Intermediate-sulfidation epithermal base and precious metal mineralization in the Qebchaq deposit (NW Qarachaman, East Azerbaijan): Geology, mineralization, and geochemical evidence

Document Type : Research Article

Authors

• Mohammad Sohbatloo ¹
• Hossein Kouhestani ²
• Mir Ali Asghar Mokhtari ²

¹ M.Sc., Department of Geology, University of Zanjan, Zanjan, Iran

² Associate Professor, Department of Geology, University of Zanjan, Zanjan, Iran

10.22067/econg.2022.75340.1041

Abstract

Precious and base metal mineralization in the Qebchaq deposit occurred as brecciated quartz-sulfide veins within the Eocene tuff and lava strata, and the Oligocene quartz diorite-gabbro intrusion. Pyrite, chalcopyrite, galena, sphalerite, and gold along with minor realgar, psilomelane, and pyrolusite, are ore minerals; quartz, sericite, chlorite and calcite are gangue minerals. The ore minerals show disseminated, vein-veinlet, brecciated, comb, cockade, colloform, crustiform, plumose, and vug infill textures. Five stages of mineralization can be distinguished at Qebchaq. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. Stage 2 is characterized by quartz veins and breccias that contain variable amounts of disseminated pyrite, chalcopyrite, galena, sphalerite ± native gold ± realgar. Stage 3 is marked by quartz-manganese oxides-hydroxides (psilomelane, pyrolusite, braunite) veins and hydrothermal breccia cements. Stage 4 is represented by quartz (calcite-chlorite) vein-veinlets, and stage 5 is characterized by calcite as veinlets and vug infill texture. Wall-rock alterations include silicification, intermediate argillic, carbonate, chlorite and propylitic alteration. Chondrite–normalized trace elements and REE patterns of the mineralized samples and the host rocks are similar and indicate that host rocks are probably involved in mineralization. Characteristics of Qebchaq deposit are comparable with intermediate-sulfidation type of epithermal deposits.
 
Introduction
Qebchaq base and precious metal deposit, 15 km northwest of Qarachaman, is located in the Western Alborz–Azerbaijan zone, northwestern Iran. Several types of deposits are present in this zone including porphyry and skarn Cu-Mo (Au) porphyry deposits, Cu-Mo and Fe skarn deposits, Cu-Mo-Au vein deposits, and epithermal Au deposits (Jamali et al., 2010; Kouhestani et al., 2018). The most important deposit discovered to date within the Western Alborz–Azerbaijan zone is the Sungun porphyry Cu-Mo deposit, which has a defined reserve of 796 Mt at 0.6% Cu (Hezarkhani and Williams-Jones, 1998; Aghazadeh et al., 2015; Simmonds et al., 2017). Other important deposits or occurrences include Haft-Cheshmeh, Sonajil, Ali Javad, Mirkuh-e-Ali Mirza, Astergan, Avan, Anjerd, Mazraeh, Astamal, Pahnavar, Masjed Daghi, Sharafabad, Mivehroud, Nabijan, Zaglig, Aniq, Zaily Darreh, Qara Darreh and Qarachilar (Ebrahimi et al., 2011; Jamali et al., 2010; Mokhtari, 2012; Maghsoudi et al., 2014; Mokhtari et al., 2014; Adeli et al., 2015; Baghban et al., 2015; Baghban et al., 2016; Simmonds and Moazzen, 2015; Kouhestani et al., 2018).
Although geological general characteristics of the location of the Qebchaq deposit have been determined (Asadian et al., 1993), no detailed studies have been conducted on the mineralogy, geochemistry, and genesis of the Qebchaq deposit. In this paper, detailed geology, mineralogy, geochemistry, and alteration styles of the Qebchaq deposit to constrain its ore genesis are investigated. These results may have implications for the regional exploration of epithermal base and precious metal deposits in the Western Alborz–Azerbaijan zone.
 
Material and Methods 
Detailed fieldwork has been carried out at different scales in the Qebchaq area. A total of 50 samples were collected from various parts of ore veins and breccias, host volcanic rocks, and intrusions. The samples were prepared for thin (n=8) and polished-thin (n=32) sections in the laboratory at the University of Zanjan, Zanjan, Iran. Thirty nine representative samples from the mineralized veins and breccias, 1 sample from host dacitic rocks, and 1 sample from altered quartz diorite-gabbro intrusion were analyzed for REE, Au, Ag, Cu, Pb, Zn, and other rare elements using Fire Assay and ICP–MS in the Zarazma Analytical Laboratories, Tehran, Iran.
 
