Ore Petrography and Chemistry of the Tellurides from the Dongping Gold Deposit, Hebei Province, China

Home , Altaite, Calaverite, Krennerite, Petzite, Telluride (chemistry), Tellurobismuthite

Ore Geology Reviews 64 (2014) 23–34

Contents lists available at ScienceDirect

Ore Geology Reviews

journal homepage: www.elsevier.com/locate/oregeorev

Ore petrography and chemistry of the tellurides from the Dongping gold deposit, Hebei Province, China

Shen Gao, Hong Xu ⁎, Desen Zhang, Henan Shao, Shaolong Quan

School of Earth Science and Resources, China University of Geosciences (Beijing), Beijing 100083, China article info abstract

Article history: The Dongping gold deposit is a mesothermal lode gold deposit hosted in syenite. The ore petrography and chem- Received 5 March 2014 istry of the tellurides from the alteration zone of the deposit have been studied in detail using optical microscopy, Received in revised form 5 June 2014 scanning electron microscopy, electron probe micro-beam and X-ray diffraction facilities. The tellurides, Accepted 12 June 2014 consisting mostly of calaverite, altaite, petzite tellurobismuthite and tetradymite, are hosted irregularly in pyrite Available online 19 June 2014 fractures and voids. In the ore bodies, the species and quantity of tellurides decrease from the top downwards, fi Keywords: accompanied with lowering of gold neness, and the existence of tellurides exhibits a positive correlation with Tellurides gold enrichment. Mineral paragenesis and chemical variations suggest that during evolution of the ore- Ore petrography forming fluids Te preferably incorporated with Pb to form altaite, followed in sequence by precipitation of petzite, Chemistry and calaverite when Ag has been exhausted, and the residue fluids were enriched in Au, giving rise to formation Gold Deposit of native gold. Calculation with reference of the fineness of native gold coexisting with the tellurides indicates Dongping that at 300 °C, log f (Te2) varied between −8.650 and −7.625. Taking account of the Au–Ag–Te mineral paragen- China esis, it is inferred that log ƒ (Te2) varies from −9.12 to −6.43, log ƒ (S2) −11.47 to −8.86. In consideration of the physicochemical conditions for formation of tellurides, with comparison to some known telluride deposits, it is

1. Introduction alteration. The ores were formed during the early Cretaceous, with U–Pb weighted average age of 140.3 ± 1.4 Ma (Li et al., 2010). The temperature Tellurium commonly occurs as a dispersed element, incorporating of ore-forming process has been constrained as 263–342 °C (Fan et al., Au, Ag, Cu, Pb, Zn, Hg, Bi, Ni, and PGE, etc., to form tellurides. These tel- 2001), and the ore-forming fluids have been interpreted as mixing of me- lurides have been found in many gold deposits, e.g., the Cripple Creek teoritic water with deep-derived fluids (Bao and Zhao, 2006). The ores are deposit, USA, Emperor deposit, Fuji, Roşia Montană gold deposit, sulfide-poor and telluride-rich (Song and Zhao, 1996), with metallic min- Romania (Pals and Spry, 2003; Thompson et al., 1985; Wallier et al., erals less than 5%. Most tellurides in the ores are dispersed as micron- 2006), Guilaizhuang, China, Xiaoqinling gold deposit, China (Fang and sized grains in the other ore minerals (Zhang et al., 2002). The previous Shuai, 1988; Hu et al., 2005), Dashuigou telluride deposit, China (Mao studies have identified calaverite, petzite, altaite, hessite, krennerite and et al., 1995a, 1995b), and Sandaowanzi telluride gold deposit, China stutzite in the auriferous quartz veins from the upper of the ore bodies (Liu et al., 2011; Zhao et al., 2010). Telluride-rich gold deposits in the (Song and Zhao, 1996; Zhang et al., 2002). The telluride mineralogy in world have been studied intensively, on their mineralogy, paragenesis, the lower part of the deposit, however, is poorly understood, and the chemistry, physicochemistry conditions of ore-forming fluids, solid occurrence and spatial distribution of tellurides have not been examined exsolution-based temperature indicator (Xu et al., 2011, 2012; Yu et al., in detail. The authors conducted detailed study, using optical microscope 2012), and geochemistry of major and trace elements of the ore bodies, observation, scanning electron microscope, electron probe, X-ray diffrac- basedonwhichthesourceofore-formingfluids could be speculated. tion analysis and other microscopic analysis facilities, on the chemistry Discovered in the 1980s, the Dongping gold deposit is a mesothermal and petrography of the tellurides in the alteration-hosted ores, which quartz vein and potassic alteration-relatedgolddeposit.Theorebodies provides evidence for the telluride-forming environment and the genetic in the upper part of the deposit comprise quartz veins whereas the ores link between tellurides and native gold. bodies in the lower part, e.g., ore body, No. 70, are associated with potassic 2. Geological Setting

⁎ Corresponding author. E-mail addresses: [email protected] (S. Gao), [email protected] (H. Xu), The Dongping gold deposit is located in the central section of the [email protected] (D. Zhang), [email protected] (H. Shao), [email protected] (S. Quan). northern margin of North China Craton. The regional stratigrapgy

Fig. 1. Geological sketch map of the area around the Dongping gold deposit in Hebei province. (Modiﬁed after Li et al., 2010; Song and Zhao, 1996).

