Te and Se Mineralogy of The High-Sulfidation Kochbulak and Kairagach Epithermal Gold Telluride Deposits
Te and Se Mineralogy of The High-Sulfidation Kochbulak and Kairagach Epithermal Gold Telluride Deposits
Te and Se Mineralogy of The High-Sulfidation Kochbulak and Kairagach Epithermal Gold Telluride Deposits
DOI 10.1007/s00710-006-0130-z
Introduction
Most volcanic-hosted epithermal gold deposits (White and Hedenquist, 1990;
Bonham, 1986; Heald et al., 1987; Henley, 1991) are of Neogene or Paleogene
age. However, some of the largest deposits, including Kochbulak, Uzbekistan, are
Paleozoic in age. The Kochbulak and smaller Kairagach deposits are located
3.5 km apart near the town of Angren on the northern slope of the Kurama Ridge
188
in the Middle Tien Shan. The Kurama Ridge forms the eastern part of the extensive
Beltau-Kurama volcano-plutonic belt. Some modern geotectonic reconstructions
of this belt (Dalimov and Ganiev, 1994; Zonenshain et al., 1990) consider it to have
been an Andean-type continental margin volcanic belt that formed in the Late
Paleozoic on a Precambrian and Early Hercynian continental basement. This belt
is unusual in that it contains Paleozoic porphyry AuCuMo, AgPbZn skarn
and epithermal AuAgTeSe deposits (Fig. 1). The total gold resources of this
region exceed 2000 tonnes (Islamov et al., 1999), which makes this region a worldclass gold province. The estimated reserves of the Kochbulak deposit are 120 t of
Au and 400 t of Ag. Major ore components are Au (13.4 ppm) and Ag (120 ppm),
also Cu (0.2%), Se (4 ppm), Te (101.6 ppm) and Bi (0.01%). Reserves of the
Kairagach deposit are relatively small and are estimated to be 50 t of Au and
150 t of Ag. Gold is present mostly in native form but approximately 2025% of
the total gold reserves of these two deposits occur as various precious metal tellurides. Some researchers suggest that the Kochbulak and Kairagach deposits are part
of a single KochbulakKairagach ore field (Islamov et al., 1999).
Fig. 1. Schematic geological map of the central part of the Kurama Ridge (after
Kovalenker et al., 2003)
Te and Se mineralogy
189
Fig. 2. Schematic cross-section through the Karatash caldera along the line AB shown on
Fig. 1
190
(2) flat (2040 ) lenticular lodes, and (3) steeply dipping veins. At Kairagach, steeply dipping (7580 ) vein-like lodes and disseminated ore zones (sometimes flattening up to 10 at shallow levels) are typical. KAr and RbSr dating of sericite
yielded ages of 280 8 Ma and 270 8 Ma for pipe-like ore bodies and flat lodes
plus veins at Kochbulak, respectively, while an age of 280 5 Ma was obtained for
the lodes at Kairagach (Kovalenker et al., 2004).
Ore mineralogy
The ore-forming processes at Kochbulak and Kairagach can be subdivided into preore, ore, and post-ore stages. Mineralization of the pre-ore stage consists of vuggy
silica with pyrophyllite, diaspore, kaolinite, and alunite, as well as quartz-carbonate-sericite-pyrite rocks. The vuggy silica is present mostly at shallow levels of the
Kairagach deposit, whereas quartz-carbonate-sericite-pyrite rocks are widespread
throughout the Kochbulak and Kairagach ore fields.
Three ore stages were recognized in the Kochbulak deposit by Kovalenker et al.
(1980, 1997). Mineralization of the first stage consists of fine-grained to cryptocrystalline gray silica with variable amounts of pyrite, followed by quartz and
minor dolomite and barite with native gold, tellurides, and sulfosalts (Figs. 3a, 4a).
The second stage consists of banded silica, which in places occurs as a matrix
cementing clasts of quartz-pyrite aggregates of the first ore stage or altered porphyries (Fig. 3a), and contains native gold, bismuthinite, and tellurides. Hydrothermal mineralization of the third stage includes white quartz with pyrite,
goldfieldite, famatinite-luzonite, and minor Au and Ag tellurides (Fig. 4b), followed by fine-grained quartz with tetrahedrite, chalcopyrite, Sb- and Bi sulfosalts,
CuFe sulfostannates, tellurides, and sulfosalts of the lillianite series (Fig. 4c).
Fluid inclusion data (Kovalenker et al., 1997) showed homogenization temperatures from 100 to 400 C for the first ore stage, 100 to 300 C for the second ore
stage, and 100 to 320 C for the third ore stage. Fluid inclusions in quartz at the
beginning of each ore stage exhibited low to moderate salinity (0.56.5 wt.% equiv
NaCl) with NaCl and KCl being the dominant salts. Fluids responsible for the formation of quartz and barite spatially associated with tellurides and sulfosalts had
temperatures 250 to 130 C. The salinities of these fluids were 825 wt.% equiv
NaCl, with Fe2 , Mg2 and Ca2 , or Na and Ca2 being the dominant cations in
solution.