Results and Discussion
The geological units hosting the Qebchaq deposit are mainly Eocene volcanic and volcaniclastic rocks that have been intruded by Oligocene intrusions. The Eocene sequence includes tuff, andesite, and andesitic basalt, rhyolite, rhyodacite-dacite, and ignimbrite. The intrusive rocks in the Qebchaq area include Oligocene quartz diorite-gabbro and granite-alkali granite. They show porphyritic, microgranular, and granular textures. Mineralization at Qebchaq occurs as the epithermal base and precious metal quartz-sulfide brecciated vein that occupies NE-trending faults in the Eocene volcanic rocks and Oligocene intrusions.  The ore veins are 50 to 1000 m long, from 0.5 to 4 m wide, and generally, dip steeply (65–85°) to the southeast and northwest. Wall-rock alterations developed at the Qebchaq deposit include silicification, intermediate argillic, carbonate, chlorite, and propylitic alteration. The first four types are closely related to mineralization. Five stages of mineralization can be distinguished at Qebchaq. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. This stage is usually crosscut by stage 2. Stage 2 (the main ore-stage) is characterized by millimeters to several centimeters wide quartz veins and breccias that contain variable amounts of disseminated pyrite, chalcopyrite, galena, sphalerite ± native gold ± realgar. Clasts of this stage and associated wall-rock alteration have been recognized in the hydrothermal cement of stage 3 breccias. Stage 3 is marked by quartz- manganese oxides-hydroxides (psilomelane, pyrolusite, braunite) veins and breccia cement. It is usually crosscut stage 2 and is cut by stage 4 veinlets. Stage 4 is represented by < 1 mm wide quartz (calcite-chlorite) vein-veinlets. This stage usually crosscuts previous ore stages. No sulfide minerals are recognized in stage 4. Stage 5 is characterized by up to 2 mm wide veinlets or vug infill texture of calcite. Stage 5 calcite veinlets usually crosscut previous ore stages. The ore minerals at Qebchaq have been formed as vein-veinlet and hydrothermal breccia cement, and show disseminated, vein-veinlet, brecciated, comb, cockade, colloform, crustiform, plumose, and vug infill textures. Pyrite, chalcopyrite, galena, sphalerite, native gold, realgar, psilomelane, and pyrolusite are the main ore minerals. Malachite, azurite, smithsonite, cerussite, goethite, secondary pyrolusite, and braunite are supergene minerals. Quartz, sericite, chlorite, and calcite are present in the gangue minerals. 
Comparison of Chondrite–normalized rare elements and REE patterns of host dacitic lavas, fresh and altered quartz diorite-gabbro intrusion, and the mineralized samples at Qebchaq indicate that leaching of some elements from the host rock units may have been involved in mineralization. The data in this study suggest that Qebchaq is an example of intermediate-sulfidation type of epithermal base and precious metal mineralization.

Keywords

• Epithermal mineralization
• Base and precious metal
• Intermediate-sulfidation
• Qebchaq
• Qarachaman

20.1001.1.20087306.1402.15.1.3.1

---

References

Adeli, Z., Rasa, I. and Darvishzadeh, A., 2015. Fluid inclusion study of the ore-quartz veins at

Haftcheshmeh porphyry copper (Mo) deposit, Ahar–Arasbaran Magmatic Belt, NW Iran. Ore Geology Reviews, 65‌(2): 502–511. https://doi.org/10.1016/j.oregeorev.2014.05.022

Aghazadeh, M., Hou, Z., Badrzadeh, Z. and Zhou, L., 2015. Temporal–spatial distribution and

tectonic setting of porphyry copper deposits in Iran: constraints from zircon U-Pb and molybdenite Re–Os geochronology. Ore Geology Reviews, 70: 385–406. https://doi.org/10.1016/j.oregeorev.2015.03.003

Albinson, T., Norman, D.I., Cole, D. and Chomiak, B., 2001. Controls on formation of low-sulfidation epithermal deposits in Mexico: Constraints from fluid inclusion and stable isotope data. In: T. Albinson and C.E. Nelson (Editors), New Mines and Discoveries in Mexico and Central America. Society of Economic Geologists, Littleton, pp. 1–32.  https://doi.org/10.5382/SP.08.01

Asadian, A., Amini Fazl., A. and Khodabandeh, A., 1993. Geological map of Torkamanchay-Qarachaman, scale 1:100,000. Geological Survey of Iran.