comprises the Neoarchean Sanggan Group, Paleoproterozoic source (Zhang, 1996). It has been proposed that the mineralization Hongqiyingzi Group, Mesoproterozoic Changcheng Group, Jurassic was associated with the alkaline intrusion and relevant hydrothermal and Quaternary. The deposit is controlled by the intersection of NNE- events (Nie et al., 2004). and NW-striking faults, and hosted in Hercynian Shuiquangou alkaline The Neoarchean Jiangouhe Formation, Sanggan Group has experi- igneous complex that emplaced in the Jiangouhe Formation (Fig. 1). enced amphibolite-granulite facies metamorphism, (Fig. 2)andtheli- LA-ICP-MS zircon U–Pb dating suggests that this alkaline complex thology is dominated by amphibole gneisses, amphibolite and leptites. emplaced at 382.8 ± 3.3 Ma (Li et al., 2010). Geochemical studies The deposit is hosted in the syenite within the Hercynian Shuiquangou show that the extensive granitic aplite veins cut by pegmatite veins alkaline complex. U–Pb dating of hydrothermal zircon yielded 140.3 ± and the Shuiquangou complex were derived from the same magma 1.4 Ma (Li et al., 2010). There are 70 gold zones or swarms in the mining

Fig. 2. Simpliﬁed geological map of the Dongping gold deposit (modiﬁed after Zhang et al., 2012; Zijin Mining in Chongli, 2011). S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34 25

Fig. 3. (a) and (b) Geological cross-sections through Dongping gold deposit. (After Zijin Mining in Chongli, 2011). area (Fig. 2). This study focuses on ore body Nos. 70, 71, and 73, of which replaced by tetradymite, tellurobismuthite and galena. Gangue minerals No. 70 is the largest one which occurs as veins and stripes (Fig. 3), with include K-feldspar, albite and quartz, with subordinate sericite, epidote, Au grade averaging 3.79 g/t. chlorite, calcite, kaolinite, and barite. Quartz and pyrite are the major The ore bodies consist of poly-metallic sulfide quartz veins in the gold-bearing minerals, and the subordinate gold-bearing minerals upper part with zones of potassic alteration in the lower part (Fig. 4). include magnetite, hematite, chalcopyrite, calaverite, petzite, altaite The metallic mineral content is less than 3%, and is dominated by pyrite, and galena. galena, sphalerite, chalcopyrite, covellite, hematite, magnetite and Four mineralization stages could be identified from field observations: limonite. The native gold and tellurides are fine-grained, hosted in (i) an early silica-potassium alteration stage, with little sulfides and no quartz and pyrite. The tellurides consist of calaverite, petzite, altaite, significant gold mineralization. This stage is expressed as milky quartz tellurobismuthite and tetradymite. Calaverite, petzite, and altaite are and reddish potassium feldspar veins crosscutting the syenite and potas- granular and brecciated, coexisting with native gold that is in turn sium feldspar alteration in the wall rocks. (ii) Pyrite–quartz stage:

Fig. 4. Ore types of the Dongping gold deposit, (a)—gray quartz vein included sulﬁdes. (b)—Silicated and K-feldspathization rock. (c)—Gold ore of quartz vein type. (d)—GOLD ore of altered rock type. 26 S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34

Fig. 5. Distribution of studied samples in orebody 70. expressed as milky quartz veins or veinlets in the potassium alteration an X-ray beam diameter of 30 μm. The data was collected after 2 h rocks, containing coarse-grained cubic pyrite, magnetite, hematite, and the 2θ ranged from 20° to 160°. The accuracy of d-values is better chalcopyrite and galena. (iii) polymetallic sulfide–quartz stage: the prin- than 0.001 Å. cipal gold mineralization stage, expressed as quartz veins containing pyrite, galena, chalcopyrite, sphalerite and telluride veinlets crosscutting 4. Ore petrography of tellurides and native gold the early quartz veins. (iv) Carbonate–quartz stage: expressed as quartz and calcite veinlets and stockworks, with a small amount of sericite, 4.1. The tellurides barite, chlorite and epidote. This stage is not significantly related with the gold mineralization. The investigated samples were taken from the ore body No. 70, in Wall rock alteration associated with gold mineralization includes the potassic and silica alteration zone. Field observations suggest that K-feldspathization, silicification and pyritization, and less significantly the tellurides were mostly formed in stage III, associated with sulfides. sericite, carbonate, barite, epidote and kaolinite. Optical microscopy and electron probe show that the sulfides are pyrite, chalcopyrite, galena, sphalerite, while tellurides consist of altaite, 3. Sample collection and analytical methods petzite, calaverite, tellurobismuthite and tetradymite. The tellurides exist mostly as blebs enclosed in quartz and pyrite, and less commonly 498 samples were collected from levels 1264, 1224 and 1184 of the in fractures of pyrite, with a small amount in between grains of magne- No. 70 vein swarm in the lower part of alteration zone, representative of tite and hematite (Fig. 6). vertical and lateral variations (Fig. 5). Using microscope and scanning The electron microprobe and X-ray diffraction analyses of the tellu- electron microscopy, and X-ray powder diffraction methodology, we rides are given in Tables 1, 3 and Fig. 9. The analyses reveal that the examined the morphology and textures of the ores, and the chemical calaverite is composed of 41.92% Au and 55.13% Te, and the chemical composition of native gold and tellurides, using electron microprobe. formula can be constrained as Au0.99Te2.01, abbreviated as AuTe2. Scanning electron microscope analysis was carried out at the Compared with the calaverite from Sandaowanzi telluride-gold deposit

