University of Isfahan Petrological Journal 2228-5210 16 3 2025 09 23 Kuroko-type Pb-Zn sulfide deposit at Chah Gaz region, Sanandaj-Sirjan Zone, Kerman Province Kuroko-type Pb-Zn sulfide deposit at Chah Gaz region, Sanandaj-Sirjan Zone, Kerman Province 101 120 29883 10.22108/ijp.2025.146146.1368 FA Azam Zahedi Assistant Professor, Department of Geology, Faculty of Sciences, University of Gonabad, Gonabad, Iran Mehrdad Karimi Assistant Professor, Department of Geology, Islamic Azad University Shiraz Branch, Shiraz, Iran 0000-0002-5954-450X Journal Article 2025 07 28 Introduction The Chah Gaz Pb-Zn ore deposit is an inactive mineralization located approximately 70 km southwest of Shahr-e Babak in Kerman Province, Iran. It lies within the geologically significant Sanandaj-Sirjan zone, a region renowned for its massive sulfide deposits and thus the focus of extensive previous research (Mousivand et al., 2007; Badrzadeh, 2009; Mousivand, 2011). Numerous consulting engineering companies have studied the Chah Gaz deposit in the past, primarily with an exploratory focus (Sabzehei and Afrooz, 1989; Kavoshgaran Co., 1990; Tehran Padir Co., 1991; Minook Co., 1993; Sabzehei et al., 1993). The most recent scientific research by Mousivand (2011) indicated that, based on a brine pool model, the Chah Gaz deposit closely resembles the siliciclastic felsic type or Bathurst-type deposits, such as those in the Bathurst mining district in Canada and the Iberian Pyrite Belt in Spain and Portugal. The deposit also shows strong geological similarities to volcano-sedimentary volcanogenic Kuroko deposits (Soleimani Alh-Dadi, 2017). Kuroko-type volcanogenic massive sulfide (VMS) deposits are significant submarine hydrothermal mineralizations formed in back-arc basins, associated with bimodal volcanic activity. They are key sources of base metals such as copper and zinc, characterized by low- to medium-temperature hydrothermal fluids and bimodal magmatism. These genetic features are essential for identifying exploration targets and understanding metallogenic processes in extensional tectonic settings (Ohmoto, 1996). The principal objectives of this study were to investigate the genesis of the deposit through an integrated approach, including geochemistry, petrography, trace element distribution, and fluid inclusion studies. Additionally, the Chah Gaz deposit is compared to global massive sulfide analogues based on key characteristics such as host rock sequences, mineral paragenesis, and tectono-magmatic setting. Method The concentrations of 23 trace elements and 14 rare earth elements were determined in the ore and metamorphic host rocks using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), conducted by ZarAzma Mineral Studies. Six ore samples were analyzed for gold content using Fire Assay and ICP methods. Eleven samples of ore and associated alteration rocks were examined via X-ray Diffraction (XRD) to identify major and minor minerals. Temperature-pressure measurements of fluid inclusions were carried out using a Linkam heating-cooling stage model THMSG600, TMS94, with a temperature range of -196 to +600 °C, equipped with a computer-linked simultaneous imaging system for video and slide recording. Results and Discussion Regional Geology The Chah Gaz Pb-Zn ore deposit is situated southwest of Shahr-e Babak, within the southern Sanandaj-Sirjan structural zone. This area comprises metamorphosed rocks such as slate, schist, metarhyolite, metabasalt, and gneiss. The gneisses are likely metamorphosed Cambrian granites transformed into orthogneisses. These rocks are metamorphosed to the greenschist facies and display diverse structures including boudinage, foliation, and mylonitization. The studied host rocks are mainly weakly to moderately metamorphosed and include semi-gneiss, schist, mineralized mylonite, quartzite, metarhyolite, and metabasalt. The schists exhibit chloritic and sericitic alteration, with chlorite contributing to preferred foliation. Black slates contain mica and quartz minerals with relatively weak foliation. Rhyolites in the area have been tectonically transformed into mylonites, showing secondary mineralization such as sericite and goethite veinlets, identified by XRD due to their fine grain size. Mineralization Both hypogene and supergene mineralization are present. Hypogene minerals include sphalerite, galena, pyrite, and chalcopyrite, while supergene minerals comprise covellite, chalcocite, smithsonite, cerussite, malachite, and iron oxides, especially in the oxidized zone. The gangue minerals mainly consist of sericite, quartz, chlorite, feldspar, siderite, ankerite, dolomite, and barite. Pyrite is the most abundant primary sulfide in the hypogene zone, occurring as euhedral, vein, and cataclastic forms, indicating intense deformation