Journal of Economic Geology (Aug 2024)
Intermediate-sulfidation epithermal base metal mineralization in the Kourcheshmeh deposit (SW Takestan): Constraints on geology, mineralization, and geochemistry
Abstract
Kourcheshmeh Pb-Zn-Cu deposit is located 40 km southwest of Takestan (Qazvin province) and west of the Mardabad-Bouinzahra volcanic belt. The mineralization occurred as Pb-Zn-Cu-bearing quartz veins hosted by early-middle Eocene tuff and lava strata and show a close spatial relationship with the middle Eocene pyroxene quartz monzodiorite body. The main ore vein ranges from 70 to 200 meters long, and 0.5 to 2 meters thick. Pyrite, chalcopyrite, galena, sphalerite, and tennantite-tetrahedrite, accompanied by minor pyrolusite and psilomelane, are the main ore minerals; quartz, calcite, siderite, barite, and sericite-illite are gangue minerals. Goethite, cerussite, smithsonite, malachite, and covellite are formed by supergene processes. The ore minerals formed as disseminated, vein-veinlets, brecciated, comb, crustiform, colloform, plumose, and vug infill textures. Six stages of mineralization can be distinguished at Kourcheshmeh, where Pb-Zn-Cu mineralization occurred as quartz-pyrite-chalcopyrite-galena-sphalerite ± tennantite-tetrahedrite veins and breccias in the second stage. Wall-rock alteration comprises silicification, intermediate argillic, carbonate, and propylitic alteration. Chondrite–normalized trace elements and REE patterns of ore samples, pyroxene quartz monzodiorite body, and fresh host acidic crystal tuff are comparable. This specifies that alteration and leaching of elements from the host volcanic rocks are involved in mineralization. Features of the Kourcheshmeh Pb-Zn-Cu deposit are similar to the intermediate-sulfidation type of epithermal deposits. Introduction The Urumieh-Dokhtar magmatic arc is a significant metalliferous province in Iran that hosts numerous Cu-Mo (Au) porphyry deposits (i.e., Sar Cheshmeh, Meiduk, Darreh-Zar, Chah-Firouzeh, Sarkuh, Iju, Aliabad, Kahang, and Dalli; McInnes et al., 2003; Zarasvandi et al., 2005; Taghipour et al., 2008; Ayati et al., 2013; Mirnejad et al., 2013; Aghazadeh et al., 2015; Alirezaei et al., 2017; Mohammaddoost et al., 2017; Golestani et al., 2018; Aliyari et al., 2020; Shafiei Bafti et al., 2022; Mohammaddoost et al., 2023) and epithermal precious and base metal (e.g., Sari Gunay, Touzlar, Chah Zard, Ay Qalasi, Milajerd, Chah-Mesi, and Govin; Richards et al., 2006; Kouhestani et al., 2012; Heidari et al., 2015; Kouhestani et al., 2015; Mohammadi Niaei et al., 2015; Kouhestani et al., 2017; Alipour-Asll, 2019; Zamanian et al., 2020; Altenberger et al., 2022) deposits. The Mardabad-Bouinzahra volcanic belt is located on the northern margin of the Urumieh-Dokhtar magmatic arc. This volcanic belt hosts several Manto-type Cu, and epithermal Au and Pb-Zn-Cu polymetallic deposits/occurrences like as Atash-Anbar, Lak, Deh-Bala, Ipak, Kuh-e Jarou, Rudak, Ghomoshlou, Ghomoshdash, Qezel-Ahmad, Bidestan, Afshar-Abad, Boujafar, Guilan-Darreh, Ramand, Hajib, Chalambar, and Kourcheshmeh (Habibi, 2007; Goodarzi, 2012; Ebrahimi, 2016; Yousefi et al., 2017; Tale Fazel et al., 2022a; Tale Fazel et al., 2022b; Khanahmadlou, 2023). Eocene volcanic and volcaniclastic rocks generally host these deposits and are temporally/spatially associated with middle Eocene intrusions (Kazemi et al., 2022). Kourcheshmeh Pb-Zn-Cu deposit is 40 km southwest of Takestan, Qazvin province, and part of the Mardabad-Bouinzahra volcanic belt. Despite the presence of ancient and new mining activities in the Kourcheshmeh area, no comprehensive studies have been conducted on the geology, mineralogy, geochemistry, and genesis of the Kourcheshmeh deposit. In this