Platform

European margin

( V = Volcanic Arc)Tauride-Anatolide

and Armenian block(s)

Metamorphic massifs

Sevan-Akera

suture zone

Strike slip faults

Thrust

Gedabek-Karadagh

ore district

25°E 45°E40°E35°E30°E 50°E

35°N

40°N

45°N

Caspian Sea

Black Sea

Arabian Platform

European Platform

Armenian Block(s)

Iranian

block(s)

1a

5 km

40°40’00’’

45°42’35’’

45°42’35’’ 45°53’20’’

45°53’20’’

40°40’00’’

Kharkhar

Kharadagh

Djaygir

Gedabek

Bitti-Bulakh

Maarif

1b

165

162

161

128

124

119

121

123

??

174

170

162128

119

123

124

162123 Py

Py Cp

Sp

Sp

Sp Sp

Sp

2a

Pyrite

Sphalerite

Chalcopyrite

Arsenopyrite

Tennantite

Pyrite spheroidal

Pyrite euhedral

Pyrrhotite

Sericite

Adularia

Quartz

Rutile

Malachite

Azurite

Enargite/Luzonite

Covellite

Chalcocite

Magnetite

Electrum

Hessite

Galena

Mottramite

Barite

Calcite

Stage 3Stage 2Stage 1Disseminated

mineralization

Semi-massive mineralization

or vein/veinletDisseminated

mineralizationCopper Enrichment Veins Oxydation Zone

Stage 4 Stage 5

Silicification non mineralized

Argillic Alteration

Oxydation Zone

Disseminated Pyrite (1st st.)

Semi-massive pyrite (2nd st.)

Semi-massive mineralization (2nd st.)

Veinlets (2nd st.)

Disseminated mineralization (2nd st.)

0.1

1

10

100

1000

0.01 0.1 1 10 100

Au (ppm)

Ag

(p

pm

)

4a

1

10

100

1000

10000

100000

1000000

0.01 0.1 1 10 100

Au (ppm)

Cu

(p

pm

)

4b

1

10

100

1000

10000

100000

1000000

0.1 1 10 100 1000

Ag (ppm)

Cu

(p

pm

)

4c

0.01

0.1

1

10

100

1000

0.01 0.1 1 10 100

Au (ppm)B

i &

Te (

pp

m)

Bi

Te

4e

1

10

100

1000

10000

100000

0.01 0.1 1 10 100

Au (ppm)

Pb

(p

pm

)

4f

0

2

4

6

8

10

12

14

16

18

20

80 85 90 95 100

mol% ZnS in sphalerite

mo

l% F

eS

in

sp

ha

leri

te

Inclusion in massive pyrite

Massive mineralization

Vein mineralization

Disseminated mineralization

Veinlets mineralization

Inclusion in disseminated pyrite

5gEquilibrium with pyrite

Uncertain equilibrium with pyrite

3e

400μm

gn

tn

cp

py

asp

mt

quartz

adularia

0.2 mm

sptn

3d

cp

asp

100μm

cv

cpenr

3f

rt

2 cm

cp

sp

quartz adularia3b

20μm

galena

tennantite

hessite

AgAu3

cp

asp tennantite

microcrystalline

quartz-adularia

4d

5mm

sp

cp

Disseminated

py

cv

3a

5mm

py

adularia

qtz

3c

100 μm

py

cp

5c

200 μm

py

cp5d

0.3 mm

cp sp

cv

5e

5b

100 μm

cppy

mr

400μm

5fsp

bar

cc

300μm

5a

cp

sp

asp

po

py

2b

2c

2d

2e

Andesitic volcanoclastic rocks (Bajocian)

Granodiorite (Kimmeridgian - 133-142 Ma)

Non mineralized silici#ed body

Mineralized silici#ed body

Oxydation Zones

Fractured Unit - Undetermined

Breccia - Uncharacterized type

Argillic alteration

Quaternary

Disseminated Pyrite (approximative density)

Semi-massive mineralization

Carbonate veins

Dykes

Faults

Fault

Quaternary, alluvial

Bajocian subvolcanic dacite,

rhyodacite, ryholite

Bathonian subvolcanic diabase,partly porphyritic

Bajocian plagiogranite, tonalite

(K-Ar age: 152-162 Ma + 172 Ma)

