 Nanmushu Pyrite +188 Wang et al 2008 [7]H-2 Nanmushu Pyrite +186 Wang et al 2008 [7]F-1 Nanmushu Galena +168 Wang et al 2008 [7]F-2 Nanmushu Galena +166 Wang et al 2008 [7]F-3 Nanmushu Galena +156 Wang et al 2008 [7]MWT2 Nanmushu Barite +322 Hou et al 2007 [17]MWT5-1 Zhujiahe Barite +333 Hou et al 2007 [17]MWT5-2 Zhujiahe Barite +335 Hou et al 2007 [17]KXG-9 Kongxigou Sphalerite +160 Wang et al 2008 [7]MWT4 Nanrsquoanshan Galena +129 Hou et al 2007 [17]Note Nanmushu and Kongxigou deposits are from South ore zone of Mayuan district and Zhujiahe and Nanrsquoanshan are ore deposits (spots) fromMiddle orezone of Mayuan district

Stage II Stage II is dominated by the widespread coarse-grained sphalerite Sp(b) and galena as well as minor amountof coarse-grained pyrite Py(b) Zn-Pbmineralization starts atstage I and continues with sphalerite impregnation followedby galena + sphalerite impregnation which subordinate stageII The cross-cutting relationships of stage I and stage II areobserved and shown in Figure 4(d) Stage II is themajormin-eralization stage for zinc and leadThismineralization stage ismost important in terms of tonnage andmining Major typesof ores include breccia-type vein-type (Figure 4(d)) andhigh-grade massive sulfide type (Figure 4(e)) with a simplemineralogy dominated by sphalerite galena and pyrite inthis stage Bitumen Bit(a) can also be observed in this stage(Figure 4(f)) occurring in vein-type and breccia-type oresand usually associating with contemporary sphalerite andgalena and gangue minerals such as dolomite calcite andquartz The Py(b) in this stage surrounded the Sp(b) orfilled the fractures of Sp(b) and galena grains (Figure 4(g))indicating a relatively late timing of formation

Stage III Stage III marked the end of hydrothermal ore-forming epoch and was characterized by quartz + barite +

calcite + bitumen Abundant bitumens Bit(b) in this stageare emulsion drops filling the open interspace between othergangue minerals and concentrated along crystal interface ofgangue minerals as well as microfissuring or pores (Figures4(h) and 4(i)) implying the bitumen might have formed alittle later than the gangue minerals

In the supergene stage oxide minerals include smith-sonite cerusite and limonite A paragenetic sequence forminerals in the Nanmushu Zn-Pb deposit is summarized inFigure 5

42 Fluid Inclusions Petrography and Laser Raman Spec-troscopic Analysis Samples of sphalerite (Sp(a) and Sp(b))dolomite quartz calcite and barite were selected from threehydrothermal stages in the Nanmushu deposit to determinethe nature of the fluids associated with mineralizationAbundant primary pseudosecondary and secondary FIsin these minerals are found In order to avoid erroneousinterpretations secondary FIs andor FIs which partiallydecrepitate during the microthermometric processes werenot documented during experiment FIs were studied insamples that are characterized with absence of plentiful

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 3

Lower Cambrian Guojiaba Formationcarbonaceous slates

Mesoproterozoic HuodiyaGroup marble

Orebody and number

Attitude of stratum

Fault and number

Sampling locationGeological boundary

Angular unconformityboundary

Parallel unconformityboundary

Drill hole

ZK 001

ZK 001

Zn1

PbZn1

Zn2Zn3

Zn1

Zn4

PbZn2

PbZn3Zn5

Nanmushu

0

E

S

W

N

52∘

37∘45∘

45∘52∘

32∘

52∘

41∘

48∘

32∘

30∘

Ｈ1

1

2

1

3

4 5

500(m)

Neoproterozoic Dengying Formationchert-bearing banded dolomite (2dn2

4)

Neoproterozoic Dengying Formationbreccia dolomite (2dn2

3)

Neoproterozoic Dengying Formationlaminar dolomite (2dn2

2)Neoproterozoic Dengying Formationsandstone and dolomite (2dn2

1)

clastic rocks (2dn1)Neoproterozoic Dengying Formation

Figure 2 Geological map of the Nanmushu Zn-Pb deposit showing the orebodies are mainly hosted in the third section of NeoproterozoicDengying Formation breccia dolomite (Z21198891198992

3) (after Han et al 2016 [10])

ore zone (Figure 1(b)) In the deposit the outcropped strataconsist of Mesoproterozoic Huodiya Group NeoproterozoicDengying Formation and the Lower Cambrian GuojiabaFormation (Figure 2) The Huodiya Group is mainly com-posed of marbles pyroclastic rocks and siliceous slates andthe most common rocks of the Huodiya Group in this areaare marbles This group is unconformably overlain by theNeoproterozoic Dengying Formation carbonate rocks whichmainly include dolomites with minor amount of quartzsandstones and limestones whereas the Lower CambrianGuojiaba Formation is characterized by argillaceous lime-stones and carbonaceous slates The Dengying Formation inthe study area can be subdivided into the lower member(Z21198891198991) and the upper member (Z21198891198992

1ndash4) (Figure 2) Z21198891198991(31 to 50m thick) is characterized by clastic rocks sandstoneand conglomerate Z21198891198992

1ndash4 can be further subdivided intofour beds from the bottom upward the first bed (Z21198891198992

1 350to 450m thick) consists of off-white fine-crystalline dolomitesandstone and pebbly sandstone the second bed (Z21198891198992

240 to 80m thick) contains gray laminar algal dolomite andgray-white laminar dolomite the third bed (Z21198891198992

3 78 to120m thick) comprises banded dolomite breccia dolomiteand dolorudite which hosted major orebodies in the Nan-mushu deposit the fourth bed (Z21198891198992

4 35 to 50m thick) isdominated by chert-bearing banded dolomite

Han et al [10] described five major faults in the Nan-mushu deposit The F1 separated the Dengying Formationand the Huodiya Group with strikes 150∘ to 165∘ and dips20∘ to 50∘ The F2 separated upper member of DengyingFormation into two parts that is Z21198891198992

2 and Z211988911989923 This

fault is 8 to 15m wide with strikes 155∘ to 165∘ and dips15∘ to 55∘ The F3 is the ore-controlling fault in the miningdistrict which crosscuts the Dengying Formation dolomitesand generally parallels to F2 The F3 fault is a thrust fault withstrikes 150∘ to 165∘ and dips 25∘ to 55∘ This fault is marked bya 3 to 30m wide fracture and breccia zone which probablyacted as conduits for ore-forming hydrothermal fluids andclosely related to the mineralization The F4 and F5 are post-ore faults that cut the orebodies

In the Nanmushu deposit there are five zinc orebodiesand three lead-zinc orebodies (Figure 2 Table 1) Five zincorebodies occur within Z21198891198992

3 of Dengying Formation ofwhich single orebody is 100ndash2560m in length and 05ndash325min thickness with zinc grades at 13ndash131 wtThree lead-zincorebodies are 86ndash160m in length and 08ndash84m in thicknesswith zinc grades at 11ndash64 wt and 09ndash33 wt respectively(Table 1)

Mineralization throughout the Nanmshu Zn-Pb depositis characterized by open space filling and occurs as brecciasveins stockworks and massive ores which appear to be

4 Geofluids

Table 1 Main characteristics of orebodies in the Nanmushu Zn-Pb deposit

Number Length (m) Thickness (m) Zn grade (wt) Pb grade (wt)Range Average Range Average Range Average

Zn1 2560 15sim325 76 15sim114 45Zn2 180 10sim53 28 13sim34 25Zn3 260 05sim64 21 27sim131 41Zn4 106 13 13 14 14Zn5 100 17sim25 21 17sim19 18PbZn1 86 16 16 19 19 24 24PbZn2 160 08sim84 46 11sim32 30 09 09PbZn3 160 58 58 11sim64 53 33 33

controlled by the third bed of the Dengying Formation(Z21198891198992

3) It can be considered that the cavity filling wasformed mainly by hydrothermal mineralization Hou et al[19 20] described the Zn1 as amajor ore shoot which extends2560m and broadens 15ndash325m (average thickness at 76m)with zinc grade at 15ndash114 wt (average value at 45 wt)(Table 1) with the ore shoot occupying a dilational flexurein the 1030m height (Figure 3) Hydrothermal alterationin the Nanmushu Zn-Pb deposit comprising silicificationand carbonate alteration is not extensive and it is notclosely related to mineralization The shapes of orebodies arestratiform-like lenticular and vein and majority of themare strata-bounded and controlled by the bedding-parallelfractures

3 Samples and Analytical Methods

Samples were collected from the Nanmushu Zn-Pb depositin the open pit at elevations of 1030m 1070m and 1170mrespectively Polished blocks and thin sections were initiallyexamined by reflected and transmitted light microscopy tocharacterize the mineralogy textures and parageneses

Twenty-nine doubly polished-thin sections (100120583mthick) of quartz dolomite barite calcite and sphalerite wereprepared from representative samples of the three hydro-thermal mineralization stages (I II and III) Petrographicexamination of fluid inclusions was conducted using a NikonE80I microscope with an ultraviolet (UV) attachment usingmedium-width bandpass excitation filters (330ndash380 nm)Oil-bearing fluid inclusions were identified by their fluores-cence under UV excitation Microthermometric measure-ments were conducted using a LinkhamTHMS-600Heating-Freezing Systems (from minus196∘ to 550∘C) equipped with aNikon E80I microscope at China University of GeosciencesWuhan China Thermocouples were calibrated at minus566∘C00∘C and 374∘C using synthetic FIs supplied by FLUID INCThe heatingfreezing rate is generally 02∘ to 5∘Cmin but itwas reduced to lt02∘Cmin near the phase transformationThe uncertainties for the measurements are plusmn05∘ plusmn02∘ andplusmn2∘C for runs in the range of minus120∘ to minus70∘C minus70∘ to +100∘Cand +100∘ to +600∘C respectively Ice-melting temperatureswere observed at a heating rate of less than 01∘Cmin andhomogenization temperatures at rate of le1∘Cmin

Fluid inclusions were carefully observed to identify theirgenetic and compositional types vapor-liquid ratios spatialclustering and the species The fluid inclusion petrographicstudywas based on the concept of fluid inclusion assemblages(FIAs) as described byGoldstein [24] an approach that placesfluid inclusions into assemblages that have been trappedpenecontemporaneously Fluid inclusion data was collectedfrom both primary and pseudosecondary fluid inclusionassemblages representing fluids trapped during crystalgrowth Then microthermometric data was analyzed fromtwo-three inclusions in each FIA Phase changes in every FIAgenerally occurred over 1∘ndash5∘C consistent with petrographicobservations that inclusions did not undergo postentrapmentmodification [25] Microthermometric analyses were carriedout on 258 FIAs and the results are summarized in Table 2

After careful examination of their petrography ninedoubly polished-thin sections that have adequate primaryfluid inclusions were chosen for Laser Raman spectroscopicanalysis (LRSA) LRSA was conducted at the State KeyLaboratory of Geological Processes and Mineral Resources(GPMR) China University of Geosciences Wuhan ChinaIn order to confirm the volatile species of FIs representativesamples were carried out with a Renishaw 1000 Ramanmicrospectrometer according to the method of Burke [26]Spectrograph aperture was chosen as 25120583m or 50 120583m pin-hole The spectra were recorded with counting time of 20 sto 40 s and they ranged from 50 to 3800 cmminus1

Six sphalerite samples from the main economic ore-forming stage II for conventional sulfur isotopic analyseswere collected from different localities including 1030min height 1070m in height and 1170m in height of theNanmushu zinc-lead deposit (Table 3) Conventional sulfurisotope analyses of the six samples were carried out atWuhanInstitute of Geology and Mineral Resources China Geologi-cal SurveyThese samples were first broken into 025ndash05mmfragments handpicked to gt95 purity under a binocularmicroscope and cleaned ultrasonically then crushed to lt200mesh and heated under vacuum condition with Cu2OThe SO2 gas was generated by the oxidation reaction andsulfur isotopic compositions are measured on a MAT-251 gasmass spectrometer The results are reported as 12057534S valueswith an analytical uncertainty of 02permil (2120590) Sulfur isotopiccompositions are reported in comparison with V-CDT

Geofluids 5

F

Footrill

Tunnel entrance

Fault

Zn1

Zn2

Zn1

FF

Zn3

Orebody and number

0

Ｈ1

1000(m)

Neoproterozoic Dengying Formation chert-bearing band dolomite (2dn24)

Neoproterozoic Dengying Formation breccia dolomite (2dn23)

Neoproterozoic Dengying Formation laminar dolomite (2dn22)

(a)

ZK 001

Zn1

0

340∘ 160∘

100(m)

1100

(m)

1000

Fcarbonaceous slatesLower Cambrian Guojiaba Formation

ZK 001Height

Fault

Drill hole

Geologicalboundary

Orebody and numberＨ1

1000 m

900

800

Neoproterozoic Dengying Formationchert-bearing band dolomite (2dn2

4)

Neoproterozoic Dengying Formationbreccia dolomite (2dn2

3)

Neoproterozoic Dengying Formation

laminar dolomite (2dn22)

F

(b)

Figure 3 (a) Representative simplified geologic map showing the occurrence and morphology of major orebody Zn1 at 1030m above sealevel in the Nanmushu Zn-Pb deposit (after Li et al 2007 [9]) (b) Cross-section of the Nanmushu Zn-Pb deposit (modified from Hou et al2007 [23])

4 Results

41 Paragenetic Mineralization Stages According to themin-eral assemblages and the cross-cutting relationships of theorebodies three mineralization stages are identified includ-ing the sedimentary diagenetic stage the hydrothermalore-forming stage and the post-ore supergene stage Inthe sedimentary diagenetic stage vein-type bitumen occursparallel to the country rock beddings or fractures and faraway from the orebodies (Figure 4(a)) The fine-grainedeuhedral pyrite Py(s) of this stage is 10 to 50 120583m in sizeand is disseminated within dolomite with the hydrothermal

minerals filling interspace (Figure 4(b)) The hydrothermalore-forming stage can be subdivided into three substages