contribution, we investigate the detailed geology, mineralogy, structure and texture, geochemistry, and alteration styles of the Kourcheshmeh deposit to constrain its ore genesis and mineralization evolution. These outcomes might be useful for the regional exploration of epithermal base and precious metal deposits in the Mardabad-Bouinzahra volcanic belt and other parts of the Urumieh-Dokhtar magmatic arc. Materials and Methods During the fieldwork conducted on the Kourcheshmeh deposit, the following activities were carried out: - Preparation of a geological map, scale 1:5000, of the Kourcheshmeh deposit. - Collect approximately fifty samples from rock units, ore veins, and breccias. - Examination of seven thin sections and eighteen polished thin sections using a transmitted and reflected polarized light microscope in the University of Zanjan, Zanjan, Iran, laboratory. - Analysis of the chemical composition of ore samples (n = 28) and fresh and barren host rocks (n = 2) at the Zarazma Analytical Laboratories, Tehran, Iran, using XRF and ICP–MS methods. Results and Discussion The rock units outcropped in the Kourcheshmeh deposit comprise the Fajan Formation (conglomerate), Zyarat Formation (nummulitic limestone), Eocene volcanic (basalt, andesitic basalt, basaltic andesite, and megaporphyritic andesite) and volcaniclastic (intermediate crystal lithic tuff, and acidic crystal to lithic crystal tuff) strata, and Eocene-Oligocene (dacite, rhyodacite, rhyolite, and acidic tuff) sequence. The intrusive rock in the Kourcheshmeh area includes the middle Eocene (Kazemi et al., 2022) pyroxene quartz monzodiorite that cut the Eocene volcanic sequences. Mineralization at Kourcheshmeh occurred as Pb-Zn-Cu-bearing quartz veins within the Eocene tuff and lava sequence and is covered by a 3 m thickness of intermediate argillic alteration. The main ore vein has an N100E/70-80NE trend, 70 to 200 meters long, and 0.5 to 2 meters thick. Hydrothermal alteration includes silicification, intermediate argillic, carbonate, and propylitic alteration; the first three are directly linked to base metal mineralization. Pyrite, chalcopyrite, galena, sphalerite, tennantite-tetrahedrite, minor pyrolusite, and psilomelane, are the main ore minerals at Kourcheshmeh. Quartz, calcite, siderite, barite, and sericite-illite are gangue minerals. Goethite, cerussite, smithsonite, malachite, and covellite are formed by supergene processes. The ore minerals formed as disseminated, vein-veinlets, brecciated, comb, crustiform, colloform, plumose, and vug-infill textures. The mineralization processes at the Kourcheshmeh deposit can be divided into six stages, as follows: Stage 1: Silicification of host rocks with negligible disseminated pyrite. Stage 2: Quartz vein-veinlets and breccias that comprise mutable volumes of disseminated pyrite, chalcopyrite, galena, sphalerite, and minor tennantite-tetrahedrite. This stage is where Pb-Zn-Cu mineralization occurs. Stage 3: Barite vein-veinlets. Stage 4: Carbonate (calcite and siderite) and minor manganese ores (psilomelane, pyrolusite, braunite) as veinlets and vug-infill. Stage 5: Barren post-ore stage represented by calcite vein-veinlets. Stage 6: Supergene processes The Chondrite–normalized trace elements and REE patterns of ore samples, pyroxene quartz monzodiorite body, and fresh host acidic crystal tuff are comparable and show that host rocks are possibly engaged in mineralization. These patterns are almost similar for different ore samples, which can indicate the same mineralization system formed them. Characteristics of the Kourcheshmeh Pb-Zn-Cu deposit are similar to the intermediate-sulfidation type of epithermal deposits.
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