minerogenetic mechanism of the songxi silver-antimony deposit of northeastern...

Vol. 18 No. 3 CHINESE JOURNAL OF GEOCHEMISTRY 1999

Minerogenetic Mechanism of the Songxi Silver- Antimony Deposit of Northeastern Guangdong

Ore-Controlling Role of Organic Matter

H U KAI (i~j N ) 1), XIAO ZHENYU ( ~ _ ~ ) 2 ) , ZHAI J IANPING ( ~ ) 1 ) , Y U CHENSHENG ( = j z j ~ ) l ) , HUANG ZHEN ( ~ ~ ) 2 ) , AND L I U Q I N G (~'lJ j :~) l)

1) ( State Key Laboratory of Mineral Deposit Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China)

2) (Guangdong Nonferrous Metals Geological Exploration Bureau, Guangzhou 510080, China )

Abstract: Organic geochemistry and comparisons of characteristics of the organic matter in wall rocks of the ore-controlling strata and ores of the Lower Jurassic Songling black shale formation and the related Songxi silver-antimony deposit of northeastern Guangdong have been studied in this paper. The results show that the Lower Jurassic Songling shale formation is a suite of biologic-rich and organic-rich ore-bearing marine sedimentary rocks. Micro-components of the organic matter in the Songling black shale formation consists primarily of algae, amorphous marine kerogen, solid bitumen, and pyrobitumen. The thermal evolution of organic matter is at the over-maturity stage. There is a general positive correlation between total organic carbon (TOC) and metallogenetic elements such as Ag and Sb in the black shale formation. Organic matter in the host rocks in the Songxi ore deposit played a role in controlling the silver-antimony depositing environment during the forming process of the black shale ore-bearing formation. In the absence of vitrinite, the relative level of thermal maturity calculated by solid bitumen reflectance indicates that the ore-forming temperature of the Songxi silver-antimony deposit was about 150 - 170"(2, which was considered as an epithermally reworked ore deposit. The roles of organic matter in the formation of the Songxi ore deposit are a primitive accumulation of the metallogenetic elements (A4~, Sb) in the sea-water cycle system for ore source and a concentration of metals by ion exchange or chelation as well as reduction of the oxidized metals.

Key words: Songxi silver-antimony deposit; organic matter; total organic carbon (TOE); metallogenetic association

The Songxi silver-antimony deposit was found to be an independent large-sized deposit with a silver-antimony assemblage in recent years in our country, which occurs in a suite of Lower Juras- sic Songling ore-bearing black shale formations in northeastern Guangdong, South China. Low- metamorphic degree, biologic-enrichment and organic-enrichment of the host rocks are the major geological characters of this suite of Songling black shale ore-bearing formations. In this paper, we discussed and compared the characteristics of organic matter in the host rocks and metallogenetic association with the organic matter in both mineralized and unmineralized samples using the organic geochemical method. It was hoped that this would contribute to a better understanding of the origin of the ore deposit on the basis of newly developed organic geochemical techniques.

ISSN 1000-9426 * This project was jointly supported by the National Natural Science Foundation of China (No: 49872037), the Doctoral Program Foundation for Key Subjects from the Ministry of Education of China (No: 96028430), and the State Key Laboratory of Mineral Deposit Research, Nanjing University.

306 CHINESE JOURNAL OF GEOCHEMISTRY Vol. 18

Geological Setting of the Ore Deposit

The Songxi silver-antimony deposit lies at the south margin of the Yongdin-Meixian Palaeo- zoic folded zone and the north margin of the Zhaigong Mesozoic volcano-sedimentary basin of the Caledonedes, South China. The main structure line of this region is NW-striking and consists of a series of folded and faulted structures. The strata exposed in the mining area are only the Lower Jurassic Songling Formation and Middle Jurassic Zhangping Formation. Orebody of the Songxi silver-antimony deposit occurs mainly within the Lower Jurassic Songling Formation. The Songling Formation strata consist of the upper, middle and lower lithologic members, but the latter two can be seen only in the ore district. Host rocks of the middle lithologic member of the Songling Formation mainly comprise greyish white-greyish yellow silicarenite, fine-grained sand- stone and siltstone, and their grain size gradually reduces from the bottom to the top. The upper portion of the upper lithologic member is intercalated with black shale, sedimentary tuff, and stratiform silver-antimony orebody. The lower portion of the upper lithologic member consists mainly of black shale, silicarenite, siltstone, biologic fragmental limestone, sedimentary tuff and basalt, which is the most important ore-bearing bed.