Stage I Stage I characterized by the assemblage of dolomite+ quartz + pyrite + sphalerite + pyrrhotite without galena(Figure 4(c)) This type mineral assemblage usually fillsbreccias and open spaces with sphalerite impregnationIn this stage medium-grained pyrite Py(a) and medium-grained sphalerite Sp(a) vary in size ranging from 30 to100 120583m and 30 to 200120583m in diameter respectively Minorinclusions of pyrrhotite are common within the euhedralPy(a)

6 Geofluids

Table2Asummaryof

fluid

inclu

siondataforthe

Nanmushu

Zn-Pbdepo

sit

StageI

StageII

StageIII

Hostm

ineral

QSp(a)

QDol

Sp(b)

Cal

Brt

QFIssize(120583m)

3sim18

6sim11

6sim40

4sim20

4sim20

3sim14

4sim16

4sim8

Vapo

r(vol

)5sim

305sim

305sim

405sim

2010sim40

5sim25

5sim30

5sim20

Cou

ntso

fFIAs

617

3434

3043

2128

119879m(∘ C

)oftypeI

inclu

sions

minus313simminus207

minus587

minus347simminus213

ndash516

ndash513

ndash208

119879mH

H(∘ C

)oftypeI

inclu

sions

minus272simminus213

ndash370

119879ice(∘ C

)oftypeI

inclu

sions

minus94simminus24

minus76simminus38minus103simminus28minus83simminus12

minus94simminus36

minus119simminus28minus154simminus18

minus69simminus12

119879h(∘ C

)oftypeI

inclu

sions

(mean)

171sim340

225sim

314

186sim

264

152sim

265

183sim

276

107sim

202

123sim

187

149sim

195

Meanof119879h(∘ C

)239

283

223

205

238

152

165

166

Salin

ity(w

tNaC

lequ

ivalent)

43sim

133

62sim

112

47sim

143

20sim

122

59sim

133

30sim

159

31sim190

21sim104

Salin

ity(w

tNaC

l+Ca

Cl2equivalent)

66sim

116

116sim148

Bulkdensity

(gcm3)

073sim096

075sim092

085sim098

084sim098

084sim095

092sim10

3091sim10

4090sim099

Hom

ogenizationsty

leL+Vrarr

LL+Vrarr

LL+Vrarr

LLaserR

aman

spectro

scop

icanalysisof

compo

sition

H2OC

H4

H2OC

H4B

itumen

H2OC

H4C4H6B

itumen

Dom

inantaqu

eous-saltspecies

H2O-N

aCl

H2O-N

aCl-C

aCl 2plusmnMgC

l 2H2O-N

aCl-C

aCl 2plusmnMgC

l 2119879mfirstm

eltingtemperature119879

mH

Hm

eltingtemperature

ofhydroh

alite119879

icemeltingtemperature

offin

alice119879htotalh

omogenizationtemperatureB

rtbariteC

alcalciteD

oldolom

iteQ

quartzSp(a)fin

e-grainedsphaleritefrom

hydrotherm

alsta

geISp(b)coarse-grained

sphaleritefrom

hydrotherm

alstageIINo

tesSalin

ity(w

tNaC

lequ

ivalent)estim

ated

byfin

alicem

eltingtem

perature(119879

ice)oftype

Iinclusio

ns(Bod

nar1993)[13]Salin

ity(w

tNaC

l+Ca

Cl2equivalent)e

stimated

by119879m119879

mH

Hand119879iceof

type

Iinclusio

nsby

usingtheSoftw

arePackageFluids

(Steele

-MacInnise

tal2010)[16]Bu

lkdensity

oftype

Iinclu

sions

estim

ated

usingthee

quations

ofBo

dnar

(1993)[13]Dom

inantaqu

eous-saltspecies

concludedon

theb

asisof119879mandthem

icrothermom

etry

behavior

offlu

idinclu

sions

Geofluids 7

Table 3 Sulfur isotopic data of sulfides and sulfate from the Mayuan district

Sample ID Location Mineral 12057534S (permil) Data sourceNMS-1170-14 Nanmushu Sphalerite +183 This studyNMS-1030-2 Nanmushu Sphalerite +174 This studyNMS-1170-13 Nanmushu Sphalerite +180 This studyNMS-1070-13 Nanmushu Sphalerite +176 This studyNMS-1030-3 Nanmushu Sphalerite +174 This studyNMS-1070-2 Nanmushu Sphalerite +178 This studyMAYN-1 Nanmushu Sphalerite +189 Li et al 2007 [9]MAYN-2 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-3 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-4 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-5 Nanmushu Sphalerite +181 Li et al 2007 [9]MAYN-6 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-7 Nanmushu Sphalerite +194 Li et al 2007 [9]MY-8 Nanmushu Sphalerite +170 Wang et al 2008 [7]S-1 Nanmushu Sphalerite +178 Wang et al 2008 [7]S-2 Nanmushu Sphalerite +180 Wang et al 2008 [7]MWT1 Nanmushu Sphalerite +182 Hou et al 2007 [17]MWT3 Nanmushu Sphalerite +179 Hou et al 2007 [17]H-1 Nanmushu Pyrite +188 Wang et al 2008 [7]H-2 Nanmushu Pyrite +186 Wang et al 2008 [7]F-1 Nanmushu Galena +168 Wang et al 2008 [7]F-2 Nanmushu Galena +166 Wang et al 2008 [7]F-3 Nanmushu Galena +156 Wang et al 2008 [7]MWT2 Nanmushu Barite +322 Hou et al 2007 [17]MWT5-1 Zhujiahe Barite +333 Hou et al 2007 [17]MWT5-2 Zhujiahe Barite +335 Hou et al 2007 [17]KXG-9 Kongxigou Sphalerite +160 Wang et al 2008 [7]MWT4 Nanrsquoanshan Galena +129 Hou et al 2007 [17]Note Nanmushu and Kongxigou deposits are from South ore zone of Mayuan district and Zhujiahe and Nanrsquoanshan are ore deposits (spots) fromMiddle orezone of Mayuan district

Stage II Stage II is dominated by the widespread coarse-grained sphalerite Sp(b) and galena as well as minor amountof coarse-grained pyrite Py(b) Zn-Pbmineralization starts atstage I and continues with sphalerite impregnation followedby galena + sphalerite impregnation which subordinate stageII The cross-cutting relationships of stage I and stage II areobserved and shown in Figure 4(d) Stage II is themajormin-eralization stage for zinc and leadThismineralization stage ismost important in terms of tonnage andmining Major typesof ores include breccia-type vein-type (Figure 4(d)) andhigh-grade massive sulfide type (Figure 4(e)) with a simplemineralogy dominated by sphalerite galena and pyrite inthis stage Bitumen Bit(a) can also be observed in this stage(Figure 4(f)) occurring in vein-type and breccia-type oresand usually associating with contemporary sphalerite andgalena and gangue minerals such as dolomite calcite andquartz The Py(b) in this stage surrounded the Sp(b) orfilled the fractures of Sp(b) and galena grains (Figure 4(g))indicating a relatively late timing of formation

Stage III Stage III marked the end of hydrothermal ore-forming epoch and was characterized by quartz + barite +

calcite + bitumen Abundant bitumens Bit(b) in this stageare emulsion drops filling the open interspace between othergangue minerals and concentrated along crystal interface ofgangue minerals as well as microfissuring or pores (Figures4(h) and 4(i)) implying the bitumen might have formed alittle later than the gangue minerals

In the supergene stage oxide minerals include smith-sonite cerusite and limonite A paragenetic sequence forminerals in the Nanmushu Zn-Pb deposit is summarized inFigure 5

42 Fluid Inclusions Petrography and Laser Raman Spec-troscopic Analysis Samples of sphalerite (Sp(a) and Sp(b))dolomite quartz calcite and barite were selected from threehydrothermal stages in the Nanmushu deposit to determinethe nature of the fluids associated with mineralizationAbundant primary pseudosecondary and secondary FIsin these minerals are found In order to avoid erroneousinterpretations secondary FIs andor FIs which partiallydecrepitate during the microthermometric processes werenot documented during experiment FIs were studied insamples that are characterized with absence of plentiful

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

4 Geofluids

Table 1 Main characteristics of orebodies in the Nanmushu Zn-Pb deposit

Number Length (m) Thickness (m) Zn grade (wt) Pb grade (wt)Range Average Range Average Range Average

Zn1 2560 15sim325 76 15sim114 45Zn2 180 10sim53 28 13sim34 25Zn3 260 05sim64 21 27sim131 41Zn4 106 13 13 14 14Zn5 100 17sim25 21 17sim19 18PbZn1 86 16 16 19 19 24 24PbZn2 160 08sim84 46 11sim32 30 09 09PbZn3 160 58 58 11sim64 53 33 33

controlled by the third bed of the Dengying Formation(Z21198891198992

3) It can be considered that the cavity filling wasformed mainly by hydrothermal mineralization Hou et al[19 20] described the Zn1 as amajor ore shoot which extends2560m and broadens 15ndash325m (average thickness at 76m)with zinc grade at 15ndash114 wt (average value at 45 wt)(Table 1) with the ore shoot occupying a dilational flexurein the 1030m height (Figure 3) Hydrothermal alterationin the Nanmushu Zn-Pb deposit comprising silicificationand carbonate alteration is not extensive and it is notclosely related to mineralization The shapes of orebodies arestratiform-like lenticular and vein and majority of themare strata-bounded and controlled by the bedding-parallelfractures

3 Samples and Analytical Methods

Samples were collected from the Nanmushu Zn-Pb depositin the open pit at elevations of 1030m 1070m and 1170mrespectively Polished blocks and thin sections were initiallyexamined by reflected and transmitted light microscopy tocharacterize the mineralogy textures and parageneses

Twenty-nine doubly polished-thin sections (100120583mthick) of quartz dolomite barite calcite and sphalerite wereprepared from representative samples of the three hydro-thermal mineralization stages (I II and III) Petrographicexamination of fluid inclusions was conducted using a NikonE80I microscope with an ultraviolet (UV) attachment usingmedium-width bandpass excitation filters (330ndash380 nm)Oil-bearing fluid inclusions were identified by their fluores-cence under UV excitation Microthermometric measure-ments were conducted using a LinkhamTHMS-600Heating-Freezing Systems (from minus196∘ to 550∘C) equipped with aNikon E80I microscope at China University of GeosciencesWuhan China Thermocouples were calibrated at minus566∘C00∘C and 374∘C using synthetic FIs supplied by FLUID INCThe heatingfreezing rate is generally 02∘ to 5∘Cmin but itwas reduced to lt02∘Cmin near the phase transformationThe uncertainties for the measurements are plusmn05∘ plusmn02∘ andplusmn2∘C for runs in the range of minus120∘ to minus70∘C minus70∘ to +100∘Cand +100∘ to +600∘C respectively Ice-melting temperatureswere observed at a heating rate of less than 01∘Cmin andhomogenization temperatures at rate of le1∘Cmin

Fluid inclusions were carefully observed to identify theirgenetic and compositional types vapor-liquid ratios spatialclustering and the species The fluid inclusion petrographicstudywas based on the concept of fluid inclusion assemblages(FIAs) as described byGoldstein [24] an approach that placesfluid inclusions into assemblages that have been trappedpenecontemporaneously Fluid inclusion data was collectedfrom both primary and pseudosecondary fluid inclusionassemblages representing fluids trapped during crystalgrowth Then microthermometric data was analyzed fromtwo-three inclusions in each FIA Phase changes in every FIAgenerally occurred over 1∘ndash5∘C consistent with petrographicobservations that inclusions did not undergo postentrapmentmodification [25] Microthermometric analyses were carriedout on 258 FIAs and the results are summarized in Table 2

After careful examination of their petrography ninedoubly polished-thin sections that have adequate primaryfluid inclusions were chosen for Laser Raman spectroscopicanalysis (LRSA) LRSA was conducted at the State KeyLaboratory of Geological Processes and Mineral Resources(GPMR) China University of Geosciences Wuhan ChinaIn order to confirm the volatile species of FIs representativesamples were carried out with a Renishaw 1000 Ramanmicrospectrometer according to the method of Burke [26]Spectrograph aperture was chosen as 25120583m or 50 120583m pin-hole The spectra were recorded with counting time of 20 sto 40 s and they ranged from 50 to 3800 cmminus1

Six sphalerite samples from the main economic ore-forming stage II for conventional sulfur isotopic analyseswere collected from different localities including 1030min height 1070m in height and 1170m in height of theNanmushu zinc-lead deposit (Table 3) Conventional sulfurisotope analyses of the six samples were carried out atWuhanInstitute of Geology and Mineral Resources China Geologi-cal SurveyThese samples were first broken into 025ndash05mmfragments handpicked to gt95 purity under a binocularmicroscope and cleaned ultrasonically then crushed to lt200mesh and heated under vacuum condition with Cu2OThe SO2 gas was generated by the oxidation reaction andsulfur isotopic compositions are measured on a MAT-251 gasmass spectrometer The results are reported as 12057534S valueswith an analytical uncertainty of 02permil (2120590) Sulfur isotopiccompositions are reported in comparison with V-CDT

Geofluids 5

F

Footrill

Tunnel entrance

Fault

Zn1

Zn2

Zn1

FF

Zn3

Orebody and number

0

Ｈ1

1000(m)

Neoproterozoic Dengying Formation chert-bearing band dolomite (2dn24)

Neoproterozoic Dengying Formation breccia dolomite (2dn23)

Neoproterozoic Dengying Formation laminar dolomite (2dn22)