JEOL JSM-6510A scanning electron microscope equipped with back- (AuTe2: Au: 43.59%, Te: 56.41%, Yu et al., 2012), the calaverite from scattered imaging, at the School of Materials Science and Engineering, Dongping is relatively low in gold. Beijing University of Sciences and Technology. The altaite contains 60.08% Pb, and 37.71% Te, with a chemical

Electron microprobe analyses (EMPA) was carried out at the JEOL formula expressed as Pb0.99Te1.17, relatively low in lead compared with JXA-8230 electron microprobe laboratory, the Institute of Mineral the published standard (PbTe2: Pb: 61.91%, Te: 38.09%, Wang, 1987). Resources, Chinese Academy of Geological Sciences. Operation was The petzite contains 24.21% Au, 42.29% Ag, and 32.55% Te, under acceleration voltage of 20 kV, a beam current of 20 nA and with a chemical formula expressed as Ag3.05Au0.96Te1.99, abbreviated beam diameter of 5 μm. The standards used for calibration: Pd/Au as Ag3AuTe, which is basically identical to the published standard alloy for Au; AgS for Ag; HgTe for Te; CuFeS2 for Fe, Cu and S; FeAsS, (Ag3AuTe2: Ag: 41.71% Au: 25.42%, Te: 32.87%, Wang, 1987). Sb2S3, PbS and ZnS for As, Sb, Pb and Zn, respectively. Tellurobismuthite occurs as small isolated grains up to 300 μmin Due to the tiny size of telluride minerals, the samples were analyzed length. It occurs mainly as irregular grains coexisting with native gold under the Rigaku D/max Rapid IIR 18 KW Rotating anode micro-zone (Fig. 7a). diffraction, at the research center of X-ray diffraction of Central The tellurobismuthite contains 52.95% Bi and 47.97% Te. The chemi-

South University. The working condition was 45 kV and 35 mA with cal formula of tellurobismuthite can be expressed as Bi2.01Te2.99, S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34 27

Fig. 6. Reﬂected light photomicrographs of Au–Ag–Te–Pb tellurides from the Dongping gold deposit, (a)—coexistence of calaverite with native gold. (b)—Coexistence chalcopyrite, petzite, calaverite with native gold. (c)—Coexistence of chalcopyrite, altaite with native gold. (d)—Native gold intergrown with altaite. (e)—Coexistence chalcopyrite, altaite, petzite, calaverite with native gold. (f)—Coexistence of altaite, petzite, calaverite with native gold. (g)—Petzite, calaverite with native gold. (h)—Petzite with calaverite. Au—Native gold. Cav—Calaverite. Ptz—Petzite. Alt—Altaite. Py—pyrite. Cp—Chacopyrite. Qz—Quartz. Cal—Calcite.

abbreviated as Bi2Te3, which is identical to the published data (Bi2Te3: The tetradymite contains 59.37% Bi, 36.78% Te, and 4.10% S. The Bi: 52.09%, Te: 47.91%) (Wang, 1987). chemical formula of tetradymite can be expressed as Bi2.03Te2.05S0.91, Tetradymite is not abundant in the ores, and has been found as small abbreviated as Bi2Te2S, which is identical to the tetradymite from grains up to 5 μm long within the quartz veins, where it replaces native Dashuigou, Sichuan telluride deposit (Bi2Te2S: Bi: 58.31%, Te: 36.00%, gold, along with galena and chalcopyrite (Fig. 7b). S: 4.77%) (Mao et al., 1995a, 1995b). 28 S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34

Table 1 Electron microprobe analyses of telluride minerals from the Dongping gold deposit (wt.%).

Minerals Samples Se As Au Fe Cu Zn Ni Co Ag Pb Te Bi S Total Molecular formula

Calaverite DPA1798-2-1 0.24 0.00 42.07 0.46 0.00 0.00 0.07 0.00 0.62 0.00 56.92 0.72 0.06 101.14 Au0.97Te2.03

DPA1798-2-2 0.25 0.00 41.81 0.30 0.07 0.01 0.00 0.01 0.66 0.00 56.70 0.74 0.06 100.60 Au0.97Te2.03

DPB1333-1 0.32 0.00 40.62 0.43 0.05 0.00 0.01 0.01 0.69 0.00 56.74 0.69 0.07 99.63 Au0.95Te2.05

DPB21-115-1 0.31 0.00 40.88 0.03 0.33 0.01 0.00 0.00 0.41 0.00 57.45 0.57 0.00 99.99 Au0.95Te2.05

DPC4-137-7 0.29 0.00 41.78 0.45 0.00 0.10 0.00 0.00 0.66 0.00 55.34 0.29 0.04 98.95 Au0.99Te2.01

DPC4-137-10 0.28 0.00 41.00 0.59 0.41 0.00 0.02 0.02 1.54 0.00 55.71 0.49 0.29 100.36 Au0.97Te2.03

Petzite DPA1798-2-2-2 0.10 0.00 24.39 2.74 0.01 0.00 0.01 0.00 40.84 0.00 31.86 0.28 1.36 101.60 Ag3.02Au0.99Te1.99