Kimmeridgian granodiorite

and quartz-diorite(K-Ar age: 133-142 Ma + 150 Ma)

Kimmeridgian quartz-diorite

and diorite, partly porphyryitic

Lower Bajocian porphyritic andesite,

tu! and tu! brecciaBathonian andesitic volcanic

and pyroclastic rocksCallovian-Oxfordian

pyroclastic rocks

Upper Bajocian rhyolite, porphyritic

rhyodacite, rhyodacitic tu! and tu! breccia

200 m

3g

The Gedabek epithermal Cu-Au deposit, Lesser Caucasus, Western Azerbaijan:

Geology, alterations, petrography and evolution of the sulfidation fluid states.

Pierre Hemon1, Robert Moritz1, Vagif Ramazanov2

3- Paragenetic Sequence:

Three main mineralization stages:

First Stage: Disseminated pyrite (+/-rutile), pervasive through the whole deposit, together with microcrystalline

quartz-adularia +/- sericite and barite. Fig.3a shows a clear crosscut by the second stage.

Second Stage: shows different styles of mineralization: semi-massive sulfide lenses (fig.3b&c), veins, veinlets (fig.3a)

and disseminated mineralization (fig.3e). Differences of mineralogy are observed depending if the mineralization is

rather �massive� or rather disseminated. Massive mineralization occurs with chalcopyrite, sphalerite and/or pyrite domi-

nant, plus minor arsenopyrite, tennantite and pyrrhotite (fig.3d). Disseminated mineralization (fig.3e) is associated with

dominant galena, chalcopyrite and tennantite. Although no clear relationship are observable to clearly differentiate differ-

ent stages from these different styles.

Third Stage (fig.3f): hypogene enrichment in copper by mineralization of chalcocite, covelite, and few occurrences of

enargite (or luzonite).

Two main supergene stages:

Fourth Stage: Calcite veining cross-cutting argillic alteration, less than 1cm wide. This stage indicates neutralization

of the system, and oxygen isotopes indicate a meteoric origin of these veins.

Fifth Stage: Copper and vanadium oxides (azurite, malachite and mottramite) forming the oxidation zone.

4 - Ore Mineralization:

No visible gold has been reported at the Gedabek deposit, but analyses of metal content on mineralized samples allow some

interpretations (fig.4a,b&c):

The disseminated pyrite (1st stage) or massive pyrite (2nd stage) are associated with really low grades of ore mineralization

(<1ppm Au).

Massive mineralization of chalcopyrite and sphalerite (2nd stage), as well as the disseminated mineralization (2nd stage)

are associated with the best ore grades. Samples from the argillic alteration show really low contents of metals.

Really rare tiny grains of electrum are microscopically observable (fig.4d). Approximate measurements made on electrum

grains with an SEM indicate a Au/Ag ratio of 3. Microscopic electrum grains were observable within the disseminated min-

eralization of the second stage (cf.fig.3e). Optically, electrum is associated with galena, tennantite, hessite and chalcopyrite

(fig.4d).

Metal content analyses of whole rock analyses indicate a really high correlation between Au content and Bi, Te, Pb and Ag

(respectively 0.98, 0.91, 0.89 and 0.87; fig.4a,e&f), which can be interpreted as a strong association of gold with silver

(electrum), galena and hessite.

5 - Sulfidation Fluid State Evolution

First Stage: Disseminated pyrite, no data.

Second Stage: Large chalcopyrite crystals from the massive mineralization show various patterns of an increase in the sulfidation state

of the system:

Pyrrhotite inclusions (fig.5a) show different stages of replacement toward marcassite with squelletic texture (fig.5b) and then pyrite with

a spongy texture. According to Ramdohr (1969), this replacement of pyrrhotite by pyrite (FeS + S = FeS2) might be due to an increase of

the S content of the system.

Pyrite spheroids (fig.5c) and euhedral pyrites (fig.5d) observed in large crystals of chalcopyrite indicate an excess of Fe during crystalliza-

tion of chalcopyrite. This is also supported by the occurrence of thin lamellae / exsolution of pyrrhotite within chalcopyrite. According to

Bonev (1974), pyrite spheroids and euhedral pyrites are formed through a reconstructive reaction of Fe-rich chalcopyrite: CuFeS2 = Cu

+ FeS2. Even if there is no addition of sulfur in this reaction, Bonev (1974) concluded that this reaction might take place under condition

of high sulfur potential at low temperature.