(a)

ZK 001

Zn1

0

340∘ 160∘

100(m)

1100

(m)

1000

Fcarbonaceous slatesLower Cambrian Guojiaba Formation

ZK 001Height

Fault

Drill hole

Geologicalboundary

Orebody and numberＨ1

1000 m

900

800

Neoproterozoic Dengying Formationchert-bearing band dolomite (2dn2

4)

Neoproterozoic Dengying Formationbreccia dolomite (2dn2

3)

Neoproterozoic Dengying Formation

laminar dolomite (2dn22)

F

(b)

Figure 3 (a) Representative simplified geologic map showing the occurrence and morphology of major orebody Zn1 at 1030m above sealevel in the Nanmushu Zn-Pb deposit (after Li et al 2007 [9]) (b) Cross-section of the Nanmushu Zn-Pb deposit (modified from Hou et al2007 [23])

4 Results

41 Paragenetic Mineralization Stages According to themin-eral assemblages and the cross-cutting relationships of theorebodies three mineralization stages are identified includ-ing the sedimentary diagenetic stage the hydrothermalore-forming stage and the post-ore supergene stage Inthe sedimentary diagenetic stage vein-type bitumen occursparallel to the country rock beddings or fractures and faraway from the orebodies (Figure 4(a)) The fine-grainedeuhedral pyrite Py(s) of this stage is 10 to 50 120583m in sizeand is disseminated within dolomite with the hydrothermal

minerals filling interspace (Figure 4(b)) The hydrothermalore-forming stage can be subdivided into three substages

Stage I Stage I characterized by the assemblage of dolomite+ quartz + pyrite + sphalerite + pyrrhotite without galena(Figure 4(c)) This type mineral assemblage usually fillsbreccias and open spaces with sphalerite impregnationIn this stage medium-grained pyrite Py(a) and medium-grained sphalerite Sp(a) vary in size ranging from 30 to100 120583m and 30 to 200120583m in diameter respectively Minorinclusions of pyrrhotite are common within the euhedralPy(a)

6 Geofluids

Table2Asummaryof

fluid

inclu

siondataforthe

Nanmushu

Zn-Pbdepo

sit

StageI

StageII

StageIII

Hostm

ineral

QSp(a)

QDol

Sp(b)

Cal

Brt

QFIssize(120583m)

3sim18

6sim11

6sim40

4sim20

4sim20

3sim14

4sim16

4sim8

Vapo

r(vol

)5sim

305sim

305sim

405sim

2010sim40

5sim25

5sim30

5sim20

Cou

ntso

fFIAs

617

3434

3043

2128

119879m(∘ C

)oftypeI

inclu

sions

minus313simminus207

minus587

minus347simminus213

ndash516

ndash513

ndash208

119879mH

H(∘ C

)oftypeI

inclu

sions

minus272simminus213

ndash370

119879ice(∘ C

)oftypeI

inclu

sions

minus94simminus24

minus76simminus38minus103simminus28minus83simminus12

minus94simminus36

minus119simminus28minus154simminus18

minus69simminus12

119879h(∘ C

)oftypeI

inclu

sions

(mean)

171sim340

225sim

314

186sim

264

152sim

265

183sim

276

107sim

202

123sim

187

149sim

195

Meanof119879h(∘ C

)239

283

223

205

238

152

165

166

Salin

ity(w

tNaC

lequ

ivalent)

43sim

133

62sim

112

47sim

143

20sim

122

59sim

133

30sim

159

31sim190

21sim104

Salin

ity(w

tNaC

l+Ca

Cl2equivalent)

66sim

116

116sim148

Bulkdensity

(gcm3)

073sim096

075sim092

085sim098

084sim098

084sim095

092sim10

3091sim10

4090sim099

Hom

ogenizationsty

leL+Vrarr

LL+Vrarr

LL+Vrarr

LLaserR

aman

spectro

scop

icanalysisof

compo

sition

H2OC

H4

H2OC

H4B

itumen

H2OC

H4C4H6B

itumen

Dom

inantaqu

eous-saltspecies

H2O-N

aCl

H2O-N

aCl-C

aCl 2plusmnMgC

l 2H2O-N

aCl-C

aCl 2plusmnMgC

l 2119879mfirstm

eltingtemperature119879

mH

Hm

eltingtemperature

ofhydroh

alite119879

icemeltingtemperature

offin

alice119879htotalh

omogenizationtemperatureB

rtbariteC

alcalciteD

oldolom

iteQ

quartzSp(a)fin

e-grainedsphaleritefrom

hydrotherm

alsta

geISp(b)coarse-grained

sphaleritefrom

hydrotherm

alstageIINo

tesSalin

ity(w

tNaC

lequ

ivalent)estim

ated

byfin

alicem

eltingtem

perature(119879

ice)oftype

Iinclusio

ns(Bod

nar1993)[13]Salin

ity(w

tNaC

l+Ca

Cl2equivalent)e

stimated

by119879m119879

mH

Hand119879iceof

type

Iinclusio

nsby

usingtheSoftw

arePackageFluids

(Steele

-MacInnise

tal2010)[16]Bu

lkdensity

oftype

Iinclu

sions

estim

ated

usingthee

quations

ofBo

dnar

(1993)[13]Dom

inantaqu

eous-saltspecies

concludedon

theb

asisof119879mandthem

icrothermom

etry

behavior

offlu

idinclu

sions

Geofluids 7

Table 3 Sulfur isotopic data of sulfides and sulfate from the Mayuan district

Sample ID Location Mineral 12057534S (permil) Data sourceNMS-1170-14 Nanmushu Sphalerite +183 This studyNMS-1030-2 Nanmushu Sphalerite +174 This studyNMS-1170-13 Nanmushu Sphalerite +180 This studyNMS-1070-13 Nanmushu Sphalerite +176 This studyNMS-1030-3 Nanmushu Sphalerite +174 This studyNMS-1070-2 Nanmushu Sphalerite +178 This studyMAYN-1 Nanmushu Sphalerite +189 Li et al 2007 [9]MAYN-2 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-3 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-4 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-5 Nanmushu Sphalerite +181 Li et al 2007 [9]MAYN-6 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-7 Nanmushu Sphalerite +194 Li et al 2007 [9]MY-8 Nanmushu Sphalerite +170 Wang et al 2008 [7]S-1 Nanmushu Sphalerite +178 Wang et al 2008 [7]S-2 Nanmushu Sphalerite +180 Wang et al 2008 [7]MWT1 Nanmushu Sphalerite +182 Hou et al 2007 [17]MWT3 Nanmushu Sphalerite +179 Hou et al 2007 [17]H-1 Nanmushu Pyrite +188 Wang et al 2008 [7]H-2 Nanmushu Pyrite +186 Wang et al 2008 [7]F-1 Nanmushu Galena +168 Wang et al 2008 [7]F-2 Nanmushu Galena +166 Wang et al 2008 [7]F-3 Nanmushu Galena +156 Wang et al 2008 [7]MWT2 Nanmushu Barite +322 Hou et al 2007 [17]MWT5-1 Zhujiahe Barite +333 Hou et al 2007 [17]MWT5-2 Zhujiahe Barite +335 Hou et al 2007 [17]KXG-9 Kongxigou Sphalerite +160 Wang et al 2008 [7]MWT4 Nanrsquoanshan Galena +129 Hou et al 2007 [17]Note Nanmushu and Kongxigou deposits are from South ore zone of Mayuan district and Zhujiahe and Nanrsquoanshan are ore deposits (spots) fromMiddle orezone of Mayuan district

Stage II Stage II is dominated by the widespread coarse-grained sphalerite Sp(b) and galena as well as minor amountof coarse-grained pyrite Py(b) Zn-Pbmineralization starts atstage I and continues with sphalerite impregnation followedby galena + sphalerite impregnation which subordinate stageII The cross-cutting relationships of stage I and stage II areobserved and shown in Figure 4(d) Stage II is themajormin-eralization stage for zinc and leadThismineralization stage ismost important in terms of tonnage andmining Major typesof ores include breccia-type vein-type (Figure 4(d)) andhigh-grade massive sulfide type (Figure 4(e)) with a simplemineralogy dominated by sphalerite galena and pyrite inthis stage Bitumen Bit(a) can also be observed in this stage(Figure 4(f)) occurring in vein-type and breccia-type oresand usually associating with contemporary sphalerite andgalena and gangue minerals such as dolomite calcite andquartz The Py(b) in this stage surrounded the Sp(b) orfilled the fractures of Sp(b) and galena grains (Figure 4(g))indicating a relatively late timing of formation

Stage III Stage III marked the end of hydrothermal ore-forming epoch and was characterized by quartz + barite +

calcite + bitumen Abundant bitumens Bit(b) in this stageare emulsion drops filling the open interspace between othergangue minerals and concentrated along crystal interface ofgangue minerals as well as microfissuring or pores (Figures4(h) and 4(i)) implying the bitumen might have formed alittle later than the gangue minerals

In the supergene stage oxide minerals include smith-sonite cerusite and limonite A paragenetic sequence forminerals in the Nanmushu Zn-Pb deposit is summarized inFigure 5

42 Fluid Inclusions Petrography and Laser Raman Spec-troscopic Analysis Samples of sphalerite (Sp(a) and Sp(b))dolomite quartz calcite and barite were selected from threehydrothermal stages in the Nanmushu deposit to determinethe nature of the fluids associated with mineralizationAbundant primary pseudosecondary and secondary FIsin these minerals are found In order to avoid erroneousinterpretations secondary FIs andor FIs which partiallydecrepitate during the microthermometric processes werenot documented during experiment FIs were studied insamples that are characterized with absence of plentiful

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 5

F

Footrill

Tunnel entrance

Fault

Zn1

Zn2

Zn1

FF

Zn3

Orebody and number

0

Ｈ1

1000(m)

Neoproterozoic Dengying Formation chert-bearing band dolomite (2dn24)

Neoproterozoic Dengying Formation breccia dolomite (2dn23)

Neoproterozoic Dengying Formation laminar dolomite (2dn22)

(a)

ZK 001

Zn1

0

340∘ 160∘

100(m)

1100

(m)

1000

Fcarbonaceous slatesLower Cambrian Guojiaba Formation

ZK 001Height

Fault

Drill hole

Geologicalboundary

Orebody and numberＨ1

1000 m

900

800

Neoproterozoic Dengying Formationchert-bearing band dolomite (2dn2

4)

Neoproterozoic Dengying Formationbreccia dolomite (2dn2

3)

Neoproterozoic Dengying Formation

laminar dolomite (2dn22)

F

(b)

Figure 3 (a) Representative simplified geologic map showing the occurrence and morphology of major orebody Zn1 at 1030m above sealevel in the Nanmushu Zn-Pb deposit (after Li et al 2007 [9]) (b) Cross-section of the Nanmushu Zn-Pb deposit (modified from Hou et al2007 [23])

4 Results

41 Paragenetic Mineralization Stages According to themin-eral assemblages and the cross-cutting relationships of theorebodies three mineralization stages are identified includ-ing the sedimentary diagenetic stage the hydrothermalore-forming stage and the post-ore supergene stage Inthe sedimentary diagenetic stage vein-type bitumen occursparallel to the country rock beddings or fractures and faraway from the orebodies (Figure 4(a)) The fine-grainedeuhedral pyrite Py(s) of this stage is 10 to 50 120583m in sizeand is disseminated within dolomite with the hydrothermal

minerals filling interspace (Figure 4(b)) The hydrothermalore-forming stage can be subdivided into three substages

Stage I Stage I characterized by the assemblage of dolomite+ quartz + pyrite + sphalerite + pyrrhotite without galena(Figure 4(c)) This type mineral assemblage usually fillsbreccias and open spaces with sphalerite impregnationIn this stage medium-grained pyrite Py(a) and medium-grained sphalerite Sp(a) vary in size ranging from 30 to100 120583m and 30 to 200120583m in diameter respectively Minorinclusions of pyrrhotite are common within the euhedralPy(a)

6 Geofluids

Table2Asummaryof

fluid

inclu

siondataforthe

Nanmushu

Zn-Pbdepo

sit

StageI

StageII

StageIII

Hostm

ineral

QSp(a)

QDol

Sp(b)

Cal

Brt

QFIssize(120583m)

3sim18

6sim11

6sim40

4sim20

4sim20

3sim14

4sim16

4sim8

Vapo

r(vol

)5sim

305sim

305sim

405sim

2010sim40

5sim25

5sim30

5sim20

Cou

ntso

fFIAs

617

3434

3043

2128

119879m(∘ C

)oftypeI

inclu

sions

minus313simminus207

minus587

minus347simminus213

ndash516

ndash513

ndash208

119879mH

H(∘ C

)oftypeI

inclu

sions

minus272simminus213

ndash370

119879ice(∘ C

)oftypeI

inclu

sions

minus94simminus24

minus76simminus38minus103simminus28minus83simminus12

minus94simminus36

minus119simminus28minus154simminus18

minus69simminus12

119879h(∘ C

)oftypeI

inclu

sions

(mean)

171sim340

225sim

314

186sim

264

152sim

265

183sim

276

107sim

202

123sim

187

149sim

195

Meanof119879h(∘ C

)239

283

223

205

238

152

165

166

Salin

ity(w

tNaC

lequ

ivalent)

43sim

133

62sim

112

47sim

143

20sim

122

59sim

133

30sim

159

31sim190

21sim104

Salin

ity(w

tNaC

l+Ca

Cl2equivalent)

66sim

116

116sim148

Bulkdensity

(gcm3)