The Songling silver-antimony ore deposit occurs on the two limbs of an open anticlinal structure at the turning point, especially on the northeastern limb. This anticlinal structure axis is NW-SE striking and dips in the SE direction. Strata on the two limbs of the anticlinal structure incline at an angle of about 40* - 60 °, which consist of the Lower Jurassic Songling Formation and Middle Jurassic Zhangping Formation. The surroundings of the ore district are unconformably covered by Upper Jurassic continental volcanic rocks. Based on observations in the field and drill- core data, the orebody may be divided into three types, i . e . , bedded ore, lens-shaped ore and vein ore. The vein orebody intersects the Songling Formation strata and forms a comb ore structure due to quartz vertically filling vein walls (Xiao Zhenyu, 1997; Zheng Qiannian, 1996).

Samples and Analytical Methods

Samples

A total of 57 samples were collected from the mining district, and 12 mineralized samples were collected from working faces of carbonaceous ore of the No. 4 orebody and waste in its open pit. Other 45 unmineralized samples were separately collected from drill holes ZK609 and ZK1011 located in an unaltered area far from the mining district.

Each of the samples was generally required to be separated into two portions. One portion was polished as a polished section or a thin section for optically microscopic observation of carbonaceous materials in the rocks. The other portion was crushed as fine as approximately 100 mesh for the analysis of total organic carbon, silver, antimony and soluble organic matter extract.

Analytical methods

A Leco CS 224 Carbon-sulfur analyser was used for whole-rock organic carbon analysis. Be- fore organic carbon content was determined, unextracted rocks were treated with hot 6N HC1 to remove carbonate. Silver and antimony contents were separately determined by atomic absorption spectrophotometry (precision 0.1 × 10-9) or X-ray fluorescence spectrometry (precision, 0.1 × 10-6), depending on their respective contents. Bitumen reflectance measurement was performed

No. 3 CHINESE JOURNAL OF GEOCHEMISTRY 307

on whole rock, using Opton Universal reflecting microscope under oil immersion at a magnifica- tion of 250 × . If possible, at least 10 measurements were made on each sample. Gas chromatographic analyses were performed on a Hewle t t -Packward 5890 chromatograph ( II ) . Helium was used as a carrier gas with a flow rate of 1 m l /min . The GC temperature was increased at a rate of 6 " C / m i n to 290"C.

Results and Discuss ion

Micro-components o f the organic matter and their modes of occurrence

Micro-components of the organic matter and their modes of occurrence in unmineralized and mineralized rocks of the Songling shale formation of the Songxi si lver-antimony deposit were syn- thetically described in Table 1. As can be seen from Table 1, micro-components of the organic matter in the host rocks of the Songling shale formation consist primarily of alginite, amorphous marine kerogen, solid bitumen, and pyrobitumen.

Sample locality

Table 1. Modes of occurrence and micro-components of organic matter in wall rocks and ore-bearing rocks of the Songxi silver-antimony deposit

Organic Reflectance of Micro-organic Stratigraphic Lithology Mode of occurrence unit carbon ( % ) bitumen ( % ) component

Drill holes ZK609 and ZK1011 (wall rock)

Carbonaceous Uniform distribution or shale, silt- with laminated-fine dis- Lower Juras-

sic Songling stone, Alga, solid persed organic matter in Formation argiUite, 0.03 - 4.20 0.95 - 5.46 bitumen, primary bedding surface a- (J1,) limestone, kerogen long rock stratification,

sedimentary- forming a black laminated tuff, basalt and mesh structure

- 13m level (ore zone)

Particle distribution; not Carbonaceous Solid bitu- uniformly or distributed a-

Lower Juras- shale, silt- long rock cracks to form men, pyrobi- stringer veins, often sic Songling stone, 0.09- 5.00 1.19- 4.42 tumen, amor-

Formation argillite, sedi- coenosarc with metal min- ( J l s ) mentary-tuff, phous erals, such as pyrite,

basalt graphite allcharite, chalcopyrite, galena, etc.