DPB1333-4 0.13 0.00 24.76 0.61 0.03 0.00 0.01 0.00 42.95 0.00 30.30 0.09 0.11 98.99 Ag3.14Au0.99Te1.87

DPB1950-2-1 0.18 0.00 23.55 0.16 0.06 0.04 0.01 0.02 42.57 0.00 33.63 0.34 0.17 100.73 Ag3.04Au0.92Te2.03

DPC4-137-1 0.08 0.00 24.36 0.21 0.13 0.00 0.02 0.01 43.02 0.00 33.10 0.19 0.10 101.22 Ag3.06Au0.95Te1.99

DPC4-137-8 0.00 0.00 24.01 0.55 0.00 0.00 0.00 0.00 42.09 0.00 33.88 0.35 0.14 101.02 Ag3.01Au0.94Te2.05

Altaite DPB1333-2 0.00 0.00 0.00 0.53 0.07 0.00 0.00 0.01 0.19 59.90 37.88 0.00 0.05 98.63 Pb0.99Te1.17

DPB1950-1-1 0.19 0.00 0.00 0.77 0.00 0.04 0.00 0.01 0.18 59.87 37.51 0.00 0.11 98.67 Pb0.99Te1.17

DPB1950-2-2-1 0.12 0.00 0.00 0.36 0.02 0.08 0.01 0.03 0.24 60.33 37.26 0.00 0.04 98.48 Pb1.00Te1.17

DPB21-115-4 0.12 0.00 0.06 0.03 0.00 0.00 0.00 0.00 0.23 60.23 38.18 0.00 0.00 98.84 Pb0.99Te1.18

DPB5234-16 0.15 0.00 0.00 0.06 0.00 0.02 0.00 0.00 0.00 0.00 48.30 52.69 0.00 101.21 Bi2.00Te3.00

Tellurobismuthit DPB5234-17 0.15 0.00 0.00 0.05 0.00 0.02 0.01 0.00 0.04 0.00 48.69 51.91 0.00 100.86 Bi1.97Te3.03

DPB5234-18 0.30 0.00 0.05 0.03 0.00 0.02 0.01 0.02 0.04 0.00 48.32 52.85 0.01 101.63 Bi2.00Te3.00

DPB5234-19 0.22 0.00 0.00 0.23 0.00 0.00 0.00 0.03 0.06 0.00 46.58 54.33 0.27 101.71 Bi2.08e2.92

DPB5234-4 0.22 0.00 0.00 0.18 0.01 0.01 0.00 0.00 0.02 0.00 36.26 58.34 4.64 99.69 Bi1.97Te2.02S1.02

DPB5234-5 0.13 0.00 0.00 0.02 0.02 0.00 0.01 0.00 0.05 0.00 37.00 59.31 4.40 100.93 Bi2.00Te2.04S0.97

DPB5234-2 0.23 0.00 0.10 0.10 0.00 0.03 0.00 0.03 0.03 0.00 36.41 59.18 4.37 100.47 Bi2.01Te2.02S0.97

Tetradymite DPB5234-12 0.21 0.00 0.02 0.08 0.03 0.00 0.01 0.00 0.00 0.00 36.52 59.72 4.49 101.07 Bi2.01Te2.01S0.98

DPB5234-13 0.26 0.00 0.00 0.10 0.00 0.01 0.01 0.00 0.00 0.00 36.83 58.56 4.57 100.34 Bi1.97Te2.03S1.00

DPB5234-14 0.09 0.00 0.00 0.19 0.02 0.00 0.00 0.00 0.02 0.00 36.44 60.93 3.54 101.23 Bi2.12Te2.08S0.80

DPB5234-20 0.25 0.00 0.01 0.06 0.00 0.00 0.01 0.02 0.01 0.00 37.50 59.66 3.34 100.85 Bi2.09Te2.15S0.76

DPB5234-21 0.25 0.00 0.08 0.04 0.04 0.00 0.00 0.02 0.05 0.00 37.24 59.28 3.44 100.43 Bi2.08Te2.14S0.79

Table 2 Electron microprobe analyses of native gold from the Dongping gold deposit (wt.%).

Samples Se As Au Fe Cu Zn Ni Co Ag Pb Te Sb Bi S Total Au ﬁneness Molecular formula

DPA1956-2-1 0.02 0.04 94.50 0.54 0.08 0.02 0.00 0.01 4.81 0.00 0.02 0.00 1.18 0.05 101.25 952 Au0.92Ag0.08

DPB5234-1 0.00 0.00 92.85 0.02 0.00 0.01 0.00 0.00 4.78 0.00 0.00 0.00 0.69 0.00 98.34 951 Au0.91Ag0.09

DPB5234-3 0.02 0.00 93.48 0.23 0.03 0.03 0.00 0.00 4.91 0.00 0.23 0.00 1.23 0.01 100.18 950 Au0.91Ag0.09

DPB985-1-2 0.00 0.00 90.64 0.37 0.07 0.00 0.00 0.00 5.37 0.00 0.00 0.00 1.44 0.21 98.11 944 Au0.90Ag0.10

DPB1333-3 0.02 0.00 89.60 1.40 0.00 0.02 0.00 0.02 6.56 0.00 0.03 0.00 0.44 0.16 98.24 932 Au0.88Ag0.12