Third Stage: Common preferential replacement of sphalerite rather than chalcopyrite by covellite (fig.5e) is indicative of an increase of

the sulfidation state of the system.

Observation of some enargite rims around chalcocite or covellite indicates a sulfidation state of the fluids significantly higher relative to

pyrrhotite from the second stage.

Microprobe analyses made on sphalerites, from the 2nd stage, in equilibrium with pyrite, show a large range of FeS content (fig.5g).

Based on petrological observation (e.g. fig.5f), FeS content in sphalerite evolves from higher values (18 FeSmol%) toward lower values

(2 FeSmol%).

Conclusion:

According to the classification by Simmons et al.(2005), based on gangue mineral assemblages, mineralization in the Gedabek ore deposit is associated with a Quartz-Adularia-Illite+/-Calcite assem-

blage. At Gedabek, the shape of the silicified body is mostly controlled by the permeability of the volcanoclastic rocks leading to this first disseminated mineralization stage.

Alterations indicate an evolution of the fluids from silicification to argillic alteration. According to a previous report, fluid acidity also led to the local formation of vuggy silica.

Microprobe analyses on the FeS content of sphalerite from the second stage indicate that mineralization is associated with an intermediate sulfidation state of the fluids (Einaudi et al.,2003; Sillitoe

and Hedenquist, 2003), including a large range of values from the lower to the higher limit. Petrographic observations are also consistent with a general increase of the sulfidation state of the system,

and the third stage of mineralization seems to indicate a further evolution of these fluids, leading to the formation of abundant covellite and some enargite.

Fig.1b: Geological Map of Gedabek-Karadagh ore district, drawn by Robert Moritz.

Fig.2a: Geological map of the Gedabek ore deposit, modi!ed after Anglo Asian Mining PLC (2011).

Ressource estimate by SRK (January 2007), with a 0.3g/t Au cut-o".

Fig.2b: Propylitic alteration along preferential layer of py-

roclastic andesitic rocks.

Fig.2c: Silici!cation along preferential layers of tu", at

contact between silici!ed ore body and tu"s.

Fig.2d: Silici!ed orebody: rhyolitic texture overprinting the

still visible clasts from tu".

Fig.2e: Argillic alteration crosscutting the silici!ed body

and crosscut by calcite veins.

Fig.3: a) Disseminated pyrite from the !rst stage, cross-cut by a veinlet from the second stage. b) Semi-massive mineralization from the second stage,

chalcopyrite-sphalerite dominant with quartz-adularia gangue. c) Semi-massive mineralization from the second stage, pyrite dominant. d) Common

texture with arsenopyrite-tennantite-sphalerite in large chalcopyrite crystals from the second stage. e) Disseminated mineralization from the second

stage, galena, tennantite dominant. f ) Third stage mineralization, covellite and enargite replacing chalcopyrite. g) Paragenetic sequence from the Geda-

bek ore deposit; Thick bars: dominant minerals; Thin bars: Minor mineralization; Doted bars: Uncertain.

Fig.5: a) Pyrrhotite residue within a large chalcopyrite crystal. b) Pyrrhotite replacement by Marcassite and Pyrite within a large chalcopy-

rite. c) Pyrite spheroids within large chalcopyrite. d) Euhedral pyrites. e) Preferential replacement of sphalerite by covellite. f ) Direction of

the pro!l made on sphalerite crystal from chalcopyrite free veinlets (cf !g.5g). g) Microprobe analyses on di"erent sphalerites from the

second stage. Arrow refers to the !g.5f.

Fig.4: a) Plot of Ag vs. Au content from whole rock analyses on Gedabek samples. b) Cu vs. Au. c) Cu vs. Ag. d) Backscatter imaging of electrum grain and

associated minerals. e) Bi and Te vs. Au. f ) Pb vs. Au.

Fig.1a Tectonic Map of the Caucasus, after Rolland et al. (2010), modi!ed.