At the Kairagach deposit there are two ore stages. The first (early) ore stage
consists of gray metasomatic quartz with disseminated pyrite and minor chalcopyrite, and rare sphalerite, galena, and fahlores. Native gold is interspersed as
inclusions in quartz and pyrite (Fig. 3b).
The second (main) ore stage includes several assemblages that are closely related in time and are often telescoped spatially. The earliest assemblage consists of
segregations of native gold in quartz-barite aggregates while the next assemblage
is composed of goldfieldite and famatinite-luzonite. Later mineral assemblages
include: native gold with early tellurides, native tellurium with Au, Ag, Sb, and Bi
tellurides, and Cu and Fe sulfostannates (mawsonite, stannoidite, kesterite, nekrasovite, volfsonite, hemusite). A bismuth-sulfoselenide assemblage contains native
bismuth, Bi-selenides, sulfoselenides, sulfotellurides, and sulfoselenotellurides, and
Te and Se mineralogy
191
Fig. 3. Specimens showing mineral successions of the Kochbulak (a) and Kairagach
(b) deposits. (a): 1. altered andesite porphyry cluster, 2. quartz of the pre ore stage, 3.
quartz of the first ore stage, 4. matrix-banded quartz of the second ore stage. (b): 1. pre ore
alteration quartz-sericite-pyrite-carbonate rocks, 2. the first ore stage vuggy silica with
pyrite and disseminated native gold, 3. the second ore stage chalcedonic silica with native
gold (3a), and barite with goldtelluridesulphosalts mineralization (3b)
193
chalcopyrite. The Bi-sulfosalts assemblage consists of minerals of the bismuthiniteaikinite series. Near the end of the main ore stage, hessite, electrum, and chalcopyrite are common. Fahlores are intergrown with chalcopyrite to form aggregates
up to several millimeters in length and contain numerous inclusions of native gold,
Bi-sulfosalts, sulfostannates, tellurides, and selenides and minerals of the junoite
and pavonite homologue series (Plotinskaya and Kovalenker, 1998; Kovalenker
et al., 2003).
The main ore stage was formed at 120 to 309 C whereas telluride-bearing barite
and quartz formed at 150 to 240 C from low to moderately saline (0.913.4 wt.%
equiv NaCl) fluids dominated by Na and K (Plotinskaya et al., 2001; Kovalenker
et al., 2003).
Post-ore stage mineralization for both deposits consists of quartz-carbonatebarite veinlets that crosscut minerals of the preceding stages. These veinlets also
contain galena and sphalerite with rare chalcopyrite, pyrite, and tetrahedrite.
194
Native gold
Native gold from both deposits has a variety of morphologies: xenomorphic, elongate, lumpy, stringer-shaped, rounded, and oval. Grains vary in size from <2 mm in
the assemblage quartz sericite in the Kairagach deposit, to 23 mm in telluride
assemblages in the Kochbulak deposit. Native gold occurs in almost all mineral
assemblages and shows marked compositional variations (Tables 1 and 2, Fig. 5a
and b).
The main metal with which native gold forms an alloy is Ag (up to 46.0 wt.% in
Kochbulak and up to 46.6 wt.% in Kairagach), but it also contains Hg (up to
0.9 wt.% in Kochbulak and up to 11.3 wt.% in Kairagach), and Cu (up to
2.9 wt.% in Kochbulak and 2.4 wt.% in Kairagach). Most of the gold was deposited
in the assemblage quartz sericite or in chalcedonic silica prior to the deposition
of tellurides. As shown in Fig. 5a, each ore stage at Kochbulak commences with
native gold of very high fineness with a subsequent increase in Ag content from
early to late assemblages. A similar trend was observed for the second ore stage of
native gold in the Kairagach deposit (Fig. 5b). In places, relatively high Hg contents (up to 11.4 wt.%) were identified in veinlet-like electrum within fahlore grains
at Kairagach (assemblage 10 in Table 2 and Fig. 5b).
Gold and silver tellurides
Calaverite (AuTe2) is one of the most common tellurides in both deposits. At
Kairagach, it occurs within early assemblages of the second ore stage together
with native gold of high fineness, petzite, altaite (Fig. 4d), and, in places, with
tetrahedrite and tellurantimony. At Kochbulak, it is typically present in early assemblages of all three ore stages, and forms aggregates with native gold, petzite,
altaite, krennerite, and galena (Fig. 4b). Calaverite contains up to 1.8 wt.% Ag, up
to 0.9 wt.% Cu, and up to 3.0 wt.% Sb (Table 3).