073sim096

075sim092

085sim098

084sim098

084sim095

092sim10

3091sim10

4090sim099

Hom

ogenizationsty

leL+Vrarr

LL+Vrarr

LL+Vrarr

LLaserR

aman

spectro

scop

icanalysisof

compo

sition

H2OC

H4

H2OC

H4B

itumen

H2OC

H4C4H6B

itumen

Dom

inantaqu

eous-saltspecies

H2O-N

aCl

H2O-N

aCl-C

aCl 2plusmnMgC

l 2H2O-N

aCl-C

aCl 2plusmnMgC

l 2119879mfirstm

eltingtemperature119879

mH

Hm

eltingtemperature

ofhydroh

alite119879

icemeltingtemperature

offin

alice119879htotalh

omogenizationtemperatureB

rtbariteC

alcalciteD

oldolom

iteQ

quartzSp(a)fin

e-grainedsphaleritefrom

hydrotherm

alsta

geISp(b)coarse-grained

sphaleritefrom

hydrotherm

alstageIINo

tesSalin

ity(w

tNaC

lequ

ivalent)estim

ated

byfin

alicem

eltingtem

perature(119879

ice)oftype

Iinclusio

ns(Bod

nar1993)[13]Salin

ity(w

tNaC

l+Ca

Cl2equivalent)e

stimated

by119879m119879

mH

Hand119879iceof

type

Iinclusio

nsby

usingtheSoftw

arePackageFluids

(Steele

-MacInnise

tal2010)[16]Bu

lkdensity

oftype

Iinclu

sions

estim

ated

usingthee

quations

ofBo

dnar

(1993)[13]Dom

inantaqu

eous-saltspecies

concludedon

theb

asisof119879mandthem

icrothermom

etry

behavior

offlu

idinclu

sions

Geofluids 7

Table 3 Sulfur isotopic data of sulfides and sulfate from the Mayuan district

Sample ID Location Mineral 12057534S (permil) Data sourceNMS-1170-14 Nanmushu Sphalerite +183 This studyNMS-1030-2 Nanmushu Sphalerite +174 This studyNMS-1170-13 Nanmushu Sphalerite +180 This studyNMS-1070-13 Nanmushu Sphalerite +176 This studyNMS-1030-3 Nanmushu Sphalerite +174 This studyNMS-1070-2 Nanmushu Sphalerite +178 This studyMAYN-1 Nanmushu Sphalerite +189 Li et al 2007 [9]MAYN-2 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-3 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-4 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-5 Nanmushu Sphalerite +181 Li et al 2007 [9]MAYN-6 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-7 Nanmushu Sphalerite +194 Li et al 2007 [9]MY-8 Nanmushu Sphalerite +170 Wang et al 2008 [7]S-1 Nanmushu Sphalerite +178 Wang et al 2008 [7]S-2 Nanmushu Sphalerite +180 Wang et al 2008 [7]MWT1 Nanmushu Sphalerite +182 Hou et al 2007 [17]MWT3 Nanmushu Sphalerite +179 Hou et al 2007 [17]H-1 Nanmushu Pyrite +188 Wang et al 2008 [7]H-2 Nanmushu Pyrite +186 Wang et al 2008 [7]F-1 Nanmushu Galena +168 Wang et al 2008 [7]F-2 Nanmushu Galena +166 Wang et al 2008 [7]F-3 Nanmushu Galena +156 Wang et al 2008 [7]MWT2 Nanmushu Barite +322 Hou et al 2007 [17]MWT5-1 Zhujiahe Barite +333 Hou et al 2007 [17]MWT5-2 Zhujiahe Barite +335 Hou et al 2007 [17]KXG-9 Kongxigou Sphalerite +160 Wang et al 2008 [7]MWT4 Nanrsquoanshan Galena +129 Hou et al 2007 [17]Note Nanmushu and Kongxigou deposits are from South ore zone of Mayuan district and Zhujiahe and Nanrsquoanshan are ore deposits (spots) fromMiddle orezone of Mayuan district

Stage II Stage II is dominated by the widespread coarse-grained sphalerite Sp(b) and galena as well as minor amountof coarse-grained pyrite Py(b) Zn-Pbmineralization starts atstage I and continues with sphalerite impregnation followedby galena + sphalerite impregnation which subordinate stageII The cross-cutting relationships of stage I and stage II areobserved and shown in Figure 4(d) Stage II is themajormin-eralization stage for zinc and leadThismineralization stage ismost important in terms of tonnage andmining Major typesof ores include breccia-type vein-type (Figure 4(d)) andhigh-grade massive sulfide type (Figure 4(e)) with a simplemineralogy dominated by sphalerite galena and pyrite inthis stage Bitumen Bit(a) can also be observed in this stage(Figure 4(f)) occurring in vein-type and breccia-type oresand usually associating with contemporary sphalerite andgalena and gangue minerals such as dolomite calcite andquartz The Py(b) in this stage surrounded the Sp(b) orfilled the fractures of Sp(b) and galena grains (Figure 4(g))indicating a relatively late timing of formation

Stage III Stage III marked the end of hydrothermal ore-forming epoch and was characterized by quartz + barite +

calcite + bitumen Abundant bitumens Bit(b) in this stageare emulsion drops filling the open interspace between othergangue minerals and concentrated along crystal interface ofgangue minerals as well as microfissuring or pores (Figures4(h) and 4(i)) implying the bitumen might have formed alittle later than the gangue minerals

In the supergene stage oxide minerals include smith-sonite cerusite and limonite A paragenetic sequence forminerals in the Nanmushu Zn-Pb deposit is summarized inFigure 5

42 Fluid Inclusions Petrography and Laser Raman Spec-troscopic Analysis Samples of sphalerite (Sp(a) and Sp(b))dolomite quartz calcite and barite were selected from threehydrothermal stages in the Nanmushu deposit to determinethe nature of the fluids associated with mineralizationAbundant primary pseudosecondary and secondary FIsin these minerals are found In order to avoid erroneousinterpretations secondary FIs andor FIs which partiallydecrepitate during the microthermometric processes werenot documented during experiment FIs were studied insamples that are characterized with absence of plentiful

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

6 Geofluids

Table2Asummaryof

fluid

inclu

siondataforthe

Nanmushu

Zn-Pbdepo

sit

StageI

StageII

StageIII

Hostm

ineral

QSp(a)

QDol

Sp(b)

Cal

Brt

QFIssize(120583m)

3sim18

6sim11

6sim40

4sim20

4sim20

3sim14

4sim16

4sim8

Vapo

r(vol

)5sim

305sim

305sim

405sim

2010sim40

5sim25

5sim30

5sim20

Cou

ntso

fFIAs

617

3434

3043

2128

119879m(∘ C

)oftypeI

inclu

sions

minus313simminus207

minus587

minus347simminus213

ndash516

ndash513

ndash208

119879mH

H(∘ C

)oftypeI

inclu

sions

minus272simminus213

ndash370

119879ice(∘ C

)oftypeI

inclu

sions

minus94simminus24

minus76simminus38minus103simminus28minus83simminus12

minus94simminus36

minus119simminus28minus154simminus18

minus69simminus12

119879h(∘ C

)oftypeI

inclu

sions

(mean)

171sim340

225sim

314

186sim

264

152sim

265

183sim

276

107sim

202

123sim

187

149sim

195

Meanof119879h(∘ C

)239

283

223

205

238

152

165

166

Salin

ity(w

tNaC

lequ

ivalent)

43sim

133

62sim

112

47sim

143

20sim

122

59sim

133

30sim

159

31sim190

21sim104

Salin

ity(w

tNaC

l+Ca

Cl2equivalent)

66sim

116

116sim148

Bulkdensity

(gcm3)

073sim096

075sim092

085sim098

084sim098

084sim095

092sim10

3091sim10

4090sim099

Hom

ogenizationsty

leL+Vrarr

LL+Vrarr

LL+Vrarr

LLaserR

aman

spectro

scop

icanalysisof

compo

sition

H2OC

H4

H2OC

H4B

itumen

H2OC

H4C4H6B

itumen

Dom

inantaqu

eous-saltspecies

H2O-N

aCl

H2O-N

aCl-C

aCl 2plusmnMgC

l 2H2O-N

aCl-C

aCl 2plusmnMgC

l 2119879mfirstm

eltingtemperature119879

mH

Hm

eltingtemperature

ofhydroh

alite119879

icemeltingtemperature

offin

alice119879htotalh

omogenizationtemperatureB

rtbariteC

alcalciteD

oldolom

iteQ

quartzSp(a)fin

e-grainedsphaleritefrom

hydrotherm

alsta

geISp(b)coarse-grained

sphaleritefrom

hydrotherm

alstageIINo

tesSalin

ity(w

tNaC

lequ

ivalent)estim

ated

byfin

alicem

eltingtem

perature(119879

ice)oftype

Iinclusio

ns(Bod

nar1993)[13]Salin

ity(w

tNaC

l+Ca

Cl2equivalent)e

stimated

by119879m119879

mH

Hand119879iceof

type

Iinclusio

nsby

usingtheSoftw

arePackageFluids

(Steele

-MacInnise

tal2010)[16]Bu

lkdensity

oftype

Iinclu

sions

estim

ated

usingthee

quations

ofBo

dnar

(1993)[13]Dom

inantaqu

eous-saltspecies

concludedon

theb

asisof119879mandthem

icrothermom

etry

behavior

offlu

idinclu

sions

Geofluids 7

Table 3 Sulfur isotopic data of sulfides and sulfate from the Mayuan district

Sample ID Location Mineral 12057534S (permil) Data sourceNMS-1170-14 Nanmushu Sphalerite +183 This studyNMS-1030-2 Nanmushu Sphalerite +174 This studyNMS-1170-13 Nanmushu Sphalerite +180 This studyNMS-1070-13 Nanmushu Sphalerite +176 This studyNMS-1030-3 Nanmushu Sphalerite +174 This studyNMS-1070-2 Nanmushu Sphalerite +178 This studyMAYN-1 Nanmushu Sphalerite +189 Li et al 2007 [9]MAYN-2 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-3 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-4 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-5 Nanmushu Sphalerite +181 Li et al 2007 [9]MAYN-6 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-7 Nanmushu Sphalerite +194 Li et al 2007 [9]MY-8 Nanmushu Sphalerite +170 Wang et al 2008 [7]S-1 Nanmushu Sphalerite +178 Wang et al 2008 [7]S-2 Nanmushu Sphalerite +180 Wang et al 2008 [7]MWT1 Nanmushu Sphalerite +182 Hou et al 2007 [17]MWT3 Nanmushu Sphalerite +179 Hou et al 2007 [17]H-1 Nanmushu Pyrite +188 Wang et al 2008 [7]H-2 Nanmushu Pyrite +186 Wang et al 2008 [7]F-1 Nanmushu Galena +168 Wang et al 2008 [7]F-2 Nanmushu Galena +166 Wang et al 2008 [7]F-3 Nanmushu Galena +156 Wang et al 2008 [7]MWT2 Nanmushu Barite +322 Hou et al 2007 [17]MWT5-1 Zhujiahe Barite +333 Hou et al 2007 [17]MWT5-2 Zhujiahe Barite +335 Hou et al 2007 [17]KXG-9 Kongxigou Sphalerite +160 Wang et al 2008 [7]MWT4 Nanrsquoanshan Galena +129 Hou et al 2007 [17]Note Nanmushu and Kongxigou deposits are from South ore zone of Mayuan district and Zhujiahe and Nanrsquoanshan are ore deposits (spots) fromMiddle orezone of Mayuan district

Stage II Stage II is dominated by the widespread coarse-grained sphalerite Sp(b) and galena as well as minor amountof coarse-grained pyrite Py(b) Zn-Pbmineralization starts atstage I and continues with sphalerite impregnation followedby galena + sphalerite impregnation which subordinate stageII The cross-cutting relationships of stage I and stage II areobserved and shown in Figure 4(d) Stage II is themajormin-eralization stage for zinc and leadThismineralization stage ismost important in terms of tonnage andmining Major typesof ores include breccia-type vein-type (Figure 4(d)) andhigh-grade massive sulfide type (Figure 4(e)) with a simplemineralogy dominated by sphalerite galena and pyrite inthis stage Bitumen Bit(a) can also be observed in this stage(Figure 4(f)) occurring in vein-type and breccia-type oresand usually associating with contemporary sphalerite andgalena and gangue minerals such as dolomite calcite andquartz The Py(b) in this stage surrounded the Sp(b) orfilled the fractures of Sp(b) and galena grains (Figure 4(g))indicating a relatively late timing of formation

Stage III Stage III marked the end of hydrothermal ore-forming epoch and was characterized by quartz + barite +

calcite + bitumen Abundant bitumens Bit(b) in this stageare emulsion drops filling the open interspace between othergangue minerals and concentrated along crystal interface ofgangue minerals as well as microfissuring or pores (Figures4(h) and 4(i)) implying the bitumen might have formed alittle later than the gangue minerals

In the supergene stage oxide minerals include smith-sonite cerusite and limonite A paragenetic sequence forminerals in the Nanmushu Zn-Pb deposit is summarized inFigure 5

42 Fluid Inclusions Petrography and Laser Raman Spec-troscopic Analysis Samples of sphalerite (Sp(a) and Sp(b))dolomite quartz calcite and barite were selected from threehydrothermal stages in the Nanmushu deposit to determinethe nature of the fluids associated with mineralizationAbundant primary pseudosecondary and secondary FIsin these minerals are found In order to avoid erroneousinterpretations secondary FIs andor FIs which partiallydecrepitate during the microthermometric processes werenot documented during experiment FIs were studied insamples that are characterized with absence of plentiful

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EarthquakesJournal of

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Mining

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International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 7

