Mineralization, ore mineral chemistry and sulfur stable isotopes at the Chaldaq gold prospect (north Takab): evidence for gold formation mechanism

Document Type : Research Article

Authors

• Roya Bigdeli
• Ebrahim Tale Fazel
• Mohammad Maanijou

Department of Geology, Faculty of Basic Sceinces, Bu-Ali Sina University, Hamedan, Iran

10.22067/econg.v13i1.83781

Abstract

Introduction
The Takab-Angouran ore field, one of the Iran’s largest gold districts, is located in northwestern Zagros and belongs to the northwestern part of the Sanandaj-Sirjan Zone. This area has a dominant NW-SE structural trend and is spatially associated with the Sanandaj-Sirjan zone. Its geological and petrological characteristics seem to have closer affinities to the Central Iran zone. There are no chronological data on the ultramafic rocks or associated amphibolites, granulites and calc-silicates of the Takab area and the petrogenesis of the ultramafic rocks and their tectonic relations with other parts of the metamorphic complex are unclear. A Neoproterozoic-Lower Cambrian age for the protoliths of Takab-Angouran ore field seems likely, in view of comparable lithology, stratigraphy and geochronology with the Central Iran zone.
The Chaldaq gold prospect is located in the Takab-Angouran ore field, NW Iran, within Iman Khan NW-trending anticline. The rock units at the mining area mainly consist of Precambrian sequence (Iman Khan schist, Chaldaq limestone and Zarshuran black shale) overlain by Cambro-Ordovician limestone and Oligo-Miocene Qom Formations (Mehrabi et al., 1999). The gold mineralization in the Chaldaq prospect is hosted by Chaldaq carbonaceous sedimentary rocks. Two major sets of faults which were recognized by Mehrabi et al., 1999 at the Zarshuran mine are: 1) northwest (310–325) and 2) southwest (255–265). Herein, we report on the textural, paragenetic relationships, mineral chemistry and sulfur isotopes of the Chaldaq prospect. This study is focused on: (1) documenting the chemical composition of different sulfides, (2) determining the chemical state of gold in iron sulfides, (3) determining the sulfur activity, and (4) source of sulfur.
 
Materials and methods
About 70 rock samples were collected from various parts of the deposit for determinations of mineralogy, mineral texture, mineral chemistry and sulfur isotope. The polished thin sections were carbon coated and analyzed on a Camera SX100 electron microprobe at the Iranian Mineral Processing Research Center (IMPRC), Karaj. The detection limits for major and minor elements are approximately 0.05 and 0.01 wt.%, respectively. Sulfur isotope analyses were conducted on 0.05 g of a 200-mesh sized of pyrite and realgar which were handpicked and checked under a binocular microscope to ensure purity of >98%. Each sample was reacted with Cu₂O powder to produce SO₂. The SO₂ gas was collected and purified, and followed by S isotopic analysis using a MAT252 mass spectrometer at stable isotope laboratory of the University of Arizona. The δ³⁴S values were reported relative to Vienna Cañon Diablo Troilite (VCDT), and analytical precision is ±0.2‰.
 