and metamorphic processes. Secondary pyrite appears rregular and veinlet-like, with iron oxide inclusions reflecting asynchronous sulfide and oxide phases. Chalcopyrite forms after pyrite as fracture-fillings, while sphalerite is a secondary sulfide enriched in zinc. Covellite is the dominant supergene oxidation mineral, formed by the alteration of chalcopyrite along its fractures. Azurite and malachite are observed in oxidized zones alongside goethite and limonite. Geochemistry The highest concentrations of major elements in the host rocks are silica, aluminum, iron, potassium, and magnesium. The elevated Al₂O₃ and LOI values in the host rocks are attributed to clay alteration, resulting from the formation of minerals rich in volatile components such as illite, halloysite, montmorillonite, and other hydrated minerals, consistent with XRD results. The highest average concentrations of minor elements include zinc (5.2 wt%), lead (4.1 wt%), copper (1.9 wt%), sulfur (9.5 wt%), calcium (0.06 wt%), and barium (3.6 wt%), indicating the abundance of sulfide minerals such as galena, sphalerite, chalcopyrite, and barite. The anomalous arsenic content in most ore samples suggests the presence of gold in the area. Fire assay analysis of six sulfide ore samples revealed an average gold content of 8 ppm, exceeding the economic threshold. In contrast, the silver content in the sulfide ore is significantly below the economic grade, with an average concentration of 0.003574 wt%, compared to the economic grade of 0.01 wt%. The absence of silver in this deposit may serve as an important indicator for determining the ore deposit type (Santagulda and Hannington, 1996; Tajeddin et al., 2019). Conclusion The Chah Gaz deposit represents a typical Kuroko-type volcanogenic massive sulfide system formed in a back-arc basin setting, characterized by acidic volcanic host rocks, stratiform to semi-massive sulfide mineralization, and a paragenetic sequence dominated by chalcopyrite, sphalerite, galena, and abundant barite. It contains economically significant lead, zinc, and copper, with gold concentrations reaching up to 8 ppm. The mineralizing fluids exhibit moderate salinities of 10–15 wt% NaCl and are associated with intense sericitic alteration. Unlike previous classifications as Bathurst-type, Chah Gaz differs by its higher gold -to -silver ratio (~1.4), moderate fluid salinity (vs. >25 wt% NaCl in Bathurst), dominance of sulfide minerals over sulfosalts, and a distinctive abundance of barite. These geological, geochemical, and mineralogical features support the reclassification of Chah Gaz as a Kuroko-type massive sulfide deposit. Introduction The Chah Gaz Pb-Zn ore deposit is an inactive mineralization located approximately 70 km southwest of Shahr-e Babak in Kerman Province, Iran. It lies within the geologically significant Sanandaj-Sirjan zone, a region renowned for its massive sulfide deposits and thus the focus of extensive previous research (Mousivand et al., 2007; Badrzadeh, 2009; Mousivand, 2011). Numerous consulting engineering companies have studied the Chah Gaz deposit in the past, primarily with an exploratory focus (Sabzehei and Afrooz, 1989; Kavoshgaran Co., 1990; Tehran Padir Co., 1991; Minook Co., 1993; Sabzehei et al., 1993). The most recent scientific research by Mousivand (2011) indicated that, based on a brine pool model, the Chah Gaz deposit closely resembles the siliciclastic felsic type or Bathurst-type deposits, such as those in the Bathurst mining district in Canada and the Iberian Pyrite Belt in Spain and Portugal. The deposit also shows strong geological similarities to volcano-sedimentary volcanogenic Kuroko deposits (Soleimani Alh-Dadi, 2017). Kuroko-type volcanogenic massive sulfide (VMS) deposits are significant submarine hydrothermal mineralizations formed in back-arc basins, associated with bimodal volcanic activity. They are key sources of base metals such as copper and zinc, characterized by low- to medium-temperature hydrothermal fluids and bimodal magmatism. These genetic features are essential for identifying exploration targets and understanding metallogenic processes in extensional tectonic settings (Ohmoto, 1996). The principal objectives of this study were to investigate the genesis of the deposit through an integrated approach, including geochemistry, petrography, trace element distribution, and fluid inclusion studies. Additionally, the Chah Gaz deposit is compared to global massive sulfide analogues based on key characteristics such as host rock sequences, mineral paragenesis, and tectono-magmatic setting. Method The concentrations of 23 trace elements and 14 rare earth elements were determined in the ore and metamorphic host rocks using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), conducted by