Microscopic petrographic observations of both polished and thin sections of the host rocks under the reflected light and t ransmit ted light indicated that there are two types of organic micro- components in the host rocks in accordance with their modes of occurrence. The first type of organic mat te r was distributed in black shale and siltstone with laminated-fine dispersed organic matter , the aggregates of which generally occur in pr imary bedding surface along rock stratification, forming a black laminated and mesh structure under the transmitted light. Organic mat ter of this type has well preserved the features of pr imary bioclastic texture (algnite, marine amorphous kerogen) and has also reflected the pr imary sediment environmental character of the Songling black shale formation. T he second type of organic mat ter was composed mainly of some solid bi tumen and pyrobi tumen, some of which were often coenosarc with metal minerals, such as stibnite, pyrite, chalcopyrite and galena. Because of the effect of hydrothermal reworking and tectonism, this type of organic mat ter has evolved into amorphous graphite and pyrobitumen. Some of the pyrobi tumen infiltrated along rock cracks to form stringer veins. Microscopic petrographic observation of organic mat ter in both unmineralized and mineralized samples shows that


the amorphous graphite and pyrobitumen mostly exist within ore zones, which are closely associated with silver-antimony mineralization.

Contents of total organic carbon, silver and antimony and their correlations

Table 2 lists the contents of total organic carbon (TOC) , silver and antimony of 57 samples from the wall rocks and mineralized rocks (near the No. 4 ore vein) of the Songxi ore deposit. As shown in Table 2, the analytical results show some significant characteristics: (1) There is a significant difference in TOC content for different rocks, with the lowest TOC content in the rocks being only 0 .03% and the highest in carbonaceous shales being up to 5 . 0 % . (2) The TOC content of the carbonaceous shale is highest with the average value of 21 samples being 1.02 %. The TOC concentrations of the various rocks tend to decrease in the order of carbonaceous shale ( 1 .02 % )--~siltstone (0 .14 % )--~argillite (0 .14 % )--~sediment-tuff (0 .08 % )--~basalt (0 .04 % ). (3) There is a greater difference in TOC content of the 12 mineralized samples collected from working face of the No. 4 ore vein under about 200m level of the open pit, ranging from 0 .09 % up to 5 .0 %, averaging 1 .09 %. The TOC average of the mineralized samples is higher than that of various wall-rock samples. The analytical results of the TOC content of the host rocks further indicate that the Lower Jurassic Songling black shale formation is a suite of organic-rich and biologic-rich sedimentary rocks. (4) The silver content of the wall rocks lies mainly between 0 .02 × 10-6 and 5 .94 × 10-6, averaging between 0~.26 × 10-6 and 1.06 × 10-6, depending on different lithologic rocks. Our results show that the silver content of the host rocks of the Songling shale formation is generally several to tens of times higher than that of the same lithologic rocks in the upper continental crust (Liu Yingjun et a l . , 1984). The silver content of ore from the Songxi ore deposit may be as high as up to 1050 × 10 -6 . (5) The antimony content of the wall rocks mainly varies between 11.13 × 10 -6 and 733.5 × 10 -6, averaging 29 .02 × 10 -6 to 133.4 × 10 -6, depending on different lithological characters, which is also a ~few times to several tens of times higher than that of the same lithologic rocks in the upper continental crust (L iu Yingjun et al . , 1984).

Table 2. Contents of total organic carbon, silver, antimom Sample Stratigraphic No. of TOC( % ) locality unit samples

Carlxmaeeo~ shale 22 Drill holes Siltstone 10 ZK609 and ZK1011 Argillite 9 (host rock) Sedimentary-tuff 2

Basalt 3 - 13m level Ore-bearing 12 (ore zone) carbonaceous shale

Range Average 0.09-4.20 1.02 0.04-0.33 0.14 0.03 - 0.44 0.14 0.03-0.12 0.08 0.03-0.05 0.04

0.09-5.00 1.09

in various host rocks of the Songxi deposit Ag( × I0 -6) Sb( x 10 -6)

Range Average Range Average 40.38 30.29 133.4 29.09 63.73

0.97- 1050 99.28 76.0- 359000 44686

0.04 - 1.88 0.75 o. 04 - 2.86 o. 44 o. 02 - 5.94 1.06 0.36-1.63 1.00 o. 05 - o. 65 o. 26