Hessite (Ag2Te) is also a common telluride. At Kairagach, it occurs in contact
with native gold and chalcopyrite, whereas at Kochbulak it also coexists with
petzite, lillianite, and tetradymite (Figs. 4b and c). As a rule, it is confined to
mineral assemblages formed late in the paragenetic sequence. Stutzite (Ag5xTe3)
occurs in the same assemblages as hessite but is much less common. Petzite
(Ag3AuTe2) forms intergrowths with calaverite, hessite and native gold (Fig. 4e)
whereas sylvanite (AuAgTe4) is less common than the other precious metal tellurides but it occurs with native tellurium, empressite (AgTe), and Bi and Sb
tellurides (Fig. 4f), and rarely, with other AuAg tellurides. At Kairagach, sylvanite contains 1.94.7 wt.% Cu, which occupies an intermediate position in the
8
1
9
5
2
Quartz Sericite
Calaverite Altaite
Altaite Tellurobismutite
Coloradoite Chalcopyrite
Bismuthinite Tetradymite
11
10
Calaverite Krennerite
Sylvanite Altaite
Altaite Petzite Coloradoite
Tellurobismutite Melonite
Tellurantimony
Petzite Hessite Chalcopyrite
11
15
Assemblage
range
mean
range
mean
range
mean
range
mean
range
mean
range
mean
range
mean
range
mean
range
mean
range
mean
94.3899.70
97.90
90.2495.02
92.31
86.0688.25
87.15
79.8887.63
84.88
81.0782.61
81.74
75.5177.89
75.61
80.1285.35
81.93
50.31
93.4098.25
95.98
91.7793.61
92.45
85.5692.52
89.19
Au wt.%
0.005.68
1.84
2.6910.62
6.74
11.5011.93
11.71
11.4018.87
14.71
16.4518.25
17.64
20.9125.03
22.88
14.7719.06
17.41
45.98
0.466.40
3.21
5.527.62
6.51
7.6112.49
9.96
Ag wt.%
0.020.06
0.04
0.020.75
0.16
0.000.10
0.05
0.060.64
0.26
0.190.36
0.18
0.060.54
0.34
0.001.41
0.26
0.86
0.040.10
0.07
n.d.
0.040.49
Cu wt.%
0.100.52
0.32
0.090.29
0.20
0.060.40
0.23
0.050.15
0.11
0.110.33
0.19
0.150.16
0.15
0.17
0.000.87
n.d.
n.d.
<0.52
Hg wt.%
(continued)
35.3
28.1
23.9
19.7
11.7
3.3
61.2
27.8
16.9
11.3
6.4
Ag at.%
Table 1. Chemical composition of native gold and electrum from assemblages in the Kochbulak deposit (modified after Kovalenker et al., 1997)
Te and Se mineralogy
195
8
12
14
15
12
13
16
12
Assemblage
range
mean
range
mean
range
mean
range
mean
range
mean
85.1291.09
88.58
85.8388.22
87.16
79.4689.14
82.00
67.5076.82
72.26
55.9464.82
60.04
Au wt.%
6.7614.90
10.57
10.2913.38
12.03
11.5122.05
18.54
23.4332.28
27.29
35.2843.18
39.32
Ag wt.%
0.041.10
0.35
0.121.50
0.69
0.010.39
0.11
0.050.27
0.12
0.012.92
1.42
Cu wt.%
n number of analyses, n.d. not detected. Analyzed with Camebax-Micro (TsNIGRI) and Cameca SX50 (NHM)
Table 1 (continued)
0.020.07
0.05
0.000.32
0.13
0.000.21
0.12
0.120.61
0.35
n.d.
Hg wt.%
53.7
40.6
28.9
19.7
17.5
Ag at.%
196
O. Yu. Plotinskaya et al.
n
87.7999.41
97.40
87.2197.25
93.03
84.0497.01
92.24
86.3898.81
93.35
71.7895.48
86.89
82.5395.56
90.20
77.9495.22
85.80
72.0093.13
86.92
67.1182.69
78.64
40.0286.16
74.50
Au wt.%
0.1210.90
1.55
0.469.45
4.97
0.3915.35
5.17
0.4511.73
4.95
2.1827.14
11.39
1.0816.01
7.68
4.3220.26
12.58
6.4124.32
11.96
16.1529.26
19.69
12.3346.58
22.13
Ag wt.%
0.000.10
0.03
0.000.1
0.05
0.001.15
0.23
0.000.07
0.02
0.001.87
0.18
0.262.52
0.79
0.000.47
0.11
0.040.34
0.22
0.021.78
0.53
0.132.35
1.20
Cu wt.%
0.000.23
0.05
0.000.16
0.04
0.002.18
0.30
0.000.36
0.10
0.000.51
0.16
0.000.50
0.12
0.000.76
0.19
0.000.15
0.07
0.000.56
0.19
0.000.14
0.06
Pb wt.%
0.000.51
0.09
0.001.46
0.29
0.001.55
0.21
0.001.66
0.63
0.000.82
0.22
0.001.11
0.30
0.000.87
0.16
0.002.02
0.78
0.000.90
0.26
n.d
Bi wt.%
n number of analyses, n.d. not detected. Analyzed with Cameca MS-46 and Camebax SX-50 (IGEM RAS)
28 range
mean
8 range
mean
3 Altaite Calaverite
14 range
Petzite Chalcopyrite
mean
4 Tetradymite
7 range
Volyn-skite Chalcopyrite
mean
5 Bismuthite-Aikinite
25 range
Chalcopyrite
mean
6 Fahlore Chalcopyrite 26 range
CuFe-Sulfostannates
mean
7 Hessite Chalcopyrite
13 range
mean
8 Emplectite Chalcopyrite
4 range
mean
9 Chalcopyrite
12 range
mean
10 Fahlore
15 range
mean
1 Quartz Pyrite
Sericite
2 Quartz Barite
Assemblage
0.000.30
0.04
0.000.05
0.01
0.000.30
0.05
0.000.20
0.03
0.000.17
0.02
0.001.28
0.36
0.000.11
0.02
n.d.