Table 3 Sulfur isotopic data of sulfides and sulfate from the Mayuan district

Sample ID Location Mineral 12057534S (permil) Data sourceNMS-1170-14 Nanmushu Sphalerite +183 This studyNMS-1030-2 Nanmushu Sphalerite +174 This studyNMS-1170-13 Nanmushu Sphalerite +180 This studyNMS-1070-13 Nanmushu Sphalerite +176 This studyNMS-1030-3 Nanmushu Sphalerite +174 This studyNMS-1070-2 Nanmushu Sphalerite +178 This studyMAYN-1 Nanmushu Sphalerite +189 Li et al 2007 [9]MAYN-2 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-3 Nanmushu Sphalerite +177 Li et al 2007 [9]MAYN-4 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-5 Nanmushu Sphalerite +181 Li et al 2007 [9]MAYN-6 Nanmushu Sphalerite +185 Li et al 2007 [9]MAYN-7 Nanmushu Sphalerite +194 Li et al 2007 [9]MY-8 Nanmushu Sphalerite +170 Wang et al 2008 [7]S-1 Nanmushu Sphalerite +178 Wang et al 2008 [7]S-2 Nanmushu Sphalerite +180 Wang et al 2008 [7]MWT1 Nanmushu Sphalerite +182 Hou et al 2007 [17]MWT3 Nanmushu Sphalerite +179 Hou et al 2007 [17]H-1 Nanmushu Pyrite +188 Wang et al 2008 [7]H-2 Nanmushu Pyrite +186 Wang et al 2008 [7]F-1 Nanmushu Galena +168 Wang et al 2008 [7]F-2 Nanmushu Galena +166 Wang et al 2008 [7]F-3 Nanmushu Galena +156 Wang et al 2008 [7]MWT2 Nanmushu Barite +322 Hou et al 2007 [17]MWT5-1 Zhujiahe Barite +333 Hou et al 2007 [17]MWT5-2 Zhujiahe Barite +335 Hou et al 2007 [17]KXG-9 Kongxigou Sphalerite +160 Wang et al 2008 [7]MWT4 Nanrsquoanshan Galena +129 Hou et al 2007 [17]Note Nanmushu and Kongxigou deposits are from South ore zone of Mayuan district and Zhujiahe and Nanrsquoanshan are ore deposits (spots) fromMiddle orezone of Mayuan district

Stage II Stage II is dominated by the widespread coarse-grained sphalerite Sp(b) and galena as well as minor amountof coarse-grained pyrite Py(b) Zn-Pbmineralization starts atstage I and continues with sphalerite impregnation followedby galena + sphalerite impregnation which subordinate stageII The cross-cutting relationships of stage I and stage II areobserved and shown in Figure 4(d) Stage II is themajormin-eralization stage for zinc and leadThismineralization stage ismost important in terms of tonnage andmining Major typesof ores include breccia-type vein-type (Figure 4(d)) andhigh-grade massive sulfide type (Figure 4(e)) with a simplemineralogy dominated by sphalerite galena and pyrite inthis stage Bitumen Bit(a) can also be observed in this stage(Figure 4(f)) occurring in vein-type and breccia-type oresand usually associating with contemporary sphalerite andgalena and gangue minerals such as dolomite calcite andquartz The Py(b) in this stage surrounded the Sp(b) orfilled the fractures of Sp(b) and galena grains (Figure 4(g))indicating a relatively late timing of formation

Stage III Stage III marked the end of hydrothermal ore-forming epoch and was characterized by quartz + barite +

calcite + bitumen Abundant bitumens Bit(b) in this stageare emulsion drops filling the open interspace between othergangue minerals and concentrated along crystal interface ofgangue minerals as well as microfissuring or pores (Figures4(h) and 4(i)) implying the bitumen might have formed alittle later than the gangue minerals

In the supergene stage oxide minerals include smith-sonite cerusite and limonite A paragenetic sequence forminerals in the Nanmushu Zn-Pb deposit is summarized inFigure 5

42 Fluid Inclusions Petrography and Laser Raman Spec-troscopic Analysis Samples of sphalerite (Sp(a) and Sp(b))dolomite quartz calcite and barite were selected from threehydrothermal stages in the Nanmushu deposit to determinethe nature of the fluids associated with mineralizationAbundant primary pseudosecondary and secondary FIsin these minerals are found In order to avoid erroneousinterpretations secondary FIs andor FIs which partiallydecrepitate during the microthermometric processes werenot documented during experiment FIs were studied insamples that are characterized with absence of plentiful

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

8 Geofluids

Bit(s)

Dol

Dol

(a)

Dol brecciaSp + Qz

Py(s)

2 cm

(b)

Qz + Sp(a)

Dol bre

ccia

Sp(b)

+ Qz

Bit(a)

1cm

(c)

Sp(a)

Sp(a)

Sp(b) + Gn

Sp(a)

Dol

Dol

(d)

Gn

Gn

Sp(b) Sp(b)

1cm

(e)

Bit(a)

Dol

SpSp

Dol

1 cm

(f)

Gn Py(b)

Sp(b)

Qz + Cal1 cm

(g)

Dol bre

ccia

Sp(b) + Gn

Brt + Cal + QzBit(b)

Bit(b)Sp

(b) + G

n

(h)

Dol

Dol

Qz

Bit(b)

1cm

(i)

Figure 4 Photographs of mineralization characteristics of the Nanmushu Zn-Pb deposit (a) Vein-type bitumen (Bit(s)) occurs parallel tothe country rock (b) Breccia-type ore dolomite breccia with Py(s) cemented by later hydrothermal mineral (c) Breccia-type ore yellowsphalerite + quartz (stage I) and brown sphalerite + quartz (stage II) are cemented by the dolomite breccia (d) Vein-type ore assemblagesof coarse-grained galena with minor sphalerite as a vein (stage II) crosscut the early sphalerite vein (stage I) (e) High-grade massive oreassemblages of coarse-grained galena and sphalerite (stage II) (f) Bit(a) associating with contemporary sphalerite occurs in vein (stage II)(g) Later Py(b) surround the early Sp(b) in stage II (h) Sphalerite and galena as breccia (stage II) cemented by late barite + calcite + quartz +bitumen (stage III) (i) Abundant Bit(b) filled in the interspace of quartz in stage III Bit bitumen Brt barite Cal calcite Dol dolomite Gngalena Py pyrite Qz quartz Sp sphalerite

Calcite

Pyrite

Smithsonite

Barite

Quartz

Dolomite

Sphalerite

Galena

Bitumen

Limonite

Cerusite

Pyrrhotite

MineralSedimentary

diageneticepoch

Hydrothermal epoch SupergeneepochStage IIIStage I Stage II

Figure 5 Paragenetic sequence for minerals in the Nanmushu Zn-Pb deposit Stage II is the main economic stage with abundant sphaleriteand galena

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

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Mining

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Journal of

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International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 9

Brt

６（2

６（2

（2

（2

（2

（2

（2

（2

（2

（2

10 m

10 m

10 m

20 m

６（2

６（2

６（2

６（2

６（2

６C（4

Bit

Cal

Dol

Qz

Qz

Sp

(a)

(c) (b)

(d) (e)

６（4+（2

20 m

Figure 6 Photomicrographs of typical FIs hosted in different minerals of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) A brown grain sphalerite contains abundant FIs including one relatively large type I FI (b) In an automorphic quartz grain thereare abundant type I and type II FIs which contain detectable bitumen (c) One type I FI with liquid + vapor phase in calcite (d) One two-phase CH4-rich inclusion in quartz is dominated by water with detectable methane (e) CH4-rich inclusions with dark bubbles are dominatedby detectable methane coexisting with type I FIs in barite Brt barite Cal calcite Dol dolomite Qz quartz Sp sphalerite

secondary inclusions trails and exhibit no evidence of posten-trapment modification (ie stretching leaking and neckingdown [25])

The majority of samples are dominated by primaryinclusions in terms of volume although small secondaryinclusions are easily observed Fluid inclusion morphologyin the samples studied varies from polyhedral to round andtheir sizes are generally ranging from 4 to 20120583m At roomtemperature (20∘C) most of FIs are two-phase (liquid +vapor) (Figure 6) In the order of decreasing abundance twocompositional types of FIs are distinguished(1) The first type is aqueous-salt dominant inclusions

(type I) which are found in all examined samples Type Iinclusions are about 6ndash18120583m on average but probably up to40 120583m in length and they are negative crystal ellipsoidalnear-spherical or irregular in shape (Figures 6(a) and 6(c))

The inclusions typically consist of liquid water and a water-dominated vapor phase which occupies 5 to 40 vol(2) The second type is hydrocarbon-bearing inclusions

(type II) which include three-phase hydrocarbon-bearinginclusions (liquid + vapor + solid phase with bitumen egFigure 6(b)) two phasesrsquo CH4-rich inclusions (Figure 6(d))one-phase CH4-rich inclusions (Figure 6(e)) and two phasesrsquooil-bearing inclusions (Figure 7) They are of ellipsoidalnear-spherical or irregular shapes and on average about6ndash25120583m in sizeThe inclusions typically have very consistentaqueous to carbonic phase ratios and fluorescent oil phasewas concentrated around gas bubbles (Figures 7(a) and 7(c))displaying consistent fluorescence colors within a particularcluster (Figure 7(f))

At stage I we observed abundant type I inclusions indolomite Sp(a) and quartz with size ranging from 3 to 18 120583m

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

10 Geofluids

10 m

(a)

10 m

(b)

10 m

(c)

10 m

(d)

10 m

(e)

10 m

(f)

Figure 7 Photomicrographs of hydrocarbon-bearing inclusions at room temperature (20∘C) ((a) (b)) Liquid-rich oil-bearing inclusioncomprises oil and gas The oil forms a yellow fluorescing (c) (d) Vapor-rich oil-bearing inclusion contains oil and gas The oil forms a thincream fluorescing rim around the hydrocarbon gas bubble ((e) (f)) A set of oil-bearing inclusions exhibit continuous different filling degrees(in yellow dotted line area) with yellow fluoresces coexisting with two-phase type I FIs and one-phase CH4-rich inclusions (in blue dashdotted line area) Note ((a) (c) (e)) under transmitted light crossed-nicols ((b) (d) (f)) under UV-epifluorescence

A smaller number of fluid inclusions contain hydrocarbon(type II) in this stage Not only CH4-bearing inclusionsare observed (determined by Laser Raman spectroscopicanalysis) but also oil-bearing inclusions with oil exhibitinga yellow to cream fluorescing rim around the hydrocarbonphase (Figures 7 8(a) and 8(b))

At stage II primary fluid inclusion assemblages occur asclusters of inclusions in gangueminerals including dolomitequartz and coarse-grained Sp(b) with growth zones Theyshow regular to negative crystal shape with the size varyingfrom 4 to 40 120583mNinety percent of these inclusions are type IA small number of type II inclusions in sphalerite containingconsiderable amounts of CH4 and bitumen were observedin our study through Laser Raman spectroscopic analysis(Figure 8(c))

At stage III type I inclusion occurs in quartz bariteand calcite with the size varying from 3 to 16 120583m This stagehas more type II inclusions than the two early stages (I andII) There are three-phase hydrocarbon-bearing inclusions(liquid + vapor + solid phase with bitumen) two phasesrsquoCH4-rich inclusions and one-phaseCH4-rich inclusionsThecompositions ofH2OCH4 C4H6 and bitumenwere detectedby Laser Raman spectroscopic analysis (Figures 8(d)ndash8(f))

43 Homogenization Temperature and Salinity The fluidinclusion microthermometry was based on the conceptof FIA [24] and microthermometric data were analyzedfrom two-three inclusions in each FIA There are aqueous-salt dominant inclusions (type I) and hydrocarbon-bearinginclusions (type II) in the Nanmushu deposit Figure 9shows typical FIAs in stages I II and III In our study weattempted measurements of type II inclusions in differentstages however only a few type II inclusions were measuredas a result of difficulties in observing the temperature (119879h) ofphase transition A limited number of CH4-rich inclusionsin quartz were measured for 119879h The CH4-rich inclusionsin quartz show 119879h values from minus139∘C to minus90∘C (to liquid)Within individual FIAs the ranges of 119879h are relatively smallfor example minus139∘C to minus135∘C minus91∘C to minus90∘C and minus118∘Cto minus120∘C The coexistence of the CH4-rich inclusions withtwo-phase inclusions in barite suggests fluid immiscibility(Figure 6(e)) The coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicates immiscibility andheterogeneous trapping (Figure 9(f)) As for a few two-phase inclusions with minor CH4 their homogenizationfrom liquid + vapor phase to liquid phase took place between142∘ and 165∘C

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 11

1500 2000 2500 3000 3500 4000

20000

40000

60000

80000

1000002911

Inte

nsity

Dol

10 m

Raman shift (cＧminus1)

（4

(a)

Inte

nsity

2912

1500 2000 2500 3000 3500 40006000

8000

10000

12000

Qz

10 m

Raman shift (cＧminus1)

（4

(b)

Inte

nsity

Bit

Sp

500 1000 1500 2000 2500 3000 3500 40000

10000

20000

30000

40000

1608

1329

2911

2926

1654

349

Sp

10 m

Raman shift (cＧminus1)

（4

(c)

Inte

nsity

2914

1500 2000 2500 3000 3500 4000

15000

20000

25000

30000

2914

Qz

10 m

Raman shift (cＧminus1)

（4

（4

（2

(d)

Inte

nsity Brt 2937

500 1000 1500 2000 2500 3000 3500 40000

20000

40000

60000

1648

2435

968

482Bit

10 m

Raman shift (cＧminus1)

4（6

(e)

Inte

nsity

Bit

1500 2000 2500 3000 3500 4000

10000

15000

200001605

1324

32102935

Qz

10 m

Raman shift (cＧminus1)

(f)

Figure 8 Representative Raman spectra of hydrocarbon-bearing inclusions for the Nanmushu Zn-Pb deposit Black line stands for theRaman spectra of hosted minerals while the red line represents the Raman spectra for FIs (a) CH4-rich inclusions in dolomite from stage I(b) CH4-rich inclusions in quartz from stage I (c) Hydrocarbon-bearing inclusions in sphalerite from stage II with CH4 and bitumen in thecarbonic phase (d) Hydrocarbon-bearing inclusions in quartz from stage III shows their vapor phase is composed of CH4 with their liquidphase containing H2O and CH4 (e) Hydrocarbon-bearing inclusions in barite from stage III with C4H6 and bitumen in the carbonic phase(f) Hydrocarbon-bearing inclusions in quartz from stage III with bitumen in the carbonic phase Brt barite Dol dolomite Qz quartz Spsphalerite