17.25 - 70.0 11.31 - 74.75 11.81-733.3 23.93 - 34.25

39.69 - 94

Good correlations are observed between total organic carbon (TOC) and silver, and antimony of 27 samples in various rocks from drill hole ZK609 and the results are shown in Fig. l ( a , b ) . It is interesting to note from Fig. l ( a , b) that there is a general positive correlation between total organic carbon(TOC) and silver (Fig. l a ) , and antimony (Fig. l b ) . The TOC-Ag and TOC-Sb relationships indicate that organic-rich black clay layers in the Songling Formation are often char- acterized by the enrichment of silver-antimony metallogenetic elements. Obviously, the organic mat ter in the host rocks may play a controlling role in silver-antimony depositing environment during the formation of the black shale ore-bearing formation.


t 6 . 0

14 .0

12 .0

~ " lO+0 ' o x 8 . 0

6 . 0

4 . 0

2 . 0 O

0 . 0 0 . 0 0

Drill hole ZK609 N=27

o

• •

r i i

0 . 5 0 1 .00 1 .50 2 . 0 0 2 , 5 0

250. 0

200. 0

1 5 0 . 0

× 100. 0

5 0 . 0 (a)

0 . 0 3 . ~ 0 . ~ 3 . ~

Drill hole ZK609 N=27

. •

tO 411 •

to (b) ~o • •

n i k n t

0 . 5 0 l . O0 1 .50 2 . 0 0 2 .50

T O C ( % ) T O C ( % )

Fig. 1. Relationships between TOC and silver, antimony in the host rocks of the Songling Formation.

Gas chromatographic characteristics of the saturated hydrocarbons

In order to compare soluble organic matter in unmineralized sample with that in mineralized sample, we selected one unmineralized sample (sample ZK1011-125, wall rock) and one mineralized sample (sample SXV4-6, near orebody) for gas chromatographic analysis of their saturated hydrocarbons. The analytical results are shown in Fig. 2. It can be seen from Fig. 2, there are some differences in the gas chromatographic character of the saturated hydrocarbon fractions between the unmineralized sample and the mineralized sample: (1) Some normal C15 to C22 hydrocarbons have been detected in the extracts of the two samples, such as normal alkanes, isoprenoid alkanes, pristane and phytane. Carbon number distribution of n-alkanes in the two samples is rel- atively narrow, only at nCt5 to nC23, with a maximum peak of n-alkanes at nC18 to nC20. This distribution pattern is characteristic of marine organic matter of microbial or algal origin deposited under extremely reducing conditions (Tissot and Welte, 1978). (2) Gas chromatograms of the saturated hydrocarbons in the unmineralized sample show a smooth distribution pattern of n-alkanes and a smooth naphthene peak (nC19), in contrast to the irregular distribution of the mineralized sample and two naphthene peaks (nCts, nC20, ). Gas chromatograms of the saturated hydrocarbons of the mineralized sample indicate that organic matter in the mineralized sample has undergone strong catagenesis (or mineralization) since few hydrocarbons have been recorded above nC20(Macqueen and Powell, 1983). (3) Gas chromatograms of the saturated hydrocarbons from wall-rock sample ZK1011-125 show no particular predominance of pristance and phytance over n- alkanes, with a pristance/phytance ratio above 1, while sample SXV4-6 has a higher concentration relative to the adjacent n-alkances, with a pristane/phytance ratio being approximately 1. The former was deposited in a less strongly reducing condition, while the latter was deposited under extremely reducing conditions (Macqueen and Powell, 1983). On one hand, this study shows that the gas chromatographic characteristics of the saturated hydrocarbon fractions in the unmineralized and mineralized samples demonstrate the organic matter is of microbial or algal origin. On the other hand, it also suggests that the organic mater within the ore zone has undergone exten- sive catagenesis or epithermally reworked mineralization, leading to the absence of some normal isoprenoid alkanes (Fig. 2).


\

1 31011-1215 c($ ti9 CI8 (20 C19 +j ¢17

Cl" c16 "'-x....

Fig. 2. Gas chromatograms of the saturated hydrocarbons in unmineralized and mineralized samples of the Songxi deposit.

