Dogan copper deposit (south of Shahroud): copper-molybdenum porphyry mineralization in the Toroud-Chah Shirin magmatic arc

Document Type : Research Article

Authors

1 Ph.D. student, Department of Geology, Faculty of Earth Sciences, Shahrood University of Technology, Shahrood, Iran

2 Associate professor, Department of Geology, Faculty of Earth Sciences, Shahrood University of Technology, Shahrood, Iran

3 Professor, Department of Geology, Institute of Mineralogy and Mineral Resources, Technical University of Clausthal, Clausthal-Zellerfeld, German

Abstract

The Dogan copper-molybdenum deposit is located in the northern Central Iranian magmatic arc, south of Shahrood. Mineralization in this area is caused by the injection of a microdioritic subvolcanic intrusion into Eocene volcanic rocks. Mineralization occurs frequently as veins, veinlets, and disseminated ores and is mineralogically composed of primary minerals like pyrite, chalcopyrite, bornite, and molybdenite as well as secondary minerals like chalcocite, iron oxides and hydroxides, and malachite. The alteration zoning in the Dogan deposit is circular and concentric and changes from potassic in the central part to phyllic alteration and then propylitic alteration in the margins. Some parts of argillic alteration are observed in the upper and surface parts of the phyllic zone. The fluids producing potassic alteration were rich in liquid and a small amount of steam (L + V), had a high temperature (398 to 513ºC), and a high salinity (50 wt% NaCl), according to fluid inclusions studies. These fluids were most likely magmatic in origin and were responsible for the formation of the V1 and V2 veins. The activity of meteoric fluids containing liquid vapor phases (V + L) with lower temperature (210 to 360°C) and salinity less than 10 wt % NaCl causes phyllic alteration (V3 veins). In terms of geochemistry, the studied igneous samples are adakititc in nature and are located in the domain of calc-alkaline magmas of the active continental margin. The presence of potassic alteration in surface and deep cores, the high salinity and temperature of hydrothermal fluids, the type of mineralization (disseminated and vein-veinlet), the high potential of copper and molybdenum, and the zonation of existing alterations are all indicative of a porphyry system. The Dogan mining area is similar to copper-molybdenum porphyry deposits in terms of tectonic environment of formation, host rock type, texture and structure, mineralogy, and alteration zonation.
 
 
Introduction
One of the ore-bearing magmatic arcs in the northern structural zone of Central Iran is the Toroud-Chah-Shirin magmatic arc (TCMA) (Fig. 1A). It hosts a significant volume of Eocene volcanic and pyroclastic rocks and equivalent subvolcanic and intrusive bodies. According to the distribution of mineralized systems in the aforementioned magmatic arc, the majority of the ore deposits under investigation are epithermal (see, for instance, Sheibi and Mousivand, 2018;  Mehrabi and Ghasemi Siani, 2012; Tale Fazel et al., 2019). This study has shown the geological proof of a typical Cu-Mo porphyry ore deposit at Dogan, which is 130 km southeast of Shahrood (in the province of Semnan) and 18 km north of the village of Toroud.
 
Materials and methods
Precise microscopic investigations of mineralogy, texture, and mineralography were made on 10 thin and 27 thin-polished sections. In the Vancouver (ACME) laboratory in Canada and the TU Clausthal laboratory (IELF) in Germany, whole rock geochemistry of microdioritic samples with the least alteration was examined by XRF, ICP-OES and ICP-MS methods. Fluid inclusion thermometry is measured using the Linkham MDSG600 heating/freezing stage at the economic geology laboratory of the Shahrood University of Technology. At the Clausthal Laboratory (IELF) in Germany, the Linkham MDSG600 heating/freezing stage and the XRD methods have been used to identify some very fine fluid inclusion analyses and clay minerals, respectively.
 