Type I inclusion as the predominant type was performedon various minerals from different stages and microther-mometric results are summarized in Table 2 and Figure 10(stage I Figures 10(a) and 10(b) stage II Figures 10(c) and10(d) stage III Figures 10(e) and 10(f))The firstmelting tem-peratures (119879m) melting temperature of hydrohalite (119879mHH)last ice-melting temperature (119879ice) and the temperature oftotal homogenization (119879h) have been measured in FIs hostedin dolomite calcite barite sphalerite and quartz Salinitiesare calculated as wt NaCl equivalent using 119879ice and the

equation of Roedder [12] and wt NaCl + CaCl2 equivalentusing 119879m 119879mHH and 119879ice by using the Software PackageFluids [16] At stage I we observed abundant type I inclusionswith measurements of homogenization (to liquid phase)temperatures of 171∘ to 340∘C for primary inclusions inquartz and 225∘ to 314∘C for inclusions in Sp(a) respectively(Table 2) Freezing experiments on type I inclusions in quartzyielded 119879m of minus207∘C corresponding to the stable eutecticmelting temperature (minus208∘C) of theH2O-NaCl system (eg[13 15]) However one type I inclusion in quartz yielded 119879m

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geology Advances in

12 Geofluids

(a-1)(a-2)

(a-3)

Qz

10 m

(a)

(b-1)

(b-2)

Sp

10 m

(b)

Qz10 m

minus170∘C

(c)

Qz10 m

minus145∘C

(d)

Qz10 m

minus90∘C

(e)

Liquid-onlyaqueous

inclusions

Gas inclusions

Gas inclusions

Gas-aqueous inclusions(heterogeneous trapping)

Qz10 m

(f)

Figure 9 Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit under transmitted light crossed-nicols (a) In stage I a trail of two-phase type I FIs (a-1 a-2 and a-3) in the quartz grain they have consistent vaporliquid ratiosMicrothermometry measurement shows that the ranges of histograms of total homogenization temperatures (119879h) of this FIA are relativelysmall for example 311∘C for (a-1) 302∘C for (a-2) and 308∘C for (a-3) respectivelyThey all homogenized to liquid phase Average temperature307∘C as 119879h of this FIA recorded in the result (b) In stage II a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistentvaporliquid ratios and similar119879h (255

∘C for (b-1) and 251∘C for (b-2) resp) Both of them homogenized to liquid phase Average temperature253∘C of this FIA recorded in the result ((c) (d) (e)) A trail of CH4-rich inclusions in quartz When the temperature decreases to minus190∘Cmost of one-phaseCH4-rich inclusionswere frozenWhen heated gradually this type inclusions appeared two-phase ((c) atminus170∘C) followedby the bubbles reduced ((d) at minus145∘C) and then homogenized to one liquid phase ((e) minus90∘C) (f) Coexistence of gas gas-aqueous andliquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping Qz quartz Sp sphalerite

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

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Mining

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Journal of

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International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 13

0

2

4

6

8

10

12

14

16

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage I

Sp(a)Qz

TＢ (∘C)

(a)

Sp(a)Qz

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage I

Salinity (wt NaCl equivalent)

(b)

0

5

10

15

20

25

30

35

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage II

Sp(b)Dol Qz

TＢ (∘C)

(c)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

yStage II

Salinity (wt NaCl equivalent)

Sp(b)Dol Qz

(d)

0

5

10

15

20

25

30

35

40

45

100 120 140 160 180 200 220 240 260 280 300 320 340

Freq

uenc

y

Stage III

QzBrtCal

TＢ (∘C)

(e)

0

2

4

6

8

10

12

14

16

18

2 4 6 8 10 12 14 16 18 20 22

Freq

uenc

y

Stage III

Salinity (wt NaCl equivalent)

QzBrtCal

(f)

Figure 10 Histograms of total homogenization temperatures (119879h) and salinities at different hydrothermal stages in the Nanmushu Zn-Pb deposit Brt barite Cal calcite Dol dolomite Qz quartz Sp(a) fine-grained sphalerite of hydrothermal stage I Sp(b) coarse-grainedsphalerite of hydrothermal stage II

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EarthquakesJournal of

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Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

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International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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MineralogyInternational Journal of

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MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

14 Geofluids

of minus313∘C which means it may contain other composition(eg CH4) 119879ice occurred between minus94

∘ and ndash24∘C in quartzand minus78∘ and ndash38∘C in Sp(a) corresponding to salinitiesof 40ndash133 and 62ndash112 wt NaCl equivalent respectively(Table 2 Figure 10(b))

At stage II first melting temperature (119879m) was observedin a single type I inclusion in quartz atminus587∘C indicating thepresence of CaCl2 in addition toNaCl (eg [12 27])119879m of theinclusions in Sp(b) ranges from minus347∘ to minus213∘C which aretypical characteristics for the H2O-NaCl plusmn CaCl2 plusmn MgCl2system [12 15 27 28] When heated gradually 119879m wasfollowed by the melting of hydrohalite (119879mHH) and then lastice-melting temperature (119879ice) We attempted measurementsof the temperatures of phase transition of hydrohalite (119879mHH)in each FIA but it was difficult to observe Only a fewinclusions in quartz observed 119879mHH values range of minus272∘ tominus213∘C and 119879ice values range of minus75

∘ to minus36∘C Assuminga system of H2O-NaCl-CaCl2 NaCl(NaCl + CaCl2) ratiosand compositions in wt NaCl + CaCl2 equivalent werecalculated from 119879mHH and 119879mice using the Software PackageFluids of Steele-MacInnis et al [16]The values ofNaCl(NaCl+ CaCl2) ratios range from 04 to 10 The salinities are 61 to115 wt NaCl + CaCl2 equivalent including 49ndash104 wtNaCl equivalent and 02ndash65 wt CaCl2 equivalent

Fluid inclusions in quartz have 119879h values of 186∘ to 264∘C

and119879ice values of minus103∘ to minus28∘C corresponding to salinities

of 47 to 143 wt NaCl equivalent Dolomite-hosted fluidinclusions share similar 119879h values of 152∘ndash265∘C and 119879icevalues from minus83∘ to minus12∘C corresponding to salinities of59 to 133 wt NaCl equivalent Sp(b) that is associated withquartz and dolomite has inclusions with Th values of 183∘ to276∘C and 119879ice values of minus94

∘ to minus36∘C corresponding tosalinities of 20 to 122 wt NaCl equivalent (Figures 10(c)and 10(d))

At stage III fluid inclusions have 119879h values of 107∘ to202∘C and 119879ice values of minus154

∘ to minus12∘C corresponding tosalinities of 21 to 190wtNaCl equivalent (Figures 10(e) and10(f)) When the temperature deceases to minus100∘C the liquidphase of some type I inclusion was yellowish in color whichis characteristic for the eutectic composition of the H2O-NaCl-CaCl2 system (eg [4 17]) The 119879m (ndash516∘ to ndash513∘C)and 119879mHH (ndash370∘C) were observed in barite supporting theH2O-NaCl-CaCl2 plusmn MgCl2 system Assuming a system ofH2O-NaCl-CaCl2 salinities of 116ndash148 wt NaCl + CaCl2equivalent were calculated by using the Software PackageFluids [16] based on the values of 119879m 119879mHH and 119879mice

44 Sulfur Isotopic Composition The 12057534S values of the ana-lyzed sulfides are summarized in Table 3 Sulfur isotope datain this study were combined with previous published datafrom the Nanmushu deposit (Figure 11 [7 9 17]) and otherdeposits (eg Kongxigou depositWang et al [7] Nananshandeposit Hou et al [17]) in theMayuan district Sulfur isotopiccompositions of six sphalerite samples from the same stage IIbut different locality that was stated above have a narrow 12057534Srange of +174 to +183permil which are similar to those previousdata at Nanmushu deposit between +119 and +239permil [7 917] (Table 3) The sphalerite in the Kongxigou deposit shows

0

2

4

6

8

10

12

14

16

18

20

11 13 15 17 19 21 31 33 35

BariteGalena Sphalerite

Pyrite

Freq

uenc

y

34３ (₀)

Figure 11 Histogram of sulfur isotopic compositions of sulfides andsulfate from theMayuan district (data sourcesWang et al 2008 [7]Li et al 2007 [9] Hou et al 2007 [17] and this study)

12057534S value of +160permil[7] and galena in theNananshandepositat Mayuan shows 12057534S value of +129permil [7] In additionbarites from the Nanmushu deposit and the Zhujiahe oreprospect have nearly the same 12057534S values of +322permil and+333 to +335permil respectively [17]

5 Discussion

51 Nature of the Ore-Forming Fluids Previous publishedfluid inclusion microthermometric data from the Mayuandistrict are limited to the work of Hou et al [17] and Liu etal [8] Hou et al [17] analyzed five samples from Mayuandistrict with result of homogenization temperatures rangingfrom 130∘ to 210∘C but without detailed sample descriptionand fluid inclusion petrography Liu et al [8] reportedmicrothermometric measurements only from quartz andcalcite and no data on other minerals for example dolomitebarite and sphalerite Their results show homogenizationtemperatures of 98∘ to 337∘C (typically range from 150∘ to300∘C) and salinities of 77 to 222 wt NaCl equivalent

In this study systematic petrographic and microthermo-metric data have been carried out andmeasurements of fluidinclusions in different stages and minerals in the NanmushuZn-Pb deposit have been presented in Table 2 and Figure 10Aqueous-salt dominant inclusions (type I) in the Nanmushudeposit illustrate that they contain medium-low temperature(107∘ to 340∘C) and medium-high salinity (up to 19wtNaCl equivalent) brines (Table 2) Such fluids with thisnature are universal in sedimentary basins and are frequentlyassociated with sedimentary hosted Zn-Pb deposits (eg [1429]) In addition hydrocarbon-bearing inclusions (type II)are easily observed on three hydrothermal stages occurringas three-phase hydrocarbon-bearing inclusions (liquid +vapor + solid phase with bitumen eg Figure 6(b)) twophasesrsquo CH4-rich inclusions (Figure 6(d)) one-phase CH4-rich inclusions (Figure 6(e)) or two phasesrsquo oil-bearing

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MineralogyInternational Journal of

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Geological ResearchJournal of

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Geology Advances in

Geofluids 15

inclusions (Figure 7) The similar characteristics are alsofound in some sedimentary rock hosted Zn-Pb depositswhich are located inaround sedimentary basins worldwide[29ndash32] According to the discussion above and geologicallocation (eg near Sichuan Basin) of the Nanmushu Zn-Pbdeposit we propose that the ore-forming fluids are basinalbrines As the features of ore-forming fluids (medium-low temperature medium-high salinity with hydrocarbon)brines of sedimentary basins were thought to supply ore-forming materials and contribute to the mineralization

The presence of hydrocarbon-bearing inclusions andbitumen especially widely distributed CH4-rich inclusionsdemonstrates that there were extensive hydrocarbon activ-ities in the Nanmushu deposit In general the CH4-richhydrothermal fluids may come from three ultimate sources(1) abiogenic origin derived from the mantle [33 34] (2)abiogenic origin derived from postmagmatic alteration byFischerndashTropsch type synthesis [35ndash37] (3) incorporationof thermally decomposed organic material (thermogenesis)orand products from microbial processes (bacteriogene-sis) [38ndash41] The deposit characteristics (without postmag-matic alteration) and sulfur isotope characteristics excludedthe abiogenic origin LRM results show CH4-bearing fluidinclusions commonly existed in sphalerite dolomite quartzand barite illustrating that these minerals were precipitatedfrom a common methane-rich ore-forming fluid As fluo-rescence effect of organic materials may mislead the analysisonly CH4 Raman peaks can generally be detected above thehigh background (Figure 8) In addition the 12057513C values forCH4 in fluid inclusions are ndash372permil and ndash281permil in quartz andndash210permil to ndash237permil in barite [8] These extremely negative12057513C values suggest that an isotopically light carbon sourcecontributed to the ore-forming fluids Thus the organic ori-gin may be a reasonable mechanism to explain the abundantCH4-rich inclusions

52 Origin of the Sulfur Asmany important sulfur reservoirshave distinct sulfur isotopic signature the 12057534S values canbe used as representative of the sulfur sources [42] The12057534S values of the sulfides show a relatively narrow range(Figure 11 Table 3) but significantly different from thoseof mantle-derived magmatic sulfur (around 0permil [43]) The12057534S values of sulfides in the Nanmushu deposit are slightlylower than those of evaporites in the Cambrian to Triassicstrata (+15 to +35permil [44]) and the seawater sulfates of theNeoproterozoic Dengying Formation (+20 to +39permil [45])However the 12057534S value of barite in the Nanmushu depositis 322permil [17] similar to those of evaporites in the Cambrianto Triassic strata or seawater sulfates of the NeoproterozoicDengying Formation

The 12057534S values of sulfides from the Nanmushu depositsuggest that the sulfur was likely to be derived from SO4

2minus

reduction from seawater andor evaporitic sulfates that havepossibly been leached by basinal brines during mineraliza-tion In consideration of temperatures of FIs in the Sp(a) andSp(b) at the range of 183∘ndash314∘C the possible mechanism forreduced sulfur is thermochemical sulfate reduction (TSR)because TSR can occur under high temperatures while

bacterial sulfate reduction (BSR) can only take place underlow temperatures (lt127∘C) [38 46] In addition TSR wouldlike to produce a series of organicmatter (eg bitumenC3H8C2H6 and CH4) [38 40 46 47] Ore-forming fluids showan increase in carbonaceous contents over time In stage Iquartz-hosted fluid inclusions with CH4 in volatile and someoil-bearing inclusions occur In stage II CH4-rich inclusionsare relatively widespread which occur not only in gangueminerals but also in sphalerite Moreover carbonic phase insphalerite also includes bitumen In stage III the increasingamount and species of hydrocarbon-bearing inclusions (egCH4 C4H6 and bitumen) are consistent with changingfluid composition which is likely caused by TSR duringmineralization