Results and discussion
Based on field and petrographic observations, three mineralization stages including diagenetic, hydrothermal (early-ore, main-ore and late-ore substages), and supergene stages were identified at the Chaldaq deposit. At least six types of pyrite and arsenian pyrite were recognized at the Chaldaq deposit. On the basis of EPMA results, gold with 10 to 80 ppm Au content occurs as solid solution (Au⁺)in arsenian pyrite [(Fe²⁺As³⁺)S₂Au₂.S⁰]. Various studies have documented that gold in the primary ores of sediment-hosted gold deposits is largely hosted by arsenian pyrite, and that gold in occurs as a substituting cation in the form of  solid solution (Au⁺) and/or as nanoparticles of native gold (Au⁰) (Cook and Chryssoulis, 1990; Fleet and Mumin, 1997; Reich et al., 2005). Au^– and Au³⁺ have also been suggested to occur as solid solution in pyrite (Arehart et al., 1993; Li et al., 2003). The understanding of the chemical state of gold in iron sulfides is important for deep understanding of gold depositional mechanism in sediment-hosted gold deposits. Main-ore substage sulfide minerals has δ³⁴S values ranging from 3.5 to 6.5 ‰ (avg. 5‰, n=6). The Fe content of sphalerites from the main-ore indicates that sphalerite precipitated from relatively low fS₂ fluid. Based on all evidence, it can be said that sulfur mineralization of the Chaldaq prospect has been formed by the performance of oxidized hydrothermal fluid on organic-bearing carbonaceous host rocks (at the Chaldaq unit) and the systematic subtraction of H₂S reductive species from that environment. Considering the low temperature (fS₂ between -14 to -16) and the acidic to neutral pH (presence of kaolinite and illite) for the main-ore stage of hydrothermal mineralization in the Chaldaq prospect, probably the major contribution of sulfur is in the form of H₂S.
References
Arehart, G.B., Chryssoulis S.L. and Kesler, S.E., 1993. Gold and arsenic in iron sulfides from sediment-hosted disseminated gold deposits: implications for depositional processes. Economic Geology, 88(3): 171–185. https://doi.org/10.2113/gsecongeo.88.1.171
Cook, N.J. and Chryssoulis S.L., 1990. Concentrations of invisible gold in the common sulfides. Canadian Mineralogist, 28(3): 1–16. https://doi.org/10.1007/s00126-0140562-z
Fleet, M.E. and Mumin, A.H., 1997. Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin trend gold deposits to laboratory synthesis. American Mineralogist, 82(3): 182–193. https://doi.org/10.2138/am-1997-1-220
Li, J.L., Qi, F. and Xu, Q.S., 2003. A negatively charged species of gold in minerals–further study of chemically bound gold in arsenopyrite and arsenian pyrite. Neues Jahrbuch für Mineralogie-Abhandlungen, 5(2): 193–214. https://doi.org/10.1127/0028-3649/2003/2003-0193
Mehrabi, B., Yardley, B.W.D. and Cann, J.R., 1999. Sediment-hosted, disseminated gold mineralisation at Zarshuran, NW Iran. Mineralium Deposita, 34(3): 656–671. https://doi.org/10.1007/s001260050227
Reich, M., Kesler, S.E., Utsunomiya, S., Palenik, C.S., Chryssoulis, S.L. and Ewing, R.C., 2005. Solubility of gold in arsenian pyrite. Geochimica and Cosmochimica Acta, 69(6): 2781–2796. https://doi.org/10.1016/j.gca.2005.01.011

Keywords

• Arsenian pyrite
• Ore mineral chemistry
• Sulfur isotope
• Gold
• Chaldaq prospect
• Zarshuran

20.1001.1.20087306.1400.13.1.4.8

---

References

Asadi, H.H., Voncken, J.H.L., Kuhnel, R.A. and Hale, M., 2000. Petrography, mineralogy and geochemistry of Zarshuran Carlin-like gold deposit, northwest Iran. Mineralium Deposita, 35(3): 656–671. https://doi.org/10.1007/s001260050269

Arehart, G.B., Chryssoulis S.L. and Kesler, S.E., 1993. Gold and arsenic in iron sulfides from sediment-hosted disseminated gold deposits: implications for depositional processes. Economic Geology, 88(3): 171–185. https://doi.org/10.2113/gsecongeo.88.1.171

Arehart, G.B. and Donelick, R.A., 2006. Thermal and isotopic profiling of the Pipeline hydrothermal system: Application to exploration for Carlin-type gold deposits. Journal of Geochemical Exploration, 91(2): 27–40. https://doi.org/10.1016/j.gexplo.2005.12.005

Babakhani, A. and Ghalamghash, J., 1998. Geological map of Takht-e-Soleyman, scale 1:100,000. Geological Survey of Iran.

Bakken, B.M., Hochella, M.F., Marshall, A.F. and Turner, A.M., 1989. High resolution microscopy of gold in unoxidized ore from the Carlin Mine, Nevada. Economic Geology, 84(5): 171–179. https://doi.org/10.1007/BF03220200

Barnes, H.L., 1997. Geochemistry of hydrothermal ore deposits. John Wiley, New York, 797 pp.

Berglund, S. and Ekstrom, T.K., 1980. Sphalerite composition in relation to the stress distribution of a boudinage. Lithos, 7(4): 1–6. https://doi.org/10.1016/0024-4937(74)90031-0

Bigdeli, R., 2019. Mineralogy, geochemistry and genesis of the Chaldagh gold index in north of Zarshuran deposit, northern Takab. M.Sc. Thesis, Bu-Ali Sina University, Hamedan, Iran, 194 pp.