DPB15Q3-1-1 0.00 0.00 89.80 0.09 0.04 0.02 0.01 0.00 6.78 0.00 0.00 0.00 1.28 0.13 98.14 930 Au0.88Ag0.12

DPB1950-1-2 0.00 0.00 91.07 0.52 0.00 0.00 0.00 0.00 6.10 0.00 0.00 0.00 1.34 0.21 99.24 937 Au0.89Ag0.11

DPB1950-2-2-3 0.03 0.00 92.62 0.90 0.10 0.00 0.01 0.00 6.07 0.00 0.03 0.00 1.29 0.08 101.12 938 Au0.89Ag0.11

DPB21-115-2 0.00 0.00 93.39 0.01 0.00 0.00 0.01 0.00 6.27 0.00 0.08 0.00 1.76 0.00 101.52 937 Au0.89Ag0.11

DPC4-137-2 0.00 0.03 89.13 1.18 0.00 0.00 0.06 0.00 5.85 0.00 0.07 0.00 0.98 0.72 98.02 938 Au0.89Ag0.11

DPC4-137-9 0.03 0.00 93.43 0.20 0.00 0.00 0.02 0.00 5.99 0.00 0.00 0.00 1.36 0.09 101.11 940 Au0.90Ag0.10

DPC1364S-1-2 0.03 0.00 90.39 0.03 0.01 0.05 0.00 0.03 7.12 0.00 0.04 0.00 1.35 0.03 99.08 927 Au0.87Ag0.13

4.2. The native gold (Fig. 8b),which is the most common occurrence of native gold in the deposit; and (iv) grains coexisting with calaverite, altaite, petzite Native gold in the ores occurs in varieties of forms: (i) blebs enclosed (Fig. 8c), which in places may be accompanied by sulﬁdes such as in quartz, common in the auriferous quartz veins (Fig. 8a); (ii) bladed chalcopyrite, galena and sphalerite. The morphology of the minerals grains coexisting with magnetite and hematite (Fig. 8d); (iii) irregular suggests equilibrium among the native gold, tellurides, pyrite and grains ﬁlling fractures in pyrite or along the rims of pyrite and quartz quartz which is typical of the mineralization stage III.

Table 3 X-ray powder diffractograms of telluride minerals and native gold from Dongping gold deposit.

Samples

DPA1798 DPB1950 DPC4137-2a DPC4137-2c DPB5234a DPB5234b

d(Å) I%d(Å)I%d(Å)I% d (Å) I% d (Å) I% d (Å) I%

2.11 100 1.32 100 1.47 100 3.02 100 2.32 100 3.22 100 3.02 42 2.12 94 2.94 65 1.32 92 1.44 18.5 2.19 35.54 1.32 36 2.10 82 2.11 57 2.28 78 2.04 16.7 2.37 32.64 1.70 33 2.04 76 1.95 13 2.11 75 1.23 15.8 1.61 29.97 1.34 33 2.78 70 1.32 13 2.35 35 2.12 7.87 1.40 15.61 2.29 22 2.07 52 1.76 10 2.04 32 2.10 4.58 1.49 15.47 2.35 21 2.32 49 1.80 8 1.07 31 0.93 4.42 1.30 11.04 3.23 16 3.02 36 1.70 8 1.86 30 0.91 4.39 2.35 10.16 S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34 29

Fig. 7. Reﬂected light photomicrographs of Te–S–Bi tellurides from the Dongping gold deposit, (a)—tellurobismuthite replacing native gold. (b)—Galena and tetradymite replacing native gold. Ttd—Tetradymite. Tel—Telluriobismuthite. Gn—Galena. Mag—Magnenite. Hem—Hematite.

The grain size of native gold varies from 5 to 350 μm, mostly 10– for this stage include pyrite–chalcopyrite–altaite–petzite–calaverite– 30 μm. In a very small amount of hand specimens the native gold is native gold and magnetite–hematite–native gold–tellurobismuthite– visible under naked eyes, with an average ﬁneness of 940 (Table 2). tetradymite associations. The textures of the ores suggest that the native gold and Au–Ag–Pb tellurides precipitated simultaneously (Fig. 8c). 5. Discussion Bismuth-bearing tellurides intergrown with magnetite and hematite, also suggest a coexisting relationship. 5.1. Mineral paragenesis The paragenetic sequence of the main minerals, supported by textural evidence, could be summarized as: pyrite → chalcopyrite → altaite → Compositions of tellurides and native gold are plotted on the Au– petzite → calaverite → native gold (Fig. 6, Fig. 7). Ag–Te and Bi–S–Te ternary diagrams (Fig. 10). The Au– and Ag– With reference to the paragenetic association and ore-forming tem- tellurides fall in between the Au–AuTe2 and AuTe2–Ag3AuTe2 end mem- perature, it is inferred that the pyrite, chalcopyrite and galena began to bers. The calaverite is relatively Au-rich and Petzite is relatively Au- and precipitate from ore-forming ﬂuids at high temperature (300–400 °C),

Te-rich. The Bi–S tellurides fall in between Bi2Te3–Bi2Te2S end members which consumed substantial amount of Fe and S. With the decrease of and are mostly close to the standards except for lower S in a few temperature, sulfur fugacity gradually declined, matched by relative in- analyses. crease of tellurium fugacity. The precipitation of tellurides started along The tellurides formed mostly in the polymetallic sulﬁde–quartz stage, with the formation of a small amount of sulﬁdes and native gold, the principal mineralization stage. The dominant mineralogy typical resulting in chalcopyrite–altaite–native gold association. The lowering