2 - Gedabek Ore Deposit:

This study focuses on the Gedabek epithermal deposit which is the only one from this district currently exploited by the

Anglo Asian Mining PLC (cf. ressource estimate fig.2a).

Geology of the Gedabek ore deposit (fig.2b) consists of andesitic volcanoclastic rocks (Bajocian) intruded by a granodior-

ite massif (Late Upper Jurassic). Ore mineralization is associated with a flat silicified body, laying at the contact between

the tuffs and the granodiorite.

Mineralization consits of disseminated pyrite together with a pervasive silicification. Semi-massive mineralization, lense

shaped, with dominant sphalerite-chalcopyrite, occurs in the central part of the orebody, associated with the best ore grades

of the deposit.

Primary rock permeability strongly controls the two main pervasive alterations (fig. 2b & c).

Propylitic alteration (fig.2b): epidote, chlorite and magnetite. In tuffs surrounding the ore body.

Quartz-sericite-pyrite (fig.2c&d): this alteration is associated with the ore mineralization. It is characterized by mi-

crocrystalline quartz together with quartz phenocrysts (rhyolitic texture), sometimes the primary texture is still distinguish-

able (tuff clasts). Thin section observations indicate an evolution of this alteration from pure quartz (and adularia??),

toward quartz-sericite, and then quartz-sericite-pyrite.

Argillic alteration (fig.2e): post mineralization, (dickite, chlorite, quartz, +/- kaolinite), crosscut by carbonate veins of

meteoric origin (oxygen isotopes)

Vuggy Silica has been reported in a previous study on the deposit (SGS, 2010).

The Gedabek ore deposit has previously been classified either as a Au porphyry deposit (SRK, 2007), or as a high-

sulfidation epithermal deposit (SGS, 2010).

1 - Introduction:

The Gedabek-Karadagh ore district is emplaced in the Lesser Caucasus, north of the Sevan-Akera suture zone (Fig,1a).

The Lesser Caucasus is the result of the still going collision between the European and Arabian platform. It is classically di-

vided into three main parts (Sosson et al., 2010), from south to north: 1) The south Armenian block, a Gondwana derived

block, representing carbonate platform; 2) The Seven-Akera suture zone, an ophiolite belt which represents the closure of

the Tethys ocean; 3) The Eurasian margin, which represents volcanic arc formation.

The major magmatic activity of the volcanic arc is estimated at Middle Jurassic, many ore deposits in the area are linked to

this magmatic event.

The geology of the Gedabek-Karadagh ore district (fig.1b) consists of tuff, from andesitic to rhyolitic composition, intruded

by two magmatic events: 1) plagiogranite intrusion dated as Upper Bajossian (~162My); 2) gabbro-diorite to quartz diorite

massifs, dated as Late Upper Jurassic (~138My) (Ismet et al., 2003).

The Gedabek-Karadagh ore district is the biggest porphyry district of Azerbaijan, Karadagh, Xarxar and Djagir deposits are

characteristic of Cu-Au porphyry deposits. Bitibulak is characteristic of a high sulfidation deposit. The aim of this study is

to characterize the Gedabek deposit.

1: University of Geneva, Department of Mineralogy, Rue des maraîchers 13, CH-1205 Geneva

2: University of Baku, Baku, Azerbaijan

References:Bonev, (1974), Fourth IAGOD Symposium, Varna, Vol.II.

Einaudi et al., (2003), SEG Spec. Publ. Vol.10.

Ismet et al., (2003), Baku “Nafta-Press”.

SGS Canada (2010), AAM PLC !les.

Sillitoe and Hedenquist (2003), SEG Spec. Publ. Vol.10.

Simmons et al., (2005), Econ. Geol. 100th Anniversary Vol.

Sosson et al., (2010), Geol. Soc. London, Spec. Publ., Vol.340.

SRK consulting (2007), AIMC !les.

Ramdhor (1969), 3rd Edition, Pergamon Press.

Rolland et al., (2010), Geol. Soc. London, Spec. Publ., Vol.340.

Thank you to the geologist team from AAM-PLC, Kalin Kouzmanov, Marie Caroline Pinget, Jorge Spangenberg and

Benita Putlitz for their great help in this project .