Hg wt.%
19.3
20.7
12.9
18.7
8.4
8.9
8.7
2.8
Ag,at.%
0.000.10
0.02
0.000.62
0.10
0.002.70
0.23
0.000.24
0.05
0.000.07
0.02
0.000.19
0.04
0.000.36
0.05
n.d.
Te wt.%
Table 2. Chemical composition of native gold from different assemblages of the second ore stage of the Kairagach deposit
Te and Se mineralogy
197
198
Fig. 5. Ag contents of native gold from different mineral assemblages of Kochbulak (a) and
Kairagach (b) deposits. Q quartz; Ser sericite; Alt altaite; Bsm bismuthinite; Cld coloradoite; Cp chalcopyrite; CuFeSn sulfostannates of Fe and Cu; Cv calaverite; Empl
emplectite; Fhl fahlores; Hs hessite; Kr krennerite; LHS sulphosalts of lillianite series;
Ml melonite; Ptz petzite; Py pyrite; Sv sylvanite, Tat tellurantimony; Tbs tellurbismuthite;
Te native tellurium; Trd tetradymite; Vol volynskite
0.00
0.14
0.09
0.05
0.64
61.96
41.29
44.51
12.96
7.72
10.64
19.14
0.48
0.27
0.86
0.46
0.65
0.50
0.71
0.00
0.29
0.15
0.29
0.22
0.06
0.06
0.03
0.00
0.06
0.04
0.06
0.15
0.00
0.37
41.46
0.17
24.06
0.01
24.74
25.62
28.41
0.01
0.13
0.01
Au
Pb
Fe
Hg
Cu
Sb
Te
Se
Total
n Ag
Bi
0.00
0.00
0.00
0.00
0.01
0.00
0.01
0.00
0.00
0.00
0.94
0.00
0.96
0.00
1.01
1.04
1.19
0.00
0.00
0.00
Au
0.00
0.00
0.00
0.00
0.00
0.37
0.00
0.00
0.00
0.00
0.03
0.01
0.01
0.00
0.00
0.00
0.15
0.05
0.06
0.00
0.09
0.04
0.00
Cu
0.00
0.00
0.00
0.00
Fe
0.01 0.00
0.03
0.00 0.00
0.01 0.01
0.01 0.00
0.73 0.00
0.00 0.00
0.01 0.00
0.03 0.00
0.00 0.01
0.04 0.00
0.00 0.00
0.01 0.02
0.01 0.01
0.99 0.00
0.83 0.06
0.00 0.95
0.00 0.00
0.00
0.00
0.00
0.00
Pb
0.01
0.99
0.00
0.00
0.02
0.00
0.00
0.01
0.01
0.01
0.00
0.00
0.00
Hg
0.02
0.01
0.01
0.01
0.02
0.03
0.00
0.01
0.02
0.02
0.03
0.05
0.09
1.99
0.76
0.24
0.03
0.01
0.00
0.01
Sb
Te
1.99
0.99
2.00
1.00
4.00
3.98
3.95
0.97
1.97
1.95
1.98
1.95
1.96
2.06
3.98
1.90
2.98
1.87
2.94
0.00
2.93
1.22
2.93
1.74
2.07
1.88
1.69
3.83
0.00
1.08
0.00
0.00
0.96
0.00
0.00
0.00 0.01 1.99
0.00 0.01 0.99
0.00
0.00
0.00
0.00
0.00
0.00
Bi
0.01
0.01
0.01
0.09
0.17
0.03
0.02
0.02
0.01
0.01
0.88
0.81
2.15
0.24
0.02
0.73
0.00
0.00
0.00
0.00
0.00
0.00
Se
0.00
0.00
0.00
0.00
0.00
0.00
0.02
0.01
0.91
0.85
0.00
0.01
0.01
0.00
0.00
0.01
0.38
0.76
0.59
0.01
0.28
0.00
0.00
Note: Cameca MS 46, other analyses Cameca SX 50; n number of atoms; 1 calaverite; 2 hessite; 3 petzite; 4 empressite; 5 sylvanite; 6 Cu-sylvanite,
7 krennerite; 8 volynskite; 9 tetradymite; 10 Se-tetradymite; 11 rucklidgeite; 12 phase Bi2Te3; 13 tellurobismuthite; 14 tellurantimony; 15 (Bi,Sb)2Te3;
16 (Bi,Sb)2,Te2Se; 17 kawazulite; 18 laitakariite; 19 Bi (S,Se); 20 altaite; 21 clausthalite; 22 frohbergite, 23 coloradoite; 24, 25 native Te
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Ag
Table 3. Representative electron microprobe analyses of tellurides and selenides from the Kochbulak and Kairagach deposits
200
AuAg tellurides, and native gold. Tetradymite contains up to 4 wt.% Se. Rare
rucklidgeite (PbBi2Te4) and tellurobismuthite (Bi2Te3) occur with tetradymite in
both the Kochbulak and Kairagach deposits. Joseite [Bi3Te(Se,S)] and tsumoite
(Bi3Te2Se) occur at Kochbulak whereas sulfotsumoite [Bi3Te2(S,Se)] occurs at
Kairagach. Kawazulite (Bi2Te2Se) and Sb-kawazulite [(Bi,Sb)2Te2Se] were observed at Kairagach in intergrowths with native tellurium. An unnamed mineral
with the formula [(Bi,Sb)2Te3], occurs within empressite, sylvanite and tetradymite
at the Kochbulak deposit. It is presumably transitional within the tellurobismuthite
(Bi2Te3)-telluroantimony (Sb2Te3) isomorphic series. Other unnamed phases with
the following formulas: AgBi3Te5, Ag3Bi5Te9, and Pb2Bi6Te11 were reported at
Kochbulak by Kovalenker et al. (1980, 1997).