Blanchard, M., Alfredsson M., Brodholt, J., Wright, K. and Catlow, C.R.A., 2007. Arsenic incorporation into FeS₂ pyrite and its influence on dissolution: a DFT study. Geochimica and Cosmochimica Acta, 71(3): 624–630. https://doi.org/10.1016/j.gca.2006.09.021

Carrillo-Rosúa, J., Morales-Ruano, S., Morata, D., Boyce, A.J., Belmar, M., Fallick, A.E. and Hach-Alí, P.F., 2008. Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile. Mineralogy and Petrology, 92(5): 341–360. https://doi.org/10.1007/s00710-007-0203-7

Cook, N.J. and Chryssoulis S.L., 1990. Concentrations of invisible gold in the common sulfides. Canadian Mineralogist, 28(3): 1–16. https://doi.org/10.1007/s00126-0140562-z

Cline, J.S., Hofstra, A., Munteau, J., Tosdal, D. and Hickey, K., 2005. Carlin-type gold deposits in Nevada: Critical geologic characteristics and viable models. Economic Geology, 89(3): 451−484. https://doi.org/10.5382/AV100.15

Chang, Z., Large, R.R. and Maslennikov, V., 2008. Sulfur isotopes in sediment-hosted orogenic gold deposits: evidence for an early timing and a seawater sulfur source. Geology, 36(2): 971–974. https://doi.org/10.1130/G25001A.1

Czamanske, K.G., 1974. The FeS content of sphalerite along the chaqlcopyrite-pyrite-bornite sulfur fugasity buffer. Economic Geology, 68(4): 1328–1334. https://doi.org/10.2113/gsecongeo.69.8.1328

Daliran, F., 2008. The carbonate rock-hosted epithermal gold deposit of Agdarreh, Takab geothermal field, NW Iran–hydrothermal alteration and mineralization. Mineralium Deposita, 43(4): 383–404. https://doi.org/10.1007/s00126-007-0167-x

Deditius, A.P., Utsunomiya S., Renock, D., Ewing, R.C., Ramana, C.V., Becker, U. and Kesler, S.E., 2008. A proposed new type of arsenian pyrite: composition, nanostructure and geological significance. Geochimica and Cosmochimica Acta, 72(3): 2919–2933. https://doi.org/10.1016/j.gca.2008.03.014

Einaudi, M.T., Hedenquist, J.H. and Inan, E.E., 2003. Sulfidation state of fluids in active and extinct hydrothermal systems: transtions from porphyry to epithermal enviroments. In: S.F. Simmons and I.J. Graham (Editors), Volcanic, geothermal and ore-forming fluids: Rulers and witnesses of processes within the Earth. Society of Economic Geologists, New York, pp. 285–313. https://doi.org/10.5382/SP.10.15

Fleet, M.E. and Mumin, A.H., 1997. Gold-bearing arsenian pyrite and marcasite and arsenopyrite from Carlin trend gold deposits to laboratory synthesis. American Mineralogist, 82(3): 182–193. https://doi.org/10.2138/am-1997-1-220

Field, C.W. and Fifarek, R.H., 1985. Light stable isotope systematics in the epithermal environment. In: B.R. Berger and P.M. Bethke (Editors), Geology and geochemistry of epithermal systems. Reviews of Economic Geology, New York, pp. 99–128. https://doi.org/10.5382/Rev.02.06

George, L.L., Biagioni, C., D’Orazio, M. and Cook, N.J., 2018. Textural and trace element evolution of pyrite during greenschist facies metamorphic recrystallization in the southern Apuan Alps (Tuscany, Italy): influence on the formation of Tl-rich sulfosalt melt. Ore Geology Reviews, 102(3): 59–105. https://doi.org/10.1016/j.oregeorev.2018.08.032

Gilg, H.A., Boni, M., Balassone, G., Allen, C.R., Banks, D. and Moore, F., 2006. Marble-hosted sulfide ores in the Angouran Zn-(Pb–Ag) deposit, NW Iran: interaction of sedimentary brines with a metamorphic core complex. Mineralium Deposita, 41(4): 1–16. https://doi.org/10.1007/s00126-005-0035-5

Gottesmann, W. and Kampe, A., 2007. Zn/Cd ratios in calcsilicate-hosted sphalerite ores at Tumurtijn-ovoo, Mongola. Chemie der Erde, 67(5): 323–328. https://doi.org/10.1016/j.chemer.2007.01.002

Grammatikopoulos, T.A., Valeyev, O. and Roth, T., 2006. Compositional variation in Hg-bearing sphalerite from the polymetallic Eskay Creek deposit, British Columbia Canada. Chemi der Erde, 66(3): 307–314. https://doi.org/10.1016/j.chemer.2005.11.003

Grant, H.L.J., Hannington, M.D., Petersen, S., Frische, M. and Fuchs, S.H., 2018. Constraints on the behavior of trace elements in the actively forming TAG deposit, Mid-Atlantic Ridge, based on LA-ICP-MS analyses of pyrite. Chemical Geology, 498(4): 45–71. https://doi.org/10.1016/j.chemgeo.2018.08.019

Hamdi, B., 1995. Precambrian–Cambrian deposits in Iran. In: A. Hushmandzadeh (Editors), Treatise of the Geology of Iran. Geological Society of Iran, Tehran, pp. 20–30.

