The Mineral chemistry and Geothermometry of Sphalerite and Galena in Changoreh epithermal deposit, NW of Takestan: implication to type of mineralization

The study area is located about 25 km northwest of Takestan city, within Tarom-e-Sofla metallogenic belt. This area is covered by a widespread Eocene andesite to dasite volcanic rocks affected by Oligo-Miocene monzogranite to granodiorite igneous bodies which altered them to silicic, argillic zones as long as hypogene sulfide vein-veinlet mineralization (e.g. galena, sphalerite, pyrite, rare chalcopyrite and tetrahedrie- tennantite) occurred along with supergene minerals (e.g anglesite, cerussite, malachite, covellite and goethite in oxide zone). This study concentrated on geochemistry and geo-barometry of sphalerite and galena to evaluate sulfidation state, temperature and type of ore formation. During mineralography studies, two types of galena were recognized: 1) high temperature, brecciated veinlet type including tetrahedrite and, 2) low temperature coarse grained type along with colloform sphalerite. Based upon mineral chemistry of sphalerite, average concentration of Cd, Ga, Ge, Zn/Cd and Ga/Ge ratios were 5870, 970, 1380, 165.4 and 1.39, respectively. Ga/Ge ratios of sphalerites geothermometry indicate that the formation temperatures of sphalerite are between 170°C and 220°C. The amount of log aS2 hydrothermal fluid (-11.5 to -13.5), calculated from FeS content (0.33-0.80 mol%) in sphalerite, can be attributed to moderate sulfidation state for changoreh deposit. According to Sb/Bi in galena geo-thermometer, geochemistry of sphalerite (low ∑Sred activites, moderate Cd content (5870 ppm) and average Zn/Cd ratio (165.4), physico-chemical and thermodynamics of ore-bearing fluid in Changoreh is in accordance with moderate to high temperature epithermal deposits.