Bismuth selenides and sulfoselenides were observed only in ores from Kairagach.
These minerals are guanajuatite (Bi2Se3), laitakarite [Bi4(S,Se)3], nevskite [Bi(Se,S)]
and unnamed phases with formulae CuBi3(S,Se)5 and Cu2Bi15(S,Se)11. The following
unnamed phases Bi2SeS, Bi3TeSe and Bi3Te2SeS were also reported by Spiridonov
and Badalov (1983).
Lead tellurides and selenides
Altaite (PbTe) is as abundant as calaverite and hessite and occurs in both deposits
in an assemblage with calaverite and native gold. Clausthalite (PbSe), as well as
Se-rich galena [Pb(S,Se)] with S contents from 2.4 to 11.6 wt.% occurs at the
Kairagach deposit in assemblages with famatinite-luzonite, Te-tetrahedrite, chalcopyrite, and CuFe-sulfostannates. At Kochbulak, small (<5 mm) single grains of
Se-rich galena from the first ore stage were identified by EDX in an assemblage
with chalcopyrite, tetrahedrite, famatinite, and goldfieldite.
Other tellurides and selenides
Coloradoite (HgTe) and frohbergite (FeTe2) occur at both deposits but are relatively rare and spatially associated with the same minerals as altaite. Telluroantimony (Sb2Te3) occurs in both deposits in assemblages with calaverite, native
tellurium, and Sb-kawazulite. Melonite (NiTe2) occurs with altaite, petzite, and
coloradoite only within the first ore stage at the Kochbulak deposit.
Cu tellurides vulcanite, (CuTe), rickardite (Cu7Te5) and weissite (Cu5Te3) were
found in the Kochbulak deposit as intergrowths with covellite, chalcocite, and
tellurite (TeO2) and are presumably of supergene origin.
Native tellurium
Native tellurium was found at both deposits. At Kairagach, it occurs as intergrowths
with tellurantimony, calaverite, Cu-sylvanite, clausthalite, and Sb-kawazulite
where, in places, it is overgrown by chalcopyrite. At shallow levels, native Te
contains up to 10.3 wt.% Se and up to 0.5 wt.% Sb whereas at deep levels it
contains up to 0.2 wt.% Se and up to 0.7 wt.% Sb. At the Kochbulak deposit native
Te occurs mostly within the first ore stage in pipe-like ore bodies where it forms
Te and Se mineralogy
201
202
Fig. 7. Log f O2 versus pH diagram for the stabilities of calaverite and hessite (hatched
areas), barite (dotted lines), calcite (dashed lines), and for minerals of the FeSO system
(dashed-dotted lines) for the following conditions: Au 1 ppb, Ag 1 ppb, Te 1 ppb,
and S 0.01 m. Arrows show general temporal trends for Kochbulak (1) and for Kairagach
(2). Sources of data are listed in text
or by a decrease in fO2 (trend 2 on Fig. 7). All three processes may have taken
place as tellurides formed at Kochbulak and Kairagach. At the same time, an abundance of barite and the presence of calcite within the main ore stage of Kairagach
suggests that fO2 was maintained at a relatively high level (>35 log fO2 units for
250 C). Thus the evolution of telluride assemblages at Kairagach was caused by
an increase in pH (trend 2 on Fig. 7 was dominant). Barite and calcite are rare in
ore assemblages at Kochbulak, whereas sulfides (pyrite and chalcopyrite) are more
abundant than at Kairagach and suggests that a decline in log fO2 to 40 could
have been the main factor in the changing the dominance of calaverite to hessite as
the main precious metal telluride (i.e. trend 1 on Fig. 7 was dominant within each
ore stage).
According to the experimental studies of Cabri (1965), the assemblage native Te sylvanite at both deposits and the assemblage native Te krennerite at
Kochbulak, suggest that they formed below 335 C. Temperature estimates using
the assemblage native Te sylvanite empressite cannot be made since it was not
reported in the experimental studies of Pellini (1915), Markham (1960), Cabri
(1965), and Legendre et al. (1980). However, Cabri (1965) reported that the assemblage native Te sylvanite st
utzite is stable at 290 C, which is in good agreement with the fluid inclusion data.