Results
A subvolcanic intrusion was introduced into Eocene volcanic rocks, resulting in the development of the Dogan Cu-Mo deposit. The microdiorites have a distinct LREE/HREE fractionation and are enriched in large ion lithophile elements (LILE) and depleted in high field-strength elements (HFSE). In addition, the Nb and Ti negative anomalies indicate a magmatic arc signature. However, they differ from typical volcanic arc magmas geochemically due to having SiO2 ≥40 wt.%, Al2O3≥10 wt%, 1<MgO<5 wt%, Sr≥200 and Y>18 ppm, along with the depletion of HREE have adakititc affinities. Based on field and laboratory studies, potassic alteration, propylitic, phyllic, argillic alterations have been detected in the Dogan deposit. Potassic alteration is located in the central part of the system and varies from abundant potassium feldspar veins in the superficial parts to microdiorite containing abundant hydrothermal biotites and potassium feldspar in boreholes. For the samples that have undergone potassic alteration, the fluid inclusion homogenization temperature is greater than 590°C and is similar to values found in other porphyry deposits. This alteration also led to the formation of two known mineralized veins, namely V1: quartz + potassium feldspar + biotite + pyrite + magnetite + chalcopyrite, and V2: potassium feldspar + anhydrite/gypsum + pyrite + molybdenite + chalcopyrite. Sericitic (phyllic) alteration in Dogan is frequently restricted to the fractures where quartz, sericite, and pyrite have been produced as a result of hydrolysis of the potassic- altered rocks.
In phyllic altered rocks, the majority of third type veins (V3) containing quartz and trace amounts of pyrite + chalcopyrite ± bornite have been observed. Like many copper and copper-molybdenum porphyry systems (for example: Lepanto Far Southeast deposit in Hedenquist et al., 1998), advanced argillic alteration is observed exactly in the upper part of the Dogan deposit. Significant amounts of Na, Ca, and Mg are removed from the structure of pre-existing minerals during this process due to the low pH (Clark et al., 2003). Propylitic alteration is found at the periphery, from the surface to medium depths, and close to phyllic and argillic alteration in the Dogan deposit.
 
Discussion
The microdirotic intrusion has formed at an active continental margin with an adakitic nature. The hypogene sulfide mineralization occurs mainly as disseminated chalcopyrite and pyrite, typically in the matrix or associated stockworks containing potassium feldspar-gypsum/anhydrite, especially in the rocks affected by potassic and phylic processes. The fluids producing potassic alteration are rich in liquid and less vapor (LV); they have high temperatures (398 to 513°C) and high salinity (more than 50 wt% NaCl). These fluids have a magmatic origin and are considered to be the cause of mineralized veins. Phyllic alteration is caused by the activity of fluids containing vapor and liquid phases at lower temperatures (210 to 360°C) and less than 10 wt% NaCl salinity.
The low temperature homogenization of the fluid inclusions in phyllic altered rocks (210°C) indicates that the thermal gradients have decreased and the meteoric fluids have flowed. In the next stage with decreasing temperature, the addition of significant amounts of meteoric fluids causes Na-Mg-Ca metasomatism and a mineral assemblage of propylitic alteration, i.e., epidote, chlorite and calcite. The subvolcanic nature of the host rocks (microdiorite) and their formation in the magmatic arc, the presence of potassic alteration evidence in surface and drilled cores, the salinity and high temperature of hydrothermal fluids, the type of mineralization (disseminate and vein-veinlet), the high potential of copper and molybdenum, and zonation of existing alterations all indicate the occurrence of a porphyry system. Geologists should be motivated by the supplied information to look for undiscovered porphyry systems in the Toroud-Chah-Shirin and other Iranian magmatic arcs.
 
Acknowledgments
We sincerely thank Tavan Energy Resources Development Company for providing access to the boreholes and support on the field.