Hoefs, J., 2015, Stable isotope geochemistry. Springer, London 244 pp.

Hofstra, A.H. and Cline, J.S., 2000. Characteristics and models for Carlin-type gold deposits. Economic Geology, 13(3): 163–220. https://doi.org/10.5382/Rev.13.05

Holland, H.D. and Malinin, S.D., 1997. The solubility and occurrence of non-ore minerals. In: H.L. Barnes (Editor), Geochemistry of hydrothermal ore deposits. John Wiley, New York, pp. 461–508.

Jonasson, I.R.M. and Sangster, D.F., 1978. Zn/Cd ratios for sphalerites separated from some Canadian sulphide ore samples. Geological Survey of Canada, 78(3): 195–201. https://doi.org/10.1016/j.gsf.2021.101241

Kavoshgaran Consultant Engineering., 2013. Prospecting and exploration preliminary study of the peripheral Zarshuran gold mine. Iranian Mines and Mineral Industries Development and Renovation Organization, Tehran, Report 2, 499 pp.

Kusebauch, C., Gleeson, S.A. and Oelze, M., 2019a. Coupled partitioning of Au and As into pyrite controls formation of giant Au deposits. Science Advances, 5(1): 1–8. https://doi.org/10.1126/sciadv.aav5891

Kusebauch, C., Oelze, M. and Gleeson, S.A., 2019b. Partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement. Chemical Geology, 500(3): 136–147. https://doi.org/10.1016/j.chemgeo.2018.09.027

Li, J.L., Qi, F. and Xu, Q.S., 2003. A negatively charged species of gold in minerals–further study of chemically bound gold in arsenopyrite and arsenian pyrite. Neues Jahrbuch für Mineralogie-Abhandlungen, 5(2): 193–214. https://doi.org/10.1127/0028-3649/2003/2003-0193

Lusk, J. and Calder, B.O.E., 2004. The composition of sphalerite and associated sulfides in reactions of the Cu-Fe-Zn-S, Fe-Zn-S and Cu-Fe-S systems at 1 bar and temperatures between 250 and 535 ºC. Chemical Geology, 203(3): 319–345. https://doi.org/10.1016/j.chemgeo.2003.10.011

Mao, S.H., 1991. Occurrence and distribution of invisible gold in a Carlin-type gold deposit in China. American Mineralogist, 76(4):1964–1972. https://doi.org/10.1155/2017/2417209

Mehrabi, B., Yardley, B.W.D. and Cann, J.R., 1999. Sediment-hosted, disseminated gold mineralisation at Zarshuran, NW Iran. Mineralium Deposita, 34(3): 656–671. https://doi.org/10.1007/s001260050227

Moghaddasi, S.J., Ebrahimi, M. and Mohammadi, F., 2019. Mineralogy, geochemistry and genesis of Gozaldarreh iron deposit, southeast Zanjan. Journal of Economic Geology, 11 (1): 33–55. (in Persian with English abstract) https://doi.org/10.22067/econg.v12i3.79628

Muntean, J.L., Cline, J.S., Simon, A.C. and Longo, A.A., 2011. Magmatic–hydrothermal origin of Nevada’s Carlin-type gold deposits. Nature Geoscience, 4(6):122–127. https://doi.org/10.1038/ngeo1064

Nabavi, M.H., 1976. Glossary of geology of Iran. Geological survey of Iran, Tehran 109 pp.

Nafisi, R., Kouhestani, H., Mokhtari, M.A. and Sadeqhi, M., 2019. Geochemistry and tectonomagmatic setting of protolite rocks of meta-volcanics in the Halab metamorphic complex (SW Dandy, Zanjan Province). Journal of Economic Geology, 11 (2): 211–235. (in Persian with English abstract) https://doi.org/10.22067/econg.v11i2.68167

Ohmoto, H. and Goldhaber, M., 1997a. Sulfur and carbon isotopes. In: H.L. Barnes (Editor), Geochemistry of hydrothermal ore deposits. John Wiley, New York, pp. 517–611.