Thermodynamic data for sulfides and tellurides by Barton and Skinner (1979)
and Afifi et al. (1988) were used to calculate phase boundaries in Fig. 8. At the
beginning of telluride deposition at approximately 250 C, log f S2 (14.6 to 8.6)
was controlled by the stability of pyrite and chalcopyrite. log f Te2 for the formation
of native Te, calaverite and tellurantimony was >7.8 (area 1 in Fig. 8a) and
decreased to a minimum of approximately 11.5 log units during the deposition
Te and Se mineralogy
203
Fig. 8. Log f Te2 versus log f S2 diagrams calculated for 250 C (a) and 150 C (b). 1. native
Te calaverite tellurantimony, 2. native gold altaite and native gold calaverite,
3. native gold Bi tellurides, 4. native gold Bi sulfosalts, 57. hessite native gold with:
5. 10 to 32 at.% of Ag (Kairagach), 6. 28 to 35 at.% of Ag and 7. 40 to 60 at.% of Ag
(Kochbulak). Arrows show general trends for Kochbulak (1) and Kairagach (2). Sources of
data are listed in text
of native gold altaite calaverite (area 2 on Fig. 8a) and further to a minimum of
13 where the assemblage native gold tellurobismuthite was stable.
As the temperature decreased to 150 C, coexisting pyrite and chalcopyrite are
stable between log f S2 22.0 and 13.6 (Fig. 8b). Since they coexist with native
gold, galena and tellurobismuthite this suggests that log f Te2 was constrained to
between 18.0 and 13.6 (area 4 on Fig. 8b).
Later-formed assemblages contain native gold coexisting with hessite. Using
the thermodynamic data of Afifi et al. (1988) and assuming that the Ag content was
buffered only by f Te2 allows f Te2 to be determined. For native gold associated with
hessite from the Kairagach deposit, Ag contents range from 10 to 28 at.% (mean
20.7 at.%), which corresponds to values of log f Te2 that range from 18.9 to 11.6
(area 5 on Fig. 7a). At Kochbulak, the Ag content of native gold ranges from 28 to
35 at.% in the assemblage native gold hessite chalcopyrite and from 40.6 to
61.2 at.% for the assemblage native gold hessite lillianite. Values of logTe2
range from 19.3 to 18.2, and from 22.5 to 20.1 for these assemblages, respectively. Thus, at Kochbulak the deposition of native gold and Ag tellurides was
accompanied by a drop in f Te2 of five orders of magnitude whereas f S2 likely
remained constant (trend 1 on Fig. 7a). At the Kairagach deposit, f Te2 could have
been constant or decreased slightly as f S2 increased (trend 2 on Fig. 8a). In general,
paragenetic sequence of telluride assemblages during each ore stage at both.
Kochbulak and Kairagach was the result of a decrease in temperature and log f Te2.
At Kairagach, selenides and sulfoselenides of Bi and Pb are common, in contrast to the Kochbulak deposit, where only Bi and Pb telluroselenides and sulfotelluriselenides were formed. Despite the absence of thermodynamic data for some
204
Fig. 9. Log fSe2 versus log f Te2 (a) and versus log f S2 (b) diagrams calculated for 300 C.
Shaded areas show the stability fields of selenides, tellurides, and sulfides at Kochbulak (1)
and Kairagach (2) deposits. Sources of data are listed in text
minerals in the systems BiTeSe and BiSTe, the ore forming conditions can be
estimated from the stability fields of guanajuatite (Bi2Se3) and clausthalite (PbSe)
and data from Barton and Skinner (1979) and Simon and Essene (1996) (Fig. 9a
and b). Values of log fSe2 14.0 to 6.5 and log f Te2 11.0 to 6.2 are obtained for the Kairagach deposit at 300 C based on the presence of guanajuatite,
clausthalite and hessite (rather than naumannite). At Kochbulak, the value of
log f Se2 was <8.5.
The values of f S2, f Te2, and f Se2 may be reflecting multiple inputs of magmatic
components into the Kochbulak ore-forming system while a magmatic contribution
to the Kairagach ore-forming system is less apparent. The precipitation of sulfides,
tellurides, and selenides were associated with decreasing f S2 and f Te2 and increasing f Se2 conditions.
The deposition of abundant native gold of high fineness preceded telluride
deposition in both deposits. Native gold has higher Ag contents where spatially associated with tellurides, as well as with lillianite at Kochbulak or fahlores and chalcopyrite at Kairagach. As noted by Afifi et al. (1988), in most epithermal deposits
native gold usually precipitates either with or follows the deposition of tellurides.