Thermal maturation o f organic matter and temperature of silver-antimony mineralization

The thermal maturity (or degree of maturation) of organic matter is a major parameter for thermal evolution process, which will influence the composition of organic matter and its potential role in the formation of the Songxi silver-antimony ore deposit. The extent of maturation of organic matter is a function of both time and temperature (Connan, 1974). Simply, three stages of progressive maturation of organic matter can be distinguished. The first stage, below approximately 9012, is referred to, in organic geochemistry, as diagenesis. The second stage is followed at about 9 0 - 12012 by the main stage of petroleum generation (van Krevelen, 1984). The last stage of thermal alteration is metagenesis , during which organic matter is transformed into graphite. Therefore, the thermal maturity of organic matter is usually considered as an important parameter of geological thermal event or used to estimate the paleo-geotemperature of metal mineralization (Hu Kai, 1993; Li Zhaolin, 1997).

As we know, vitrinite reflectance is the most direct parameter to evaluate the thermal maturity of organic matter. Solid bitumen reflectance of samples from 13 ore districts are presented in Table 3. In the case of no vitrinite, the abundance and regional distribution of solid bitumen in host rocks of the Songling black shale formation made them an ideal candidate for reflectance study. Xiao Xianming et al. (1991) have established correlations between vitrinite reflectance and the reflectance of solid bitumen in coals and carbonates. For convenience, we used Xiao Xian- ming ' s method (1991) to calculate vitrinite reflectance (R °) in terms of solid bitumen reflectance (R°) . The vitrinite reflectance data calculated from solid bitumen reflectance are also presented in Table 3. As shown in Table 3, vitrinite reflectance values are in the range 1.75 % < R°< 3 .02 %, mostly above 2 .0 %. Reflectance results show that organic matter from the ore districts has undergone thermal evolution at the stage of over maturation. It is important to note that vitrinite reflectance of the mineralized sample shows a slight increase as comparied with that of the unmineralized sample, with an average vitrinite reflectance increase in the range about 0 .10% < R ° < 0 . 5 0 % . In other words, the silver-antimony mineralization of the deposit further intensified the thermal evolution of organic matter so that an additional organic thermal anomalous value ap- peared within the ore district (Table 3) .

Paleo-geotemperatures were estimated based on the vitrinite reflectance data following the procedures of Hood D. et al. (1975). In consideration of the crust evolution and lithofacies paleo- geography the time over which the strata in the basin were effectively heated was taken to be 180 Ma. The paleo-geotemperatures thus calculated on H o o d ' s temperature-time diagram are


1 5 0 - 170"12 (average 157"(2 ) for the Songxi ore deposit. This temperature range is in approxi- mate agreement with the actual formation temperature range of 160 - 230*(2 at the major stage of mineralization as measured by quartz fluid inclusion homogenization temperatures (Yao Dexian et a l . , 1996) . It can be inferred that the ore-forming temperature of the Songxi silver-antimony deposit was about 1 5 0 - 170"(2. So the deposit is considered as an epithermally reworked ore deposit.

Role o f organic matter in silver-antimony mineralization

The role of organic mat ter in ore deposition is complex and organic mat ter can play a special role in the field of ore deposits geochemistry. The organic carbon cycle in ore deposits should be given a particular emphasis in order to understand the origin of organic matter . Organic mat ter may play one or several important roles in the formation of ore deposits: adsorption, leaching, transport , concentration, reduction and precipitation of ore metals. Our s tudy demonstrates tha t organic mat ter played the following important roles in the formation of the Songxi ore deposit during Ag-Sb mineralization.

Table 3. Organic matter reflectance of the host rocks and paleo-temperatures of the Songxi deposit Sample locality Number of deter- R°~x R,0~ ~0 ~0~ Mineralization Paleotempera-

Drillhole Depth(m) Sample number Lithology mined points (%) (%) (%) (%) character ture~('C)

ZK609

10 ZK609-10 Siltstone 24 3.88 2.75 3.14 2.44 Unmineralized 158 246 ZK609-246 Carbonaceous shale 20 2.93 1.40 2.10 1.75 Unmineralized 140 277 ZK609-277 Carbonaeeous shale 26 5.46 3.30 4.28 3.20 Pyritization 170 301 ZK609-301 Carbonaceous shale 20 4.74 3.04 3.87 2.93 Pyritization 165 336 ZK609-336 Carbonaceous shale 27 4.60 2.07 3.70 2.82 Pyritization 160