Fig. 8. Reﬂected light photomicrographs of the native gold from the Dongping gold deposit, (a)—native gold hosted in quartz. (b)—Native gold hosted in crack and edge of pyrite. (c)—Coexistence of native gold with tellurides. (d)—Native gold in intergranular crack of magnenite. Au—Native gold. Cav—Calaverite. Ptz—Petzite. Alt—Altaite. Py—pyrite. Mag—Magnenite. Hem—Hematite. Qz—Quartz. 30 S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34

Fig. 9. X–ray powder diffractograms of tellurides and native gold from the Dongping gold deposit.

of temperature was matched by increasing fTe2/fS2, and the resultant The tellurides in general formed later than the sulfides in the gold–silver tellurides are composed of chalcopyrite–altaite–petzite– Dongping deposit. The precipitation sequence for the tellurides is as calaverite–native gold. Finally, both sulfur fugacity and tellurium fugac- follows: altaite–petzite–calaverite. This indicates that Te first combined ity decreased, and Te incorporated residual Au and Ag to form tellurides, with Pb to form altaite first, and then combined with Au and Ag to form giving rise to the formation of petzite, calaverite and native gold petzite. Finally, the residual Te incorporated with Au to form calaverite, association. which was associated by the precipitation of a small amount of native S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34 31

Fig. 10. The Au–Ag–Te and Bi–Te–S ternary system and its mineral paragenesis. (After Cabri, 1965; Markham, 1960). gold. The sulfur- and bismuth-bearing tellurides formed later than the the telluride enrichment and native gold fineness, suggesting gold magnetite, hematite and native gold (Fig. 7a, b). enrichment was coupled with telluride precipitation. The tellurides in the southern ore bodies are more abundant than the north, which 5.2. The spatial distribution of minerals mainly consist of altaite, petzite and calaverite coexisting with pyrite and chalcopyrite. Vertically, the quantities and species of tellurides and native gold in Whole rock geochemistry demonstrates that As, Sb, Hg, Au, Ag, Te, the ore bodies decrease downward gradually, along with decline of Pb, Zn and W are enriched in the south-central of the deposit, and the native gold finesse (Fig. 11a), indicating that the lower part of ore bodies Au–Ag–Te anomalies overlap Cu–Pb–Zn anomalies. Bi displays a contains less tellurides than the upper, and with increasing depth more positive anomaly in the north. These geochemical trends are compatible gold was substituted by Ag in the native gold via isomorphism. with the mineralogical zoning in the ore bodies (Fig. 12). Krennerite, hessite, stutzite and oxygenated tellurate have been published previously for the upper part of ore bodies (Song and Zhao, 1996; Zhang et al., 2002)(Table 4). As this study is directed to the 5.3. The physical–chemical conditions for telluride precipitation lower part of ore bodies, it is inferred that the absence of krennerite, hessite and stutzite might be due to the vertical variation. An exception Tellurium is a dispersed element in the crust, and telluride precipita- is that tetradymite is identified in the lower part of deposit. tion requires high tellurium fugacity and low sulfur fugacity. The Horizontally, mineralogy in the northern portion of the deposit is Dongping gold deposit formed in a sulfur-poor and tellurium-rich characterized by native gold, magnetite and hematite, the middle environment (Song and Zhao, 1996), which is supported by the nega- portion of the deposit is dominated by native gold and pyrite, whereas tive correlation between sulfides and tellurides in the deposit. In the southern portion is marked by native gold and tellurides. The fine- quartz–polymetallic sulfide–telluride–gold stage, the tellurides ness of native gold decreases gradually southwards, and then increases postdate sulfides, indicating that the telluride precipitated in a sulfur- upward (Fig. 11b), which could be accounted for by telluride enrich- depleted environment, (Tu et al., 2004), as a result of sulfide ment in the south. The native gold intergrown with oxide minerals precipitation. demonstrates the highest finesse, whereas those in pyrite fractures The stability diagram of Au–Ag–Te minerals indicates stable temper- and voids exhibit low fineness. There is a positive correlation between ature for gold and silver tellurides at 145 °C to 313 °C (Fig. 13). The

Fig. 11. Space variation relationship of fineness of native gold from the Dongping gold deposit, (a)—vertical variation of average fineness of native gold (elevation N 1400 m after Song and Zhao, 1996). (b)—Lateral variation of average fineness of native gold. 32 S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34

Table 4 Ore minerals from Dongping gold deposit.

Types Position Main ore minerals Telluride minerals Date

Quartz vien Orebody 1 Pyrite, galena, magnetite, chalcopyrite, Calaverite, petzite, altaite, hessite, krennerite, stutzite, Song and Zhao (1996); sphalerite and native gold Pb-bearing native tellurium and oxygenated tellurate Zhang et al. (2002) Alterated rocks Orebody 70 Pyrite, magnetite, chalcopyrite, shalerite Calaverite, petzite, altaite, tellurobismuthite and tetradymite This study and native gold

paragenetic association of minerals from Dongping gold deposit may petzite, calaverite, native gold and minor chalcopyrite were precip- imply the following reactions for formation of the tellurides: itated. The absence of hessite in the lower ore body suggests low silver fugacity.