Keywords


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
Bodnar, R.‌J., 1993. Revised equation and table for determining the freezing point depression of H2O-NaCl solutions. Geochimica et Cosmochimica acta, 57(3): 683–684. https://doi.org/10.1016/0016-7037(93)90378-A
Boynton, W.V., 1984. Geochemistry of the rare earth elements: meteorites studies. In: P. Henderson (Editor), Rare Earth Element Geochemistry. Elsevier, Amsterdam, pp. 63–114. https://doi.org/10.1016/B978-0-444-42148-7.50008-3
Calagari, A.A., 1997. Geochemical, stable isotope, noble gas and fluid inclusion studies of mineralization and alteration at Sungun porphyry copper deposit, East Azarbaidjan, Iran: Implications for genesis. Ph.D. Thesis, the University of Manchester, Manchester, England, 550 pp. Retrieved April 26, 2023 from https://www.proquest.com/openview/c4af0175edfcdd6c68aa05f548baef45
Clark, D.A., Geuna, S. and Schmidt, P.W., 2003. Predictive magnetic exploration models for porphyry, epithermal and iron oxide copper‐gold deposits: Implications for exploration. AMIRA Exploration and Mining Report 1073R, 398 pp.
Dilles, J.H. and Einaudi, M.T., 1992. Wall-rock alteration and hydrothermal flow paths about the Ann-Mason porphyry copper deposit, Nevada; a 6-km vertical reconstruction. Economic Geology, 87(8): 1963–2001. https://doi.org/10.2113/gsecongeo.87.8.1963
Guilbert, J.M. and Park, C.F., 1986. The Geology of Ore Deposits. Freeman, New York, 650 pp.
Gustafson, L.B. and Hunt, J.P., 1975. The porphyry copper deposit at El Salvador, Chile. Economic Geology, 70(5): 857–912. https://doi.org/10.2113/gsecongeo.70.5.857
Hedenquist, J.W., Arribas, A. and Reynolds, T.J., 1998. Evolution of an intrusion-centered hydrothermal system; Far Southeast-Lepanto porphyry and epithermal Cu-Au deposits, Philippines. Economic Geology, 93(4): 373–404. https://doi.org/10.2113/gsecongeo.93.4.373
Houshmandzadeh, A.R., Alavi Naini, M. and Haghipour, A.A., 1978. Evolution of geological phenomenon in Torud area. Geological Survey of Iran, Tehran, Report 5H, 136 pp. (in Persian)
Irvine, T.‌N. and Baragar, W.‌R.‌A., 1971. A guide to the chemical classification of the common volcanic rocks. Canadian Journal of Earth Sciences, 8(5): 523–548. https://doi.org/10.1139/e71-055
John, D.‌A., Ayuso, R.‌A., Barton, M.‌D., Blakely, R.J., Bodnar, R.‌J., Dilles, J.‌H. and Vikre, P.‌G., 2010. Porphyry copper deposit model. Chapter B of Mineral deposit models for resource assessment.US Geological Survey, Reston, VA, Scientific Investigations Report 2010-5070-B, 169 pp. https://doi.org/10.3133/sir20105070B
Lang, J.R. and Titley, S.R., 1998. Isotopic and geochemical characteristics of Laramide magmatic systems in Arizona and implications for the genesis of porphyry copper deposits. Economic Geology, 93(2): 138–170. https://doi.org/10.2113/gsecongeo.93.2.138
Martin, H., 1999. Adakitic magmas: modern analogues of Archaean granitoids. Lithos, 46(3): 411–429. https://doi.org/10.1016/S0024-4937(98)00076-0
Mehrabi, B. and Ghasemi Siani, M., 2012. Intermediate sulfidation epithermal Pb-Zn-Cu (±Ag-Au) mineralization at Cheshmeh Hafez deposit, Semnan province, Iran. Journal of the Geological Society of India, 80(4): 563–578. https://doi.org/10.1007/s12594-012-0177-x
Moyle, A.J., 1990. Ladolam gold deposit, Lihir island. In: F.E. Hughes (Editor), Geology of the mineral deposits of Australia and Papua New Guinea. Melbourne, Australian Institute of Mining and Metallurgy, pp. 1793–1805.
Pearce, J.A., 1983. Role of the sub-continental lithosphere in magma genesis at active continental margins. In: C.J. Hawkesworth and M.J. Norry (Editors), Continental basalts and mantle xenoliths, Nantwich, Cheshire: Shiva Publications, pp. 230–249. Retrieved Jun 04, 2017 from https://orca.cardiff.ac.uk/id/eprint/8626
Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25(4): 956–983. https://doi.org/10.1093/petrology/25.4.956
Perelló, J., Sillitoe, R.H., Mpodozis, C., Brockway, H. and Posso, H., 2012. Geologic setting and evolution of the porphyry copper-molybdenum and copper-gold deposits at Los Pelambres, central Chile. In: J.F. Hedenquist, M. Harris and F. Camus (Editors), Geology and Genesis of Major Copper Deposits and Districts of the World: A Tribute to Richard H. Sillitoe. Geo Science world, Tysons Galleria, 79–104. Retrieved January 01, 2012 from https://pubs.geoscienceworld.org/segweb/books/book/1385/chapter-abstract/107046729/Geologic-Setting-and-Evolution-of-the-Porphyry?redirectedFrom=fulltext
Richards, J.P., Boyce, A.J. and Pringle, M.S., 2001. Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization. Economic Geology, 96(2): 271–305. https://doi.org/10.2113/gsecongeo.96.2.271
Ronacher, E., Richards, J.P. and Johnston, M.D., 2000. Evidence for fluid phase separation in high-grade ore zones at the Porgera gold deposit, Papua New Guinea. Mineralium Deposita, 35(7): 683–688. https://doi.org/10.1007/s001260050271
Rowins, S.M., 2000. Reduced porphyry copper-gold deposits: A new variation on an old theme. Geology, 28(6): 491–494. https://doi.org/10.1130/0091-7613(2000)28<491:RPCDAN>2.0.CO;2
Rudnick, R.L. and Gao, S. 2003. Composition of the Continental Crust. In: H.D. Holland and K.K. Turekian, (Editors), Treatise on Geochemistry, V. 3, The Crust, Elsevier-Pergamon, Oxford, pp. 1–64.
Sheibi, M. and Mousivand, F., 2018. Petrology, geochemistry and magnetic susceptibility of Chah-Musa pluton- host of Cu mineralization- (NW Toroud, South Shahrood) with special reference to the mineralization. Middle East Mines & Mineral Industries Development Holding Company of Iran, Tehran, unpublished Report 1, 200 pp. (in Persian)
Sillitoe, R.H., 2010. Porphyry copper systems. Economic Geology, 105(1): 3–41. https://doi.org/10.2113/gsecongeo.105.1.3
Sun, S.S. and McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society, London, Special Publications, 42(1): 313–345. https://doi.org/10.1144/GSL.SP.1989.042.01.19
Sun, W., Huang, R., Li, H., Hu, Y., Zhang, C., Sun, S., Zhang, L., Ding, X., Li, C., Zartman, R.E. and Ling, M., 2015. Porphyry deposits and oxidized magmas. Ore Geology Reviews, 65 (part 1): 97–131. https://doi.org/10.1016/j.oregeorev.2014.09.004
Tadayon, M. and Rashid Katal, R.K., 2020. Structural analysis of the Dogan copper mine area, north Toroud fault zone (Central Iran). Journal of Tectonics, 4(13): 87–111. (in Persian with English abstract) https://doi.org/10.22077/jt.2021.1603
Tale Fazel, E., Mehrabi, B. and GhasemiSiani, M., 2019. Epithermal systems of the Torud–Chah Shirin district, northern Iran: Ore-fluid evolution and geodynamic setting. Ore Geology Reviews, 109: 253–275. https://doi.org/10.1016/j.oregeorev.2019.04.014
Warr, L.N., 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3): 291–320. https://doi.org/10.1180/mgm.2021.43
Waterman, G. ‌C. and Hamilton, R.‌L., 1975. The Sar Cheshmeh porphyry copper deposit. Economic Geology, 70(3): 568–576. https://doi.org/10.2113/gsecongeo.70.3.568
Wilkinson, J.J., 2001. Fluid inclusions in hydrothermal ore deposits. Lithos, 55‌(1–4): 229–272. https://doi.org/10.1016/S0024-4937(00)00047-5
Wilson, M., 1989. Igneous Petrogenesis: A Global Tectonic Approach. Unwin Hyman, London, 466 pp. https://doi.org/10.1007/978-1-4020-6788-4
Winchester, J.A. and Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, 20: 325–343. https://doi.org/10.1016/0009-2541(77)90057-2
Zarasvandi, A., Liaghat, S. and Zentilli, M., 2005. Geology of the Darreh-Zerreshk and Ali-Abad porphyry copper deposits, central Iran. International Geology Review, 47(6): 620–646. https://doi.org/10.2747/0020-6814.47.6.620
CAPTCHA Image