Ohmoto, H. and Rye, R.O., 1997b. Isotope of sulfur and carbon. In: H.L. Barnes (Editor), Geochemistry of hydrothermal ore deposits. John Wiley, New York, pp. 509–567.

Reich, M., Kesler, S.E., Utsunomiya, S., Palenik, C.S., Chryssoulis, S.L. and Ewing, R.C., 2005. Solubility of gold in arsenian pyrite. Geochimica and Cosmochimica Acta, 69(6): 2781–2796. https://doi.org/10.1016/j.gca.2005.01.011

Scott, S.D., 1983. Chemical behaviour of sphalerite and arsenopyrite in hydrothermal and metamorphic environments. Mineralogical Magazine, 47(5): 427–435. https://doi.org/10.1180/minmag.1983.047. 345.03

Su, W.C., Zhang, H.T., Hu, R.Z., Ge, X., Xia, B., Chen, Y.Y. and Zhu, C., 2011. Mineralogy and geochemistry of gold-bearing arsenian pyrite from the Shuiyindong Carlin-type gold deposit, Guizhou, China: Implications for gold depositional processes. Mineralium Deposita, 47(3): 653–662. https://doi.org/10.1007/s00126-011-0328-9

Simon, G., Kesler, S.E. and Chryssoulis, S., 1999a. Geochemistry andtextures of gold-bearing arsenian pyrite, Twin Creeks, Nevada: implications for deposition of gold in Carlin-type deposits. Economic Geology, 94(4): 405–422. https://doi.org/10.2113/gsecongeo.94.3.405

Simon, G., Huang, H., Penner-Hahn, J.E., Kesler, S.E. and Kao, L., 1999b. Oxidation state of gold and arsenic in gold-bearing arsenian pyrite. American Mineralogist, 84(5): 1071–1079. https://doi.org/10.2138/am-1999-7-809

Stöcklin, J., 1968. Structural history and tectonics of Iran–a review. Bulletin of the Southwestern Association of Petroleum Geologists, 52(3): 1223–1258. https://doi.org/10.12691/ajmm-2-3-1

Tassara, S., González-Jiménez, J.M., Reich, M., Schilling, M.E., Morata, D., Begg, G. and Corgne, A., 2017. Plume-subduction interaction forms large auriferous provinces. Nature Communications, 8(4): 843–847. https://doi.org/10.1038/s41467-017-00821-z

Wedepohl, K.H., 1995. The composition of the continental crust. Geochimica and Cosmochimica Acta, 59(3): 217–239. https://doi.org/10.1016/0016-7037(95)00038-2

Wei, C., Huang, Z., Yan, Z., Hu, Y. and Ye, L., 2018. Trace element contents in sphalerite from the Nayongzhi Zn-Pb deposit, northwestern Guizhou, China: insights into incorporation mechanisms, metallogenic temperature and ore genesis. Minerals, 8(2): 490–498.  https://doi.org/10.3390/min8110490

Wu, Y.F., Fougerouse, D., Evans, K., Reddy, S.M., Saxey, D.W., Guagliardo, P. and Li, J.W., 2019. Gold, arsenic, and copper zoning in pyrite: A record of fluid chemistry and growth kinetics. Geology, 47(4): 641–644. https://doi.org/10.1130/G46114.1

Wu, Y., Hagni, R.D. and Paarlberg, N., 1994. Silver distribution in iron sulphides at the Buick and Brushy Creek Mines, Viburnum Trend, southeast Missouri. Economic Geology, 56(3): 577–587. https://doi.org/10.5382/SP.04.44

Xie, Z., Xia, Y., Cline, J.S., Koenig, A., Wei, D., Tan, Q. and Wang, Z., 2018. Are there Carlin-type gold deposits in China? A comparison of the Guizhou, China, deposits with Nevada, USA, deposits. Economic Geology, 20(5): 187–233. https://doi.org/10.5382/rev.20.06

Xing, Y., Brugger, J., Tomkins, A. and Shvarov, Y., 2019. Arsenic evolution as a tool for understanding formation of pyritic gold ores. Geology, 47(4): 335–338.  https://doi.org/10.1130/G46938Y.1

Xuexin, S., 1984. Minor elements and ore genesis of the Fankou lead-zinc deposit, China. Mineralium Deposita, 19(7): 95–104. https://doi.org/10.1007/BF00204667