Mineralization and genesis of the Pb-Zn(-Cu) non-sulfide ore in Chah Mileh deposit (NE Anarak), Central Iran

The Chah Mileh Pb-Zn (-Cu) deposit is located in the Yazd-Anarak metallogenic belt, Central Iran. Primary sulfide mineralization (e.g., galena, sphalerite, chalcopyrite and pyrite) formed within dolomitic marble unit of the Middle Triassic Chah Gorbeh complex. Mineral matter often occurs as, brecciaed, open-space filling, disseminated and replacement textures. The non-sulfide ore of the Chah Mileh deposit were formed by supergene oxidation of primary sulfide minerals during the complex interplay of tectonic uplift, karst development, changes in the water table, and weathering. Cerussite, hemimorphite, wulfenite, mimetite, smithsonite, malachite and iron oxy-hydroxides are the most non-sulfide ore minerals in the Chah Mileh deposit. In Chah Mileh deposit, the oxidation of pyrite and similar sulphides led to supply of sulphuric acid which resulting low-pH values and increasing PCO2 due to acid-neutralisation by host-rock carbonates; therefore liberation of sulphate ions and precipitation of iron oxy-hydroxides play an important role in the formation of non-sulphide ore. Under acidic conditions most of the zinc leaves the oxidation zone and precipitates as zinc carbonates (e.g., smithsonite and less hydrozincite, based on PCO2 values) in adjacent to the carbonate host rock, while most of the lead within the oxidation zone precipitates as cerussite and adsorbed by feoxyhydroxides. Based on geological, textural and mineralogical composition, the non-sulfide ore of the Chah Mileh belongs to supergene non-sulfide deposits and subtype of direct replacement deposits (red ore).