This has been observed at, for example, Golden Sunlight, Montana (Porter and
Ripley, 1985), and Emperor, Fiji (Pals and Spry, 2003). However, in some high
sulfidation deposits (e.g., Elshitsa and Radka deposits, Bulgaria, Bogdanov et al.,
1997), native gold precipitated in the early quartz-pyrite stage, which is similar to
that observed in the Kochbulak and Kairagach deposits. The most plausible explanation for this observation is that at the beginning of each stage of hydrothermal
activity the initial f S2=f Te2 ratio was too high and allowed only sulfides and native
gold to be deposited with the residual fluid being enriched in Te.
Te and Se mineralogy
205
Conclusions
1. Tellurides at Kochbulak are more abundant and variable than at Kairagach but
they occur in similar assemblages and three ore stages. The generalized telluridebearing sequence is: 1. altaite Au tellurides native Te, 2. calaverite native
gold, 3. Bi tellurides AuAg tellurides native gold, followed by 4. Ag
tellurides native gold.
2. The Ag content of tellurides and native gold increases from early to late in the
paragenetic sequence, which corresponds to a decrease in temperature and fO2,
and a concomitant increase in pH.
3. Values of log f Te2 ranged from 13.0 to 7.8 at the beginning of telluride
deposition (around 250 C) and decreased to <20 as the temperature declined.
4. The main difference in telluride and selenide assemblages between the two
deposits is the presence of selenides and sulfoselenides of Bi and Pb at the
Kairagach deposit which was, in part, caused by higher f Se2 conditions compared to those observed at Kochbulak.
Acknowledgements
The authors would like to thank A. Tsepin, V. Malov, N. Troneva (IGEM RAS, Moscow),
S. M. Sandomirskaya (TsNIGRI), T. Williams, J. Spratt and A. Kearsley (Natural History
Museum, London) for the electron microprobe analyses. OP is thankful to V. L. Rusinov and
A. V. Zotov (IGEM RAS) for their assistance and advice with thermodynamic calculations.
This paper was greatly improved by the reviews of P. Spry and E. Ronacher.
This study was supported by the Natural History Museum, London through a CERCAMS
project, by the Russian Foundation for Basic Research (project Nr 04-05-64407), and by the
Russian Science Support Foundation. The research is a contribution to IGCP projects #473
and #486.
References
Afifi AM, Kelly WC, Essene EJ (1988) Phase relations among tellurides, sulfides, and oxides:
I. Thermochemical data and calculated equilibria; II. Applications to telluride-bearing
ore deposits. Econ Geol 83: 377394 and 395404
Badalov AS, Spiridonov EM (1983) Fahlores and native gold of the Kairagach mineralization
(Eastern Uzbekistan) (in Russian). Uzb Geol Zh 2: 7478
Badalov AS, Spiridonov EM, Heinke VP, Pavshukov VV (1984) Minerals-native elements and
tellurides of the Kairagach volcanic-hosted mineralization (Uzbek Soviet Socialist
Republic) (in Russian). Zap Uzb Otd Vses Min O-va 37: 6467
Barton PB Jr, Skinner BJ (1979) Sulfide mineral stabilities. In: Barnes HL (ed) Geochemistry of hydrothermal ore deposits. Wiley Interscience, New York, pp 278403
Bogdanov K, Tsonev D, Kuzmanov K (1997) Mineralogy of gold in the Elshitsa massive
sulphide deposit, Sredna Gora zone, Bulgaria. Mineral Deposita 32: 219229
Bonham HF Jr (1986) Models for volcanic-hosted epithermal precious metal deposits: a
review. Int Volcanol Congress Symp 5. Proceedings, Hamilton, New Zealand, pp 1317
Cabri LJ (1965) Phase relations in the AuAgTe system and their mineralogical significance. Econ Geol 60: 15691606
Dalimov TN, Ganiev IN (1994) Zoning of magmatism in the Chatcal-Kurama region
(Devonian, Middle Carbon) (in Russian) Uzb Geol Zh 3: 2834
206
Genkin AD, Kovalenker VA, Safonov YG (1980) Characteristics of the ore textures and
formation mechanism of pipe-like ore bodies of the Kochbulak deposit, Methods of
investigation of ore-forming sulfides and their parageneses (in Russian). Moscow: Nauka
127139
Heald P, Foley NK, Hayba DO (1987) Comparative anatomy of volcanic-hosted epithermal
deposits: acidsulfate and adularia-sericite types. Econ Geol 82: 126
Henley RW (1991) Epithermal gold deposits in volcanic terranes. In: Foster RP (ed) Gold
metallogeny and exploration. Blackie, Glasgow, pp 133164
Islamov F, Kremenetsky A, Minzer E, Koneev R (1999) The KochbulakKairagach ore field.