4Ag + Te2(g)=2Ag2Te At lower temperature, sulfur fugacity and tellurium fugacity decrease. With reference to the telluride and sulﬁde stability diagram

(Aﬁﬁ et al, 1988), at 275 °C, log ƒ (S2) varies from −13.50 to −11.62 Au + Te2 = AuTe2 and log ƒ (Te2)from−10.69 to −9.05 (Fig. 14). The geochemistry of the deposit, high Au, Te, Pb and Bi concentra-

3Ag2Te + 2Au + 1/2Te2(g)=2AuAg3Te2 tions in the region favored precipitation of tellurides and native gold, resulting in abundant calaverite, altaite, petzite, tellurobismuthite and tetradymite. 2PbS + Te2(g)=2PbTe+S2 6. Conclusions Pb + 0.5Te2(g)= PbTe The principal mineralogy of the ores in Dongping gold deposit is Taking account of the Ag content in native gold coexisting with the dominated by pyrite–chalcopyrite–altaite–petzite–calaverite–native tellurides, and the correlation between Ag content and temperature, gold. The species and content of tellurides decrease from the upper to Au–Ag 0 i.e., μAg = μAg + RTlnNAg − [5650 − 1600 (1 − NAg) − 1.375 T] the lower sectors of the ore bodies, which are positively correlated 2 (1 − NAg) (White et al., 1957), it is calculated that log f (Te2) varied with the native gold fineness. Laterally, telluride species and content from −8.650 to − 7.625 at 300 °C which is consistent with fluid as well as native gold finesse exhibit significant variations. Regional geo- inclusion homogenization temperature ranging between 270 and chemical anomalies are consistent with the mineralogical variations. 330 °C (Gao, unpublished data). During the telluride and gold precipitation process, Te preferentially With reference to the mineral paragenesis of pyrite–altaite–petzite– incorporated Pb to precipitate altaite, which was followed by the incor- calaverite–native gold and the stability diagram for tellurides and poration of Au and Ag to form abundant petzite. When Ag was sulfides at 300 °C (Afifi et al., 1988), log ƒ (S2) for the principal telluride consumed substantially, Te incorporated Au to form calaverite. Finally, precipitation stage could be constrained in the range of −9.12 to −6.43 Te was depleted by precipitation of tellurides, which lead to the precip- and log ƒ (Te2)from−11.47 to −8.86. In this stage, pyrite, altaite, itation of the residual Au, Ag and formation of native gold.

Fig. 12. Spatial distribution of the minerals. S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34 33

Fig. 13. Stability diagram of Au–Ag–Te minerals. (After Bortnikov et al., 1988).

The tellurides precipitated mostly at around 300 °C, with log f (Te2) References ranging between −9.12 and −6.43 and log ƒ (S2) between −11.47 and −8.86. The high Au, Te, Pb and Bi concentration in the region provided Afifi, A.M., Kelly, W.C., Esscue, E.J., 1988. Phase relations among tellurides, sulfides, and oxides: I. Thermochemical date and calculated equilibria. Econ. Geol. 83, 377–394. favorable geochemical background for the ore genesis. High Te fugacity Bao, Z.W., Zhao, Z.H., 2006. Isotopic geochemical constrains on metallogeny of the and the ore-forming element enrichments favored the precipitation of Dongping-type gold deposits associated with syenites. Acta Petrol. Sin. 22 (10), tellurides, resulting in high gold finesse. 2534–2542 (in Chinese with English abstract). Bortnikov, N.S., Kramer, K., Genkin, A.D., Krapivaa, L.Y., Santa Cruza, M., 1988. Parageneses of gold and silver tellurides at the Florencia gold deposit, Cuba. Geol. Rudn. Mest. 2, 49–61. Acknowledgments Cabri, L.J., 1965. PhaserelationsintheAu–Ag–Te system and their mineralogical significance. Econ. Geol. 60 (8), 1569–1606. Fan, H.R., Xie, Y.H., Zhai, M.G., 2001. Study of ore-forming fluids in the Dongping gold deposit, The Chongli Zijin Mining Group Co., Ltd provided enormous support – fi North-Western Hebei. Sci. China Ser. D Earth Sci. 31 (7), 538 544 (in Chinese). for the eld work. Mr Chen Zhenyu from the Institute of Mineral Re- Fang, Y.K., Shuai, D.Q., 1988. The first discovery of the Au–Te telluride minerals sources Chinese Academy of Geological Sciences helped in the electron of Yangzaiyu gold deposit of Henan province. Acta Petrol. Mineral. 8 (4), 20–26 probe analysis. Professor Gu Xiangping from Central South University (in Chinese with English abstract). Hu, W.X., Sun, G.X., Zhan, W.L., Wang, Z.K., 2005. Au–Ag telluride minerals and their provided very helpful guide in the XRD analysis, and valuable sugges- precipitation mechanism in the Rushan gold deposit, Shandong. Acta Mineral. Sin. tions for revision of the manuscripts. These are all gratefully recognized. 25 (2), 177–182 (in Chinese with English abstract).