Baghban, S., Hosseinzadeh, M.R., Moayyed, M., Mokhtari, M.A.A. and Gregory, D., 2015.

Geology, mineral chemistry and formation conditions of calc-silicate minerals of Astamal Fe-LREE distal skarn deposit, Eastern Azarbaijan Province, NW Iran. Ore Geology Reviews, 68: 79–96. https://doi.org/10.1016/j.oregeorev.2014.12.016   

Baghban, S., Hosseinzadeh, M.R., Moayyed, M., Mokhtari, M.A.A., Gregory, D. and Mahmoudi Nia, H., 2016. Chemical composition and evolution of the garnets in the Astamal Fe-LREE distal skarn deposit, Qara-Dagh–Sabalan metallogenic belt, Lesser Caucasus, NW Iran. Ore Geology Reviews, 78: 166–175. https://doi.org/10.1016/j.oregeorev.2016.02.020

Behrouzi, A., Amini Fazl, A. and Amini Azar, R., 1998. Geological map of Bostanabad, scale 1:100,000. Geological Survey of Iran.

Bienvenu, P., Bougault, H., Joron, J.L., Treuil, M. and Dmitriev, L. 1990. MORB alteration: Rare earth element/non-rare hydromagmaphile element fractionation. Chemical Geology, 82: 1–14.  https://doi.org/10.1016/0009-2541(90)90070-N

Ebrahimi, S., Alirezaei, S. and Yuanming, P., 2011. Geological setting, alteration, and fluid

inclusion characteristics of Zaglic and Safikhanloo epithermal gold prospects, NW Iran. In: A.N. Sial, J.S. Bettencourt, C.P. De Campos and V.P. Ferreira (Editor), Granite Related Ore Deposits: An Introduction. Geological Society of London, Special Publication, London, 350, pp. 133–147. https://doi.org/10.1144/SP350.8

Ebrahimi, S., Pan, Y., Alirezaei, S. and MehrPartou, M., 2009. Fluid inclusion and mineralogical studies of the Sharafabad epithermal gold deposit, NW Iran. Scientific Quarterly Journal of Geosciences, 18‌(71): 149–154. http://dx.doi.org/10.22071/gsj.2010.57004

Einaudi, M.T., Hedenquist, J.W. and Inan, E.E., 2005. Sulfidation state of fluids in active and extinct hydrothermal systems: Transitions from porphyry to epithermal environments. In: S.F. Simmons and I. Graham (Editors), Volcanic, geothermal, and ore-forming fluids: rulers and witnesses of processes within the earth. Society of Economic Geologists, Littleton, pp. 285–313. https://doi.org/10.5382/SP.10.15

Gemmell, J. B., 2004.  Low- and intermediate-sulfidation epithermal deposits. In: D.R. Cooke, C.L. Deyel and J. Pongratz (Editors), 24 Ct Gold Workshop. University of Tasmania, Hobart, Australia, pp. 57–63. Retrieved July 20, 2022 from http://catalogobiblioteca.ingemmet.gob.pe/cgi-bin/koha/opac-detail.pl?biblionumber=40195

Ghorbani, A., Kouhestani, H. and Mokhtari, M.A.A., 2022. Genesis of the Varmazyar Pb–Zn (Ag) occurrence, Tarom-Hashtjin metallogenic belt: Insights from ore geology, geochemistry and fluid inclusion studies. Journal of Economic Geology, 14‌ (1): 1–38. (in Persian with extended English abstract) https://doi.org/10.22067/econg.2021.51947.86716

Hedenquist, J.W., Arribas, A. and Gonzalez-Urien, E., 2000. Exploration for epithermal gold deposits. In: S.G. Hagemann and P.E. Brown (Editors), Gold in 2000. Society of Economic Geologists, Littleton, pp. 245–277. https://doi.org/10.5382/Rev.13.07

Hezarkhani, A. and Williams-Jones, A.E., 1998. Controls of alteration and mineralization in the Sungun porphyry copper deposit, Iran: evidence from fluid inclusions and stable isotopes. Economic Geology, 93: 651–670. https://doi.org/10.2113/gsecongeo.93.5.651

Humphris, S.E., 1984. The mobility of the rare earth elements in the crust. In: P. Henderson (Editor), Developments in Geochemistry. Elsevier, Amsterdam, pp. 317–342.  https://doi.org/10.1016/B978-0-444-42148-7.50014-9

