Abstract

The west-central volcanic mineral belt of Iran, Urumieh-Dokhtar Magmatic Arc (UDMA) which forms part of the principal metalliferous Tethyan belt stretching >2000-km-long and 100-km-wide, hosts some of the world-class porphyry copper and several epithermal gold-silver deposits similar to those found in the Andes. The Chah-Zard Ag-Au epithermal deposit is located in central part of the UDMA. The country rocks form a circular-shaped volcanic complex consisting of poorly sorted-polymictic clast-supported volcanic breccias hosted in altered Miocene (6.24 Ma) intermediate to felsic volcano-plutonic units (andesite, trachy-andesite, dacite, porphyritic dacite, porphyritic rhyolite). The alteration assemblages are quartz, illite-pyrophyllite, K-feldspar, sericite and jarosite occurring in an area greater than 9 km². The mineralization at Chah-Zard is directly related to the intensity of silicification and hosted in sulphide-cemented breccia; and gold-bearing quartz-sulphide-gypsum veins are accompanied by illite-pyrophyllite and jarosite alterations. Samples collected from trenches and diamond drill holes show up to 21 g/t Au and 92 g/t Ag and 66 g/t Au and 463 g/t Ag, respectively. Ore minerals are pyrite, arsenical pyrite, chalcopyrite, galena, sphalerite, native gold, Ag-tetrahedrite, Ag-tennantite, chalcocite, arsenopyrite, marcasite, sulfosalts and bornite. The major associated gangue minerals are quartz, gypsum and jarosite. Based on intensity of silicification, argillic  and jarosite alterations with sulphides and gypsum as clasts’ cement in the gold-bearing veins, it is likely that the Chah-Zard deposit could be an overprinting system of low-sulphidation to high-sulphidation Ag-Au epithermal mineralization, making it as a model for exploration of similar deposits in the Tethyan belt. Further mineralogical-textural studies are in progress to fully understand the ore-forming processes.