ZarAzma Mineral Studies. Six ore samples were analyzed for gold content using Fire Assay and ICP methods. Eleven samples of ore and associated alteration rocks were examined via X-ray Diffraction (XRD) to identify major and minor minerals. Temperature-pressure measurements of fluid inclusions were carried out using a Linkam heating-cooling stage model THMSG600, TMS94, with a temperature range of -196 to +600 °C, equipped with a computer-linked simultaneous imaging system for video and slide recording. Results and Discussion Regional Geology The Chah Gaz Pb-Zn ore deposit is situated southwest of Shahr-e Babak, within the southern Sanandaj-Sirjan structural zone. This area comprises metamorphosed rocks such as slate, schist, metarhyolite, metabasalt, and gneiss. The gneisses are likely metamorphosed Cambrian granites transformed into orthogneisses. These rocks are metamorphosed to the greenschist facies and display diverse structures including boudinage, foliation, and mylonitization. The studied host rocks are mainly weakly to moderately metamorphosed and include semi-gneiss, schist, mineralized mylonite, quartzite, metarhyolite, and metabasalt. The schists exhibit chloritic and sericitic alteration, with chlorite contributing to preferred foliation. Black slates contain mica and quartz minerals with relatively weak foliation. Rhyolites in the area have been tectonically transformed into mylonites, showing secondary mineralization such as sericite and goethite veinlets, identified by XRD due to their fine grain size. Mineralization Both hypogene and supergene mineralization are present. Hypogene minerals include sphalerite, galena, pyrite, and chalcopyrite, while supergene minerals comprise covellite, chalcocite, smithsonite, cerussite, malachite, and iron oxides, especially in the oxidized zone. The gangue minerals mainly consist of sericite, quartz, chlorite, feldspar, siderite, ankerite, dolomite, and barite. Pyrite is the most abundant primary sulfide in the hypogene zone, occurring as euhedral, vein, and cataclastic forms, indicating intense deformation and metamorphic processes. Secondary pyrite appears rregular and veinlet-like, with iron oxide inclusions reflecting asynchronous sulfide and oxide phases. Chalcopyrite forms after pyrite as fracture-fillings, while sphalerite is a secondary sulfide enriched in zinc. Covellite is the dominant supergene oxidation mineral, formed by the alteration of chalcopyrite along its fractures. Azurite and malachite are observed in oxidized zones alongside goethite and limonite. Geochemistry The highest concentrations of major elements in the host rocks are silica, aluminum, iron, potassium, and magnesium. The elevated Al₂O₃ and LOI values in the host rocks are attributed to clay alteration, resulting from the formation of minerals rich in volatile components such as illite, halloysite, montmorillonite, and other hydrated minerals, consistent with XRD results. The highest average concentrations of minor elements include zinc (5.2 wt%), lead (4.1 wt%), copper (1.9 wt%), sulfur (9.5 wt%), calcium (0.06 wt%), and barium (3.6 wt%), indicating the abundance of sulfide minerals such as galena, sphalerite, chalcopyrite, and barite. The anomalous arsenic content in most ore samples suggests the presence of gold in the area. Fire assay analysis of six sulfide ore samples revealed an average gold content of 8 ppm, exceeding the economic threshold. In contrast, the silver content in the sulfide ore is significantly below the economic grade, with an average concentration of 0.003574 wt%, compared to the economic grade of 0.01 wt%. The absence of silver in this deposit may serve as an important indicator for determining the ore deposit type (Santagulda and Hannington, 1996; Tajeddin et al., 2019). Conclusion The Chah Gaz deposit represents a typical Kuroko-type volcanogenic massive sulfide system formed in a back-arc basin setting, characterized by acidic volcanic host rocks, stratiform to semi-massive sulfide mineralization, and a paragenetic sequence dominated by chalcopyrite, sphalerite, galena, and abundant barite. It contains economically significant lead, zinc, and copper, with gold concentrations reaching up to 8 ppm. The mineralizing fluids exhibit moderate salinities of 10–15 wt% NaCl and are associated with intense sericitic alteration. Unlike previous classifications as Bathurst-type, Chah Gaz differs by its higher gold -to -silver ratio (~1.4), moderate fluid salinity (vs. >25 wt% NaCl in Bathurst), dominance of sulfide minerals over sulfosalts, and a distinctive abundance of barite. These geological, geochemical, and mineralogical features support the reclassification of Chah Gaz as a Kuroko-type massive sulfide deposit.

https://ijp.ui.ac.ir/article_29883_d460c90aa7a05e3cb38802921d0c0777.pdf