Jamali, H., Dilek, Y., Daliran, F., Yaghubpur, A.M. and Mehrabi, B., 2010. Metallogeny and tectonic evolution of the Cenozoic Ahar-Arasbaran volcanic belt, northern Iran. International Geology Review, 52 (2): 608–630. https://doi.org/10.1080/00206810903416323

Khodabandehlou, Z., Ghaderi, M. and Rastad, E., 2018. Mineralogy, texture and structure, and formation stages of the Golijeh intermediate-sulfidation epithermal deposit in Tarom subzone of western Alborz – Azerbaijan zone. Advanced Applied Geology, 8‌(2): 9–20. https://doi.org/10.22055/aag.2018.24286.1802

 Kouhestani, H., Mokhtari, M.A.A., Chang, Z. and Johnson, A.C., 2018. Intermediate-sulfidation type base metal mineralization at Aliabad–Khanchy, Tarom–Hashtjin metallogenic belt. NW Iran. Ore Geology Reviews, 93: 1–18. https://doi.org/10.1016/j.oregeorev.2017.12.012

Kouhestani, H., Mokhtari, M.A.A., Qin, K.Z. and Zhao, J.X., 2019a. Fluid inclusion and stable isotope constraints on ore genesis of the Zajkan epithermal base metal deposit, Tarom–Hashtjin metallogenic belt, NW Iran. Ore Geology Reviews, 109: 564–584. https://doi.org/10.1016/j.oregeorev.2019.05.014

Kouhestani, H., Mokhtari, M.A.A., Qin, K.Z. and Zhao, J.X., 2019b. Origin and evolution of hydrothermal fluids in the Marshoun epithermal Pb–Zn–Cu (Ag) deposit, Tarom–Hashtjin metallogenic belt, NW Iran. Ore Geology Reviews, 113: 103087. https://doi.org/10.1016/j.oregeorev.2019.103087

Kouhestani, H., Mokhtari, M.A.A., Qin, K.Z. and Zhang, X.N., 2020. Genesis of the Abbasabad epithermal base metal deposit, NW Iran: Evidences from ore geology, fluid inclusion and O–S isotopes. Ore Geology Reviews, 126: 103752. https://doi.org/10.1016/j.oregeorev.2020.103752

Kouhestani, H., Mokhtari, M.A.A. and Zhang, X.N., 2022. Fluid inclusion and stable isotope constraints on the genesis of epithermal base-metal veins in the Armaqan Khaneh mining district, Tarom-Hashtjin

metallogenic belt, NW Iran. Australian Journal of Earth Sciences, 69‌(6): 844–860. https://doi.org/10.1080/08120099.2022.2033320

Lottermoser, B.G., 1992. Rare earth elements and hydrothermal ore formation processes. Ore Geology Reviews, 7 (1): 25–41. https://doi.org/10.1016/0169-1368(92)90017-F   

Maghsoudi, A., Yazdi, M., Mehrpartou, M., Vosoughi, M. and Younesi, S., 2014. Porphyry Cu–Au mineralization in the Mirkuh-e-Ali Mirza magmatic complex, NW Iran. Journal of Asian Earth Sciences, 79‌(B): 932–941. https://doi.org/10.1016/j.jseaes.2012.10.002

Mehrabi, B., Ghasemi Siani, M., Goldfarb, R., Azizi, H., Ganerod, M. and Marsh, E.E., 2016. Mineral assemblages, fluid evolution and genesis of polymetallic epithermal veins, Gulojeh district, NW Iran. Ore Geology Reviews, 78: 41–57. https://doi.org/10.1016/j.oregeorev.2016.03.016

Mokhtari, M.A.A., 2012. The mineralogy and petrology of the Pahnavar Fe skarn, in the Eastern Azarbaijan, NW Iran. Central European Journal of Geosciences, 4‌(4): 578–591. https://doi.org/10.2478/s13533-012-0106-y

Mokhtari, M.A.A., Moinvaziri, H., Ghorbani, M.R. and Mehrpartou, M., 2014. Geology and Geochemistry of Aniq-Qarachilar Au- Cu- Mo Mineralization (NE of Kharvana, Eastern Azarbaijan). Scientific Quarterly Journal of Geosciences, 23 (4): 135–150. http://dx.doi.org/10.22071/gsj.2014.43973