Therefore it is reasonable to suggest that the positive12057534S values (+156 to +194permil) in the Nanmushu Zn-Pbdeposit were resulted from TSR This phenomenon agreeswell with geologic and FIs characteristics in the Nanmushudeposit which show occurrence of organic matter includingbitumen in mineralization stages (Figure 4) and abundantcarbonaceous contents in hydrocarbon-bearing inclusions(Figures 6 7 and 9) TSR-related chemical reactions mayhappen [38 46]

CH4 + SO42minus 997888rarr CO3

2minus +H2S + 2H2O (1)

Hydrocarbons + CaSO4 rarr altered hydrocarbons + solidbitumen + CaCO3 + H2S + H2O TSR-related reduced sulfur(eg H2S) could have been involved in the ore-formingprocess with chemical reactions

Zn2+ +H2S 997888rarr ZnSdarr (sphalerite) + 2H+

Pb2+ +H2S 997888rarr PbSdarr (galena) + 2H+(2)

They are responsible for the deposition of sphalerite andgalena in the ore-forming processes

53 Evolution of the Ore-Forming Fluids In the Nanmu-shu Zn-Pb deposit microthermometry and Laser Ramanspectroscopic analyses for fluid inclusions have identifiedamounts of salts (mainly NaClmixed with CaCl2 andMgCl2)and carbonaceous contents (mainly CH4 C4H6 and bitu-men Figure 8) in fluids Hydrocarbon-bearing inclusionshave changeable liquidvapor ratios Oil-bearing inclusionsexhibit continuous different filling degrees with yellow flu-oresces (Figure 6) They typically occur together with onlyvapor hydrocarbon phase CH4 inclusions and aqueous-saltinclusions (Figures 6 and 7) The coexistence of gas (CH4)gas-aqueous and liquid-only inclusions was also observed(Figure 9) Such phenomenon provides evidence that thefluid system of the Nanmushu Zn-Pb deposit consisted of anaqueous-salt solution and an immiscible hydrocarbon phase(eg [3 4 48])

Temperatures of FIs exhibit a decreasing trend fromstage I to stage III (Table 2 Figures 10 and 12) Salinitiesof stage I (43 to 133 wt NaCl equivalent) stage II (20to 143 wt NaCl equivalent) and stage III (21 to 190 wtNaCl equivalent) are similar (Figures 10 and 12) Notably FIs

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

16 Geofluids

100

150

200

250

300

350

400

0 5 10 15 20 25Salinity (wt NaCl equivalent)

Stage I

Stage II

Stage III

FIs from stage IFIs from stage IIFIs from stage III

TＢ(∘

C)

Figure 12 Total homogenization temperatures versus salinitiesdiagram for the three hydrothermal stages showing fluid evolutionof the Nanmushu Zn-Pb deposit

hosted in the barite which were only found at stage III havethe relatively high salinities (up to 190 wt NaCl equivalentTable 2) On the basis of ore-forming fluids characteristicsin the Nanmushu Zn-Pb deposit (Figures 10 and 12) thedecoupling between the temperature and salinity in fluidsmay suggest that there was an addition of external fluidwith higher salinity (with CaCl2 plusmn MgCl2-enriched) flowinto the relatively lower salinity primary fluid system duringmineralization of this deposit

In hydrothermal stage I the originalH2O-NaCl fluidwithmethane enrichment is predominately in the fluid systemwith a small quantity of later fluid into the connatural fluidsystem Temperature of FIs shows a distinct bimodal withmaxima at around 180∘ and 300∘C (Figure 10(a)) probablybecause of the original fluid and later external fluid withdifference temperatures andor heterogeneous trapping FIAswith wide ranges of Th values in stage I imply heterogeneoustrapping accompanied by immiscibility of hydrocarbonphase and aqueous-salt solution

In stage II with adding an increasing amount of highersalinity CaCl2 plusmn MgCl2-rich brine the temperatures of FIscontinuously decreased and the salinities of the fluid systemcan reach up to 143 wt NaCl equivalent (Figure 12 andTable 2) CH4-rich inclusions appear not only in gangueminerals but also in sphalerite Hydrocarbon-bearing inclu-sions in sphalerite with CH4 and bitumen in the carbonicphase were detected by Laser Raman spectroscopic analysis(Figure 8)

In stage III owing to the continuous addition of theextraneous fluid temperature of fluid became lower with itssalinities rising inversely (Table 2 Figure 12) Higher numberspecies of CH4 C4H6 and bitumen were detected in thecarbonic phase of hydrocarbon-bearing inclusions (Figure 8)

The presence of CH4-rich inclusions in each hydrother-mal stage (Table 2 and Figure 8) suggests that the originalfluids contain abundant hydrocarbons The hydrocarbonsmay react with sulfates to produce a series of organic matterthrough TSR Thus ore-forming fluids show an increasein carbonaceous contents and species It implies that the

hydrocarbons were entrained with the hydrothermal fluidsthroughout the paragenetic sequence during mineralizationBitumen associatedwith contemporary sphalerite vein occursin stage II (Figure 4) In the main stage sphalerite andquartz primary hydrocarbon-bearing inclusions containingbitumen also were observed and detected (Figures 4 and 8)These characteristics strongly suggest an intimate relation-ship between bitumen and mineralization

Although PVTX modelling and equations of fluid inclu-sion from simultaneously and homogeneously entrappedFIAs can be used to estimate fluid pressures when irre-versible physical and chemical changes happened the PVTXmodelling and equations are invalid Based on the forego-ing discussion the fluid system of the Nanmushu Zn-Pbdeposit is a heterogenous fluid system which consisted of anaqueous-salt solution and an immiscible hydrocarbon phaseHowever TSR is an irreversible process [38] When solidbitumen as hydrocarbon phase appears in the hydrocarbon-bearing inclusions it implies that irreversible physical andchemical changes happened in the closed system of thehydrocarbon inclusions [15] Actually TSR and solid bitumenas hydrocarbon phase in the hydrocarbon-bearing inclusionsboth exist in the Nanmushu Zn-Pb deposit Taking theseinto account it seems there are no appropriate FIAs tocalculating pressure on account of complex fluid system inthe Nanmushu Zn-Pb deposit

54 Genetic Type of theDeposit Ore genesis of theNanmushuZn-Pb deposit has been discussed since it was first discoveredin 2004 In spite of the orebodies generally controlled bystratum and structure the occurrence of abundant vein-typeand breccia-type ores shows that hydrothermal activity iscritical for themineralizationOre-forming fluids in theNan-mushu deposit are medium-low temperature (107∘ndash340∘C)and medium-high salinity (up to 19wt NaCl equivalent)brines with carbonaceous components of CH4 C4H6 andbitumen concentrations similar to those of basinal brine sys-temswith hydrocarbonsworldwide [49ndash51] LowerCambrianGuojiaba Formation carbonaceous slate may have acted as acapping aquitard for mineralizing fluids flowing through themore permeable sandstone and dolomite

The sphalerites from the sediment-hosted Zn-Pb ores atthe Mayuan district have been dated with a Rb-Sr isochronage of 486 plusmn 12Ma (Ordovician Li et al [9]) RecentlyHan et al [10] collected the later hydrothermal bitumen andobtained a bitumen Re-Os isochron age of 128plusmn8Ma In thisdeposit three generations of bitumen have been observedincluding Bit(s) Bit(a) and Bit(b) that have distinctive asso-ciation of minerals and textures The Bit(s) formed duringsedimentary diagenetic stage far from the orebody and theyoccur parallel to the country rock beddings and fracturesTheBit(a) formed during mineralization of the main economicstage II Post-ore Bit(b) formed later than the ganguemineralsof stage III or even later than the whole mineralization stagesBased on the sample descriptions of Li et al [9] and Hanet al [10] and the petrography observations of our studywe regard that ca486Ma for sphalerite (Sp(b)) representsthe major mineralization age of stage II and ca128Ma forbitumen (Bit(b)) formed during post-ore stage Both of them

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 17

are much younger than the sedimentation age of the hostNeoproterozoic Dengying Formation (sim540Ma [52]) Themineralization of the Nanmushu deposit located in thenorthern Yangtze Block may have lasted for a prolongedperiod The obtained ages fall in the range between Caledo-nian orogeny and Indosinian-Yanshanian movement whichboth have been regarded as the two main mineralizationevents in the Yangtze Block Compaction and topographicallydriven fluid flows are the likelymechanisms in theNanmushuZn-Pb deposit Sediment compaction probably occurredduring the Neoproterozoic to Permian that caused thickcover sequence (over 9 km) and major sedimentation in thebasin while the basin compression and topographic reliefoccurred during the Indosinian-Yanshanian movement Theforeland basin system of the northern Yangtze plate recordsthe intracontinental tectonic deformation and oblique amal-gamation of the Yangtze and North China-Qinling-Dabiecomplex plates during the late Triassic (late Indosinian) toprobably early Jurassic (early Yanshanian) [53]The northernSichuan basins were filled by the depositional system andtheMicangshan fold-and-thrust belt belonged to the forelandbelt It is noted that theNanmushuZn-Pb deposit occurs nearnorthern Sichuan Basin and the Micangshan fold-and-thrustbeltTherefore the aforementioned tectonicmovement couldhave driven the large-scale flow of basinal brines carryingore-forming metals to migrate a long distance which was inresponse to the Nanmushu Zn-Pb deposit mineralization

In the Sichuan basins the Pb-Zn deposits and paleo-oil-gas reservoirs show a closed spatial distribution and they arepossibly controlled by the basinal fluid flow [47 54] Thecompressional tectonic event may influence the Chipu Pb-Zn deposit and the gas reservoir hosted in the DengyingFormation may contribute to mineralization [54] It is notedthat the Chipu Pb-Zn deposit has abundant organic matterand is hosted within the Dengying Formation similar tothe Namushu Zn-Pb deposit We speculate organic matterin the Namushu Zn-Pb deposit possibly came from a paleo-oil-gas reservoir on andor near the sites of the NanmushuZn-Pb deposit Given geological geochemical and fluidinclusion characteristics mentioned above for the NanmushuZn-Pb deposit it is consistent with typical MVT depositsThey are epigenetic deposits which are hosted in carbonate-dominated sedimentary rocks generally stratabound andstratiform with sulfide minerals replacing carbonates andfilling open spaces in the host rocks [29 55] Most of theworldrsquos MVT Zn-Pb deposits occur in orogenic forelandsand mineralizations are accompanied by tectonic movement[29 56] In addition many of typical MVT deposits havelow-moderate temperatures and medium salinities of basinalbrines with abundant hydrocarbons [29] which are consis-tent with the Nanmushu deposit studied here Therefore wesuggest that the Nanmushu deposit is a MVT Zn-Pb deposit

6 Conclusions

The Nanmushu deposit is a MVT Zn-Pb deposit andthe mineralization contains three stages (1) sedimentarydiagenetic stage (2) hydrothermal ore-forming stage withthree substages (I II and III) and (3) supergene stage The

hydrothermal stage II is the main economic mineralizationstage

The 12057534S values of sulfides in the Nanmushu depositare characterized by positive values with a peak around+18permil and the reduced sulfur may have derived fromreduction of SO4

2minus from seawater andor evaporitic sulfatesThermochemical sulfate reduction (TSR) is the likely keyfactor for sulfur isotope fractionation during the ore-formingprocesses

Ore-forming fluids are basinal brines trapped in a het-erogenous fluid system with medium-low temperature (107∘to 340∘C) and medium-high salinity (up to 19wt NaClequivalent) The majority of fluid inclusions are aqueous-salt dominant inclusions (type I) with minor hydrocarbon-bearing inclusions (type II) with amount of CH4 C4H6and bitumen Microthermometric data exhibit temperaturecontinuously decreased (171 to 340∘C in stage I 152 to 276∘Cin stage II and 107 to 202∘C in stage III) however thesalinities maintain approximately the same at around 6 to12wt NaCl equivalent in the two major ore-forming stages(I and II) and the salinities of barite-hosted FIs in stage IIIshow a slight increase up to 190 wt NaCl equivalent Thesefeatures suggest a mixing of higher salinity CaCl2 plusmn MgCl2-rich fluids into the original H2O-NaCl with methane-richfluid systemDifferent temperature-salinity fluidsmixing andTSR could be the predominant factors to control the Zn-Pbmineralization in the Nanmushu deposit

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

This research was supported by projects from the NationalNatural Science Foundation of China (41603042 and41672140) China Geological Survey (121201103094200)and the Fundamental Research Funds for the CentralUniversities China University of Geosciences Wuhan(CUGQYZX1733) The authors are grateful to Mr Ying Maand Qi-Zhi Chen and Dr Man-Rong Jiang for helping withsample preparation and Professor Mou-Chun He for helpingwith Laser Raman spectroscopy analysis

References

[1] J S Leventhal ldquoOrganic matter and thermochemical sulfatereduction in the Viburnum Trend southeast Missourirdquo Eco-nomic Geology vol 85 no 3 pp 622ndash632 1990

[2] P F Greenwood J J Brocks K Grice et al ldquoOrganic geo-chemistry andmineralogy I Characterisation of organicmatterassociated with metal depositsrdquo Ore Geology Reviews vol 50pp 1ndash27 2013

[3] X X Gu Y M Zhang B H Li S Y Dong C J Xue andS H Fu ldquoHydrocarbon- and ore-bearing basinal fluids Apossible link between gold mineralization and hydrocarbonaccumulation in the Youjiang basin South ChinardquoMineraliumDeposita vol 47 no 6 pp 663ndash682 2012