ZK1011

90 ZKI011-90 Carbonaeeous shale 25 4.39 2.70 3.40 2.62 Stibnitization 155 101 ZK1011-101 Carbonaeeous shale 23 4.78 2.50 3.48 2.67 Stibnitization 155 120 ZK1011-120 Carbonaceous shale 11 3.12 0.95 2.47 2.00 Unmineralized 150 125 ZK1011-125 ~ l i m e s t o n e 4 4.31 2.81 3.35 2.58 Pyritization 155 217 ZK1011-217 Argillite 1 / / 4.09 3.08 Unmineralized 165 236 ZK1011-236 Limestone 31 3.78 2.32 3.02 2.36 Unmineralized 152

No. 4 vein - 13ra level SXV4-5 Carbonaceous shale 22 4.42 1.19 3.55 2.72 Stibnitization 160 -13mlevel SXV4-6 Carbonaeeousshale 24 4.39 3.03 3.78 2.87 Stibnitization 160

Note: @ K'° calculated by the equation: K'°=0.668 K'°+0.346, ~ Hood (1975),

Organic matter played a role in the primitive accumulation of metallogenetic elements (Ag , Sb) during the process of formation of the Songling black shales as ore source. The adsorption of organic mat ter may be a major way of enrichment of silver and ant imony in the sea-water cycle system. The above geological and geochemical observations have multiple implications for possible organic-Ag(Sb) interaction. Firstly, organic mat ter associated with the ores is predominantly of marine origin, such as algae and microbial and amorphous marine kerogens ( types I and l] ) . Secondly, the modes of occurrence of organic micro-components in the host rocks show that organic mat ter in the ore deposit is indigenous in nature rather than migrated f rom far. Thirdly, the relationship between T O C and silver, and ant imony (Fig . 1 ) fur ther proves that the enrichment of ore-forming metals and the formation of organic mat ter in the host rocks are concurrent.

Another role of organic mat ter is the concentration of metals by ion exchange or chelation and reduction of the oxidized metals. This role of organic mat ter in the Songxi ore deposit can be ex- pressed in the following chemical equations:

(a ) The concentration of silver and ant imony by ion exchange or chelation:


H H H r i [

4R- -CO -I + ( A g + , S b 3 + ) --~ R - - C - - O - A g + S b - ( O---CR )3 I I I

H H H

where R is an organic molecule; H, C and O are the organic elements hydrogen, carbon and oxy- gen.

(b) Indirect reduction of the oxidized metals through reduction of sulfate into sulfide by the oxidation of organic matter:

H I SO~4- + 2R- -C - OH--~H2S + 2RH + 2HCO3-

H HS- + 2Ag + ---~AgzS ~ + H +

3HS- + 2Sb3+---~SbzS3 ~, + 3H +

The above four equations are useful because they show the reactants and products of interac- tions of organic matter with metallogenetic elements. However, so far we have not given their ex- act mechanism or the rate of reaction. The alteration of organic matter and the coexistence of pyrobitumen with ores strongly support that organic matter is a critical factor leading to the concentration and reduction of ore metals in the sedimentary basin.

Conclusions

1. The Lower Jurassic Songling black shale formation of northeastern Guangdong is a suite of biologic-rich and organic-rich ore-bearing marine sedimentary rocks. The average total organic carbon (TOC) in the host rocks associated with silver-antimony mineralization is up to 1 . 0 9 %. The TOC content of carbonaceous shales is highest in the various lithologic rocks of the Songling shale formation, up to 5 .0 %.

2. The solid bitumen, amorphous marine kerogen and pyrobitumin are the main mirco-components of organic matter in the Songling shale formation. The vitrinite reflectance is, in most cases, above 2 .0 %, which indicates that the thermal evolution of organic matter lies at the stage of over maturity. The ore-forming temperature of the Songxi ore deposit, as deduced from vitrinite reflectance and temperature-time diagram (Hood, 1978), is 150 - 170"(2 (average 15712 ), showing that the Songxi ore deposit is an epithermally reworked deposit.

3. There is a positive correlation between total organic carbon (TOC) and silver, and antimony in the Songling black shale formation. This study shows that organic matter in the host rocks of the Songxi ore deposit played a controlling role in silver-antimony deposition during the forming process of the black shale ore-bearing formation.

4. The roles of organic matter in the formation of the Songxi ore deposit include the primitive accumulation of the metallogenetic elements (Ag, Sb) in the sea water cycle system for ore source and the concentration of metals by ion exchange or chelation as well as the reduction of oxidized metals.


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