Fig. 14. Stabilities of sulfides and tellurides as a function of f (S2)andf (Te2)(afterAfifi et al., 1988), (a)—Minerals at 300. (b)—Minerals at 200. 34 S. Gao et al. / Ore Geology Reviews 64 (2014) 23–34

Li, C.M., Deng, J.F., Su, S.G., Li, H.M., Liu, X.M., 2010. Two stage zircon U–Pb ages of the Wang, P., 1987. Systematic Mineralogy. Geological Publishing House, Bejing, pp. 231–501 potash altered rock in the Dongping gold deposit, Hebei Province, and their geologi- (in Chinese). cal implications. Acta Geosci. Sin. 31 (6), 843–852 (in Chinese with English abstract). White, J.L., Orr, R.L., Hultgren, R., 1957. The thermodynamic properties of silver–gold Liu, J.L., Bai, X.D., Zhao, S.J., Tran, M.D., Zhang, Z.C., Zhao, Z.D., Zhao, H.B., Lu, J., 2011. alloys. Acta Metall. 5 (12), 747–760. Geology of the Sandaowanzi telluride gold deposit of the northern Great Xing'an Xu, H., Yu, Y.X., Gao, S., Tian, Z., Wu, X.K., Yang, L.J., Wang, Q.S., Sun, Y., 2011. A new Range, NE China: geochronology and tectonic controls. J. Asian Earth Sci. 41 (2), 107–118. crystalline compounds of Au–Te in Sandaowanzi gold deposit, Heilongjiang Province. Mao, J.W., Chen, Y.C., Wang, P.A., 1995a. Geology and geochemistry of the Dashuigou Geol. Bull. China 30 (11), 1779–1784 (in Chinese with English abstract). tellurium deposit, Western Sichuan, China. Int. Geol. Rev. 37, 526–546 (in Chinese Xu, H., Yu, Y.X., Wu, X.K., Yang, L.J., Tian, Z., Gao, S., Wang, Q.S., 2012. Intergrowth texture with English abstract). in Au–Ag–Te minerals from Sandaowanzi gold deposit, Heilongjiang Province: Mao, J.W., Chen, Y.C., Yang, B.C., Lei, Y.F., Zhou, J.X., 1995b. Tetradymite from the implication for ore-forming environment. 57 (1), 1–9. Dashuigou tellurium deposit, Sichuan, Southwest, China. Sci. Geol. Sin. 30 (1), Yu, Y.X., Xu, H., Wu, X.K., Yang, L.J., Tian, Z., Gao, S., Wang, Q.S., 2012. Characteristics of 47–52 (in Chinese with English abstract). the Au–Ag–Te minerals and its ore-forming fluids in Sandaowanzi gold deposit, Markham, N.L., 1960. Synthetic and natural phases in the system Au–Ag–Te. Econ. Geol. Heilongjiang Province. Acta Petrol. Sin. 28 (01), 345–356 (in Chinese with English 55 (6), 1148–1178. abstract). Nie, F.J., Jiang, S.H., Liu, Y., 2004. Intrusion-related gold deposit of North China Craton, Zhang, Z.C., 1996. Characteristics of H and O isotopes and fluid evolution in Dongping gold People's Republic of China. Resour. Geol. 54, 299–324. deposit. Gold Geol. 2 (3), 36–41 (in Chinese with English abstract). Pals, D.W., Spry, P.G., 2003. Telluride mineralogy of the low-sulfidation epithermal Zhang, P.H., Zhao, Z.H., Zhu, J.C., Zhang, W.L., Bao, Z.W., Zhang, Y.H., 2002. Tellurides of Emperor gold deposit, Vatukoula, Fiji. Miner. Petrol. 79, 285–307. gold and silver and their capacity of carrying gold in ores from the Dongping-type Song, G.R., Zhao, Z.H., 1996. Geology of Dongping alkaline complex-hosted gold deposit in gold deposits, Hebei province, China. Acta Mineral. Sin. 22 (4), 321–328 (in Chinese Hebei Province. Seismological Press, Beijing, pp. 4–109 (in Chinese). with English abstract). Thompson, T.B., Trippel, A.D., Dwelley, P.C., 1985. Mineralized veins and breccias of the Zhang, G.R., Xu, J.H., Wei, H., Song, G.C., Zhang, Y.B., Zhao, J.K., He, B., Chen, D.L., 2012. Cripple Creek district, Colorado. Econ. Geol. 80, 1669–1688. Structure, alteration, and fluid inclusion study on deep and surrounding area of Tu, G.C., Gao, Z.M., Hu, R.Z., Zhang, Q., Li, Z.Y., Zhao, Z.H., Zhang, B.G., 2004. Geochemistry the Dongping gold deposit, northern Hebei, China. Acta Petrol. Sin. 28 (2), 637–651 and Metallogenic Mechanism of Dispersed Elements. Geological Publishing House, (in Chinese with English abstract). Bejing, pp. 268–317 (in Chinese with English abstract). Zhao, S.J., Liu, J.L., Bai, X.D., Zhao, H.B., Lv, J., Chen, Y., Tran, M.D., 2010. Fluid inclusions and Wallier, S., Rey, R., Kouzmanov, K., Heinrich, C.A., Leary, S., O'Connor, G., Tamas, C., sulfur isotopes of Sandaowanzi gold telluride deposit, Heilongjiang Province. Miner. Vennemann, T., Ullrich, T., 2006. Magmatic fluids in the breccias-hosted epithermal Depos. 29 (3), 476–488 (in Chinese with English abstract). Au–Ag deposit of Rosia Montana, Romania. Econ. Geol. 101, 923–954. Zijin Mining in Chongli, 2011. Unpublished mining report.