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

18 Geofluids

[4] GChi C Xue X Sun et al ldquoFormation of a giant Zn-Pbdepositfrom hot brines injecting into a shallow oil-gas reservoir insandstones Jinding southwestern Chinardquo Terra Nova vol 29no 5 pp 312ndash320 2017

[5] W Qi M T Hou K M Wang and D G Wang ldquoA large-scale stratabound lead-zinc metallogenic belt discovered in theMayuan areardquo Regional Geology of China vol 23 pp 1139ndash11422004 (Chinese)

[6] B Y Chen R X Li H Q Liu Y N Zhang and S WLiu ldquoGeochemical charecteristics of Dengying dolomite in theMayuan lead-zinc orefield Nanzheng Shaanxirdquo Bulletin andMineralogy Petrology and Geochemistry vol 33 pp 193ndash2002014 (Chinese)

[7] H XWang J C Xue ZM Li Q Li and R J Yang ldquoGeologicaland geochemical characteristics of Mayuan Pb-Zn ore depositon northernmargin of Yangtze landmassrdquoMineralDeposits vol27 pp 37ndash48 2008 (Chinese)

[8] S Liu R Li G Chi R Zeng L Liu and S Shi ldquoGeo-chemical Characteristics and Sources of Ore-forming Fluids ofthe Mayuan Pb-Zn Deposit Nanzheng Shaanxi Chinardquo ActaGeologica Sinica vol 89 no 3 pp 783ndash793 2015

[9] H-M Li Y-C ChenD-HWang andH-Q Li ldquoGeochemistryand mineralization age of the Mayuan zinc deposit Nanzhengsouthern Shaanxi Chinardquo Geological Bulletin of China vol 26no 5 pp 546ndash552 2007 (Chinese)

[10] Y Han Y Liu S Liu et al ldquoOrigin of the breccia andmetallogenic geological background ofMayuan Pb-Zn depositrdquoEarth Science Frontiers vol 23 no 4 pp 94ndash101 2016

[11] Y B Gao K Li B QianW Y LiM C Zheng and C G ZhangldquoTrace elements S Pb He Ar andC isotopes of sphalerite in theMayuan Pb-Zn deposit at the northern margin of the Yangtzeplate Chinardquo Acta Petrologica Sinica vol 32 pp 251ndash263 2016(Chinese)

[12] E Roedder ldquoFluid inclusionsrdquo Reviews in Mineralogy vol 12pp 1ndash644 1984

[13] R J Bodnar ldquoRevised equation and table for determining thefreezing point depression of H2O-Nacl solutionsrdquo Geochimicaet Cosmochimica Acta vol 57 no 3 pp 683-684 1993

[14] J J Wilkinson ldquoFluid inclusions in hydrothermal ore depositsrdquoLithos vol 55 no 1-4 pp 229ndash272 2001

[15] H Z Lu H R Fan P Ni G X Ou K Shen and W H ZhangFluid inclusion Science Press Beijing China 2004

[16] M Steele-MacInnis R J Bodnar and J Naden ldquoNumericalmodel to determine the composition of H2O-NaCl-CaCl2 fluidinclusions based on microthermometric and microanalyticaldatardquo Geochimica et Cosmochimica Acta vol 75 no 1 pp 21ndash40 2011

[17] M T Hou D G Wang S B Deng and Z R Yang ldquoGeologyand genesis of the Mayuan lead-zinc mineralization belt in theShaanxi Provincerdquo Northwestern Geology vol 40 pp 42ndash602007

[18] H C Liu and W D Lin Study on the law of PbndashZnndashAg oredeposit in Northeast Yunnan China Yunnan University PressKunming China 1999

[19] W-H Sun M-F Zhou J-F Gao Y-H Yang X-F Zhaoand J-H Zhao ldquoDetrital zircon U-Pb geochronological andLu-Hf isotopic constraints on the Precambrian magmatic andcrustal evolution of the western Yangtze Block SW ChinardquoPrecambrian Research vol 172 no 1-2 pp 99ndash126 2009

[20] X-F Zhao M-F Zhou J-W Li et al ldquoLate Paleoproterozoicto early Mesoproterozoic Dongchuan Group in Yunnan SW

China Implications for tectonic evolution of theYangtze BlockrdquoPrecambrian Research vol 182 no 1-2 pp 57ndash69 2010

[21] S Gao J Yang L Zhou et al ldquoAge and growth of the ArcheanKongling terrain South China with emphasis on 33 GAgranitoid gneissesrdquo American Journal of Science vol 311 no 2pp 153ndash182 2011

[22] C Zhang Y Wu L Hou and J Mao ldquoGeodynamic set-ting of mineralization of Mississippi Valley-type deposits inworld-class Sichuan-Yunnan-Guizhou Zn-Pb triangle south-west China Implications from age-dating studies in the pastdecade and the Sm-Nd age of Jinshachang depositrdquo Journal ofAsian Earth Sciences vol 103 pp 103ndash114 2015

[23] M T Hou D G Wang Z R Yang and J Gao ldquoGeologicalcharacteristics of lead-zinc mineralized zones in the Mayuanarea Shaanxi and their ore prospectsrdquo Geology in China vol34 pp 101ndash109 2007

[24] R H Goldstein ldquoPetrographic analysis of fluid inclusionrdquoMinerallogical Association of Canada Short Course Handbookvol 32 pp 9ndash54 2003

[25] R J Bodnar ldquoReequilibration of fluid inclusionsrdquo in Fluidinclusions Analysis and Interpretation I Samson A Andersonand D Marshall Eds vol 32 of Mineralogical Association ofCanada Short Course Series pp 213ndash230 2003

[26] E A J Burke ldquoRaman microspectrometry of fluid inclusionsrdquoLithos vol 55 no 1-4 pp 139ndash158 2001

[27] R H Goldstein and T J Reynolds Systematics of Fluid Inclu-sions in Diagenetic Minerals SEPM (Society for SedimentaryGeology) 1994

[28] C S Oakes R J Bodnar and J M Simonson ldquoThe systemNaClCaCl2H2O I The ice liquidus at 1 atm total pressurerdquoGeochimica et Cosmochimica Acta vol 54 no 3 pp 603ndash6101990

[29] D L Leach D C Bradley D Huston S A Pisarevsky R DTaylor and S J Gardoll ldquoSediment-hosted lead-zinc depositsin earth historyrdquo Economic Geology vol 105 no 3 pp 593ndash6252010

[30] S A Gleeson J J Wilkinson F M Stuart and D A BanksldquoThe origin and evolution of base metal mineralising brinesand hydrothermal fluids South Cornwall UKrdquo Geochimica etCosmochimica Acta vol 65 no 13 pp 2067ndash2079 2001

[31] R Thiery ldquoThermodynamic modelling of aqueous CH4-bearing fluid inclusions trapped in hydrocarbon-rich environ-mentsrdquo Chemical Geology vol 227 no 3-4 pp 154ndash164 2006

[32] J Conliffe D H C Wilton N J F Blamey and S MArchibald ldquoPaleoproterozoic Mississippi Valley Type Pb-Znmineralization in the RamahGroup Northern Labrador Stableisotope fluid inclusion and quantitative fluid inclusion gasanalysesrdquo Chemical Geology vol 362 pp 211ndash223 2013

[33] B S Lollar G Lacrampe-Couloume G F Slater et al ldquoUnrav-elling abiogenic and biogenic sources of methane in the Earthrsquosdeep subsurfacerdquo Chemical Geology vol 226 no 3-4 pp 328ndash339 2006

[34] B S Lollar G Lacrampe-Couloume K Voglesonger T COnstott L M Pratt and G F Slater ldquoIsotopic signatures ofCH4 and higher hydrocarbon gases from Precambrian Shieldsites A model for abiogenic polymerization of hydrocarbonsrdquoGeochimica et CosmochimicaActa vol 72 no 19 pp 4778ndash47952008

[35] S Salvi and A E Williams-Jones ldquoFischer-Tropsch synthesis ofhydrocarbons during sub-solidus alteration of the strange lakeperalkaline granite QuebecLabrador Canadardquo Geochimica etCosmochimica Acta vol 61 no 1 pp 83ndash98 1997

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Geofluids 19

[36] J Potter A H Rankin and P J Treloar ldquoAbiogenic Fischer-Tropsch synthesis of hydrocarbons in alkaline igneous rocksfluid inclusion textural and isotopic evidence from theLovozero complex NW Russiardquo Lithos vol 75 no 3-4 pp 311ndash330 2004

[37] Y A Taran G A Kliger and V S Sevastianov ldquoCarbonisotope effects in the open-system Fischer-Tropsch synthesisrdquoGeochimica et CosmochimicaActa vol 71 no 18 pp 4474ndash44872007

[38] PMouginV Lamoureux-VarA Bariteau andAYHuc ldquoTher-modynamic of thermochemical sulphate reductionrdquo Journal ofPetroleum Science and Engineering vol 58 no 3-4 pp 413ndash4272007

[39] N I Basuki B E Taylor and E T C Spooner ldquoSulfur isotopeevidence for thermochemical reduction of dissolved sulfate inMississippi Valley-type zinc-lead mineralization Bongara areaNorthern Perurdquo Economic Geology vol 103 no 4 pp 783ndash7992008

[40] U Herlec J E Spangenberg and J V Lavric ldquoSulfur isotopevariations from orebody to hand-specimen scale at the Mezicalead-zinc deposit Slovenia A predominantly biogenic patternrdquoMineralium Deposita vol 45 no 6 pp 531ndash547 2010

[41] J Carrillo-Rosua A J Boyce S Morales-Ruano et alldquoExtremely negative and inhomogeneous sulfur isotope sig-natures in Cretaceous Chilean manto-type Cu-(Ag) depositsCoastal Range of central Chilerdquo Ore Geology Reviews vol 56pp 13ndash24 2014

[42] H Ohmoto and R O Rye ldquoIsotopes of sulfur and carbonrdquo inGeochemistry of Hydrothermal Ore Deposits H L Barnes Edpp 509ndash567 Wiley New York NY USA 2nd edition 1979

[43] M Chaussidon F Albarede and S M F Sheppard ldquoSulphurisotope variations in the mantle from ion microprobe analysesof micro-sulphide inclusionsrdquo Earth and Planetary ScienceLetters vol 92 no 2 pp 144ndash156 1989

[44] G E Claypool W T Holser I R Kaplan H Sakai and I ZakldquoThe age curves of sulfur and oxygen isotopes in marine sulfateand their mutual interpretationrdquo Chemical Geology vol 28 pp199ndash260 1980

[45] T Zhang X Chu Q Zhang L Feng and W Huo ldquoThe sulfurand carbon isotopic records in carbonates of the DengyingFormation in the Yangtze Platform Chinardquo Acta PetrologicaSinica vol 20 no 3 pp 717ndash724 2004

[46] H G Machel ldquoBacterial and thermochemical sulfate reductionin diagenetic settings - old and new insightsrdquo SedimentaryGeology vol 140 no 1-2 pp 143ndash175 2001

[47] J-X Zhou J-H Bai Z-L Huang D Zhu Z-F Yan and Z-C Lv ldquoGeology isotope geochemistry and geochronology ofthe Jinshachang carbonate-hosted Pb-Zn deposit southwestChinardquo Journal of Asian Earth Sciences vol 98 pp 272ndash2842015

[48] G M Anderson ldquoThe mixing hypothesis and the origin ofMississippi valley-type ore depositsrdquo Economic Geology vol103 no 8 pp 1683ndash1690 2008

[49] D L Leach D Bradley M T Lewchuk D T A Symons GDe Marsily and J Brannon ldquoMississippi Valley-type lead-zincdeposits through geological time Implications from recent age-dating researchrdquo Mineralium Deposita vol 36 no 8 pp 711ndash740 2001

[50] S E Kesler M Reich and M Jean ldquoGeochemistry of fluidinclusion brines from Earthrsquos oldest Mississippi Valley-type(MVT) deposits Transvaal Supergroup South Africardquo Chem-ical Geology vol 237 no 3-4 pp 274ndash288 2007

[51] M S Appold and Z J Wenz ldquoComposition of ore fluidinclusions from the Viburnum Trend Southeast Missouri dis-trict United States Implications for transport and precipitationmechanismsrdquo Economic Geology vol 106 no 1 pp 55ndash78 2011

[52] Y L Chen X L Chu X L Zhang andM G Zhai ldquoCarbon iso-topes sulfur isotopes and trace elements of the dolomites fromthe Dengying Formation in Zhenba area southern ShaanxiImplications for shallow water redox conditions during theterminal Ediacaranrdquo Science China Earth Sciences vol 58 no7 pp 1107ndash1122 2015

[53] T Qian S Liu W Li T Gao and X Chen ldquoEarly-MiddleJurassic evolution of the northern Yangtze foreland basin Arecord of uplift following Triassic continent-continent collisionto form the Qinling-Dabieshan orogenic beltrdquo InternationalGeology Review vol 57 no 3 pp 327ndash341 2015

[54] Y Wu C Zhang J Mao H Ouyang and J Sun ldquoThe geneticrelationship between hydrocarbon systems and MississippiValley-type Zn-Pb deposits along the SW margin of SichuanBasin Chinardquo International Geology Review vol 55 no 8 pp941ndash957 2013

[55] M Corbella C Ayora and E Cardellach ldquoHydrothermalmixing carbonate dissolution and sulfide precipitation in Mis-sissippi Valley-type depositsrdquoMineralium Deposita vol 39 no3 pp 344ndash357 2004

[56] D C Bradley and D L Leach ldquoTectonic controls of MississippiValley-type lead-zinc mineralization in orogenic forelandsrdquoMineralium Deposita vol 38 no 6 pp 652ndash667 2003

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in