In: Shayakubov TSh, Islamov F, Kremenetsky A, Seltmann R (eds) Au, Ag, and Cu
deposits of Uzbekistan. Excursion Guidebook, Potsdam GFZ, pp 91106
Koneev RI, Gertman YL (1997) Microparageneses of gold in gold-ore formations of Eastern
Uzbekistan. Osnovnye problemy v uchenii o magmatogennykh rudnykh mestorozhdeniyakh (Principle problems in the science on magmatic ore deposits). Moscow: Inst Geol
Rudn Mest Ross Akad Nauk: 142143 (in Russian)
Kovalenker VA, Chernyshev IV, Plotinskaya OY, Prokofev VY (2004) Ore mineralogy, fluid
inclusions, age and isotopic characteristic of the late-Paleozoic high-sulfidation epithermal gold-telluride deposits: Kurama Mountains, Middle Tien Shan. In: Cook J,
Ciobanu CL (eds) AuAg-telluride Deposits of the Golden Quadrilateral, South Apuseni
Mts., Romania, Guidebook of the International Field Workshop of IGCP project 486,
IAGOD Guidebook Series,: 12: 239241
Kovalenker VA, Heinke VP (1984) A new CuSnBiSe type of mineralization in the
Kurama subzone of the Central Tien Shan (in Russian). Izv Akad Nauk SSSR, Ser Geol
5: 91104
Kovalenker VA, Naumov VB, Prokofev VYu (1980) Mineralogical and geochemical regularities and PT parameters of the origin of productive mineral assemblages of the
Kochbulak ore field (in Russian). Geol Ore Dep 1: 3852
Kovalenker VA, Plotinskaya OY, Prokofev VY, Gertman YL, Koneev RI, Pomortsev VV
(2003) Mineralogy, geochemistry, and genesis of goldsulfideselenidetelluride ores
from the Kairagach deposit (Uzbekistan). Geol Ore Dep 45: 171200
Kovalenker VA, Safonov YG, Naumov VB, Rusinov VL (1997) The Kochbulak epithermal
goldtelluride deposit (Uzbekistan). Geol Ore Dep 39: 127152
Kovalenker VA, Troneva NV, Dobronichenko VV (1980) Characteristics of main ore minerals
from pipe-like ore bodies of the Kochbulak deposit (in Russian). In: Distler VV (ed)
Methods of investigation of ore-forming sulfides and their parageneses Moscow: Nauka:
140164
Kovalenker VA, Troneva NV, Kuzmina OV, Vyalsov LN, Goloshchukov PM (1979) The
first finding of kostovite in the Soviet Union (in Russian). Dokl Akad Nauk SSSR 247:
564569
Legendre B, Souleau C, Chhay H (1980) The ternary system AuAgTe. Bull Soc Chim
France 56: 197204
Markham NL (1960) Synthetic and natural phases in the system AuAgTe. Econ Geol 55:
11481178
Pals DW, Spry PG (2003) Telluride mineralogy of the low sulfidation epithermal Emperor
gold deposit, Vatukoula, Fiji. Mineral Petrol 79: 285307
Pellini G (1915) Telluriri di argento e oro. Gaz Chim Ital 45: 469484
Plotinskaya OY, Kovalenker VA (1998) The Kairagach epithermal goldtelluride deposit:
mineralogicalgeochemical zonation. Tez Dokl Nauch Konf Zolotorudnye mestorozhdeniya Uzbekistana:geologiya i promyshlennye tipy (Proc. Conf Gold-ore deposits of
Uzbekistan: geology and commercial types). Tashkent, IMR, pp 5760 (in Russian)
Te and Se mineralogy
207
Plotinskaya OY, Kovalenker VA, Prokofev VY, Groznova EO, Nosik LP (2001) Formation
conditions of ores in the Kairagach epithermal goldtelluride deposit (Uzbekistan):
fluid inclusions and stable isotopes. In: Melnikov FP, Poliansky EV (eds) Trudy X
Mezhdunarodnoi konferentsii po termobarogeokhimii (Proc. X Int Conf on Thermobarochemistry) Aleksandrov: VNIISIMS, pp 158179 (in Russian)
Porter EW, Ripley E (1985) Petrologic and stable isotope study of the gold-bearing breccia
pipe at the Golden Sunlight deposit, Montana. Econ Geol 80: 16891706
Simon G, Essene EJ (1996) Phase relations among selenides, sulfides, tellurides, and oxides:
I. Thermodynamic properties and calculated equilibria. Econ Geol 91: 11831208
Spiridonov EM, Badalov AS (1983) New bismuth sulfoselenotellurides and sulfoselenides
from the Kairagach volcanic deposit (Eastern Uzbekistan) (in Russian). Uzb Geol Zh 6:
8284
White NC, Hedenquist JW (1990) Epithermal environments and styles of mineralization:
variations and their causes, and guidelines for exploration. J Geochem Explor 36:
445474
Zhang X, Spry PG (1994) Calculated stability of aqueous tellurium species, calaverite and
hessite at elevated temperature. Econ Geol 89: 11521166
Zonenshain LP, Kuzmin MI, Natapov LM (1990) Geology of the USSR: A plate tectonic
synthesis. AGU Geodynam Ser Monogr 21, 240 p
Authors addresses: O. Plotinskaya (corresponding author; e-mail: plotin@igem.ru,
olgaplotin@yahoo.co.uk) and V. A. Kovalenker, Institute of Geology of Ore Deposits,
Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences (IGEM RAS),
Staromonetny per. 35, 119017 Moscow, Russia; R. Seltmann and C. J. Stanley, CERCAMS,
Department of Mineralogy, Natural History Museum (NHM), Cromwell Road, London SW7
5BD, United Kingdom