Murphy, J.B. and Hynes, A.J., 1986. Contrasting secondary mobility of Ti, P, Zr, Nb and Y in two meta-basaltic suites in the Appalachians. Canadian Journal of Earth Sciences, 23‌(8): 1138–1144.  https://doi.org/10.1139/e86-112

Nabavi, M.H., 1976. An introduction to geology of Iran. Geological Survey of Iran, Tehran, 109 pp. (in Persian)

Nakamura, N. 1974. Determination of REE, Ba, Fe, Mg, Na and K in Carbonaceous and Ordinary Chondrites. Geochimica et Cosmochimica Acta, 38 (5): 757–775. http://dx.doi.org/10.1016/0016-7037(74)90149-5

Salehi, T., Ghaderi, M. and Rashidnejad-Omran, N., 2011. Mineralogy and geochemistry of rare earth elements in Qomish Tappeh Zn–Pb–Cu (Ag) deposit, southwest of Zanjan. Journal of Economic Geology, 2 (2): 235–254. (in Persian with English abstract) https://doi.org/10.22067/ECONG.V2I2.7853    

Salehi, T., Ghaderi, M. and Rashidnejad-Omran, N., 2015. Epithermal base metal-silver mineralization at Qomish Tappeh deposit, southwest of Zanjan. Scientific Quarterly Journal, Geosciences, 25‌(97): 329–346. (in Persian with English abstract)  https://doi.org/10.22071/GSJ.2015.41519    

Sillitoe, R.‌H. and Hedenquist, J.‌W., 2003. Linkages between volcanotectonic settings, ore fluid

compositions, and epithermal precious-metal deposits. In: S.F. Simmons and I. Graham (Editors), Volcanic, Geothermal, and Ore-Forming Fluids: Rulers and Witnesses of Processes Within the Earth. Economic Geology Special Publication 10, Littleton, pp. 315–343. Retrieved July 20, 2022 from https://www.researchgate.net/publication/285488888

Simmonds, V. and Moazzen, M., 2015. Re–Os dating of molybdenites from Oligocene Cu–Mo–Au mineralized veins in the Qarachilar area, Qaradagh batholith (northwest Iran): Implications for understanding Cenozoic mineralization in South Armenia, Nakhchivan and Iran. International Geology Review, 57 (3): 290–304. https://doi.org/10.1080/00206814.2014.1003339

Simmonds, V., Moazzen, M. and Mathur, R., 2017. Constraining the timing of porphyry mineralization in northwest Iran in relation to Lesser Caucasus and Central Iran; Re–Os age data for Sungun porphyry Cu–Mo deposit. International Geology Review, 59‌(12): 1561–1574. https://doi.org/10.1080/00206814.2017.1285258

Simmons, S.F., White, N.C. and John, D.A., 2005. Geological characteristics of epithermal precious and base metal deposits. In: J.W. Hedenquist, J.F.H. Thompson, R.J. Goldfarb and J.P. Richards (Editors), One Hundredth Anniversary Volume. Society of Economic Geologists, Littleton, pp. 485–522. https://doi.org/10.5382/AV100.16

Sohbatloo, M., 2022. Geology, geochemistry and genesis of Qebchaq base and precious metals mineralization, NW Qarehchaman. Unpublished M.Sc. Thesis, University of Zanjan, Zanjan, Iran, 105 pp. (in Persian with English abstract)

Thompson, R.N., 1982. Magmatism of the British Tertiary volcanic province. Scottish Journal of Geology, 18‌(1): 49–107. https://doi.org/10.1144/sjg18010049 

Verdel, C., Wernicke, B.P., Hassanzadeh, J. and Guest, B., 2011. A Paleogene extensional arc flare-up in Iran. Tectonics 30‌(3). https://doi.org/10.1029/2010TC002809 

Wang, L., Qin, K.Z., Song, G.Y. and Li, G.M., 2019. A review of intermediate sulfidation epithermal deposits and subclassification. Ore Geology Reviews, 107: 434–456. https://doi.org/10.1016/j.oregeorev.2019.02.023

Whitford, D.J., Korsch, M.J., Porritt, P.M. and Craven, S.J., 1988. Rare earth element mobility around the volcanogenic polymetallic massive sulfide deposit at Que River, Tasmania, Australia. Chemical Geology, 68‌(1–2): 105–119. https://doi.org/10.1016/0009-2541(88)90090-3

Whitney, D.L. and Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist, 95‌(1): 185–187. https://doi.org/10.2138/am.2010.3371