Characteristics and genesis of the Ahangaran Pb Cu deposit Iran

The Ahangaran Pb(Cu) deposit is located in the Sanandaj-Sirjan metamorphic zone of the Zagros orogenic belt, a Cenozoic continental collisional zone between Arabian(south) and Iran(north) blocks. The deposit is hosted in Lower Cretaceous dolomitic limestone and has conformable and lenticular orebodies and bed-crosscutting ore veins. Pre-ore stage of minerals are fine-grained quartz, and ore stage of minerals are composed of dolomite, barite, calcite, coarse-grained quartz, galena, chalcopyrite, pyrite, and tetrahedrite. The study of the fluid inclusions shows that the ore fluids are a Cl^--Na⁺-Ca²⁺-Mg²⁺ system, with homogenization temperatures from 108℃ to 210℃ and the salinities from 7%NaCl eq to 29%NaCl eq. Combined with data of C-H-O isotopes from ore stage hydrothermal gangue minerals and associated fluid inclusions, the authors hold that the ore fluids were mainly derived from basinal brine, with or without contribution from magmatic fluids. The mineralization process led to the dissolution of the host carbonate. The δ³⁴S values of barite range from 18.7‰ to 22.7‰, and sulfides range from -3.1‰ to 9.7‰, suggesting that the reduced sulfur was probably the result of biological sulfate reduction(BSR). But this does not exclude the probable contribution of reduced sulfur from thermochemical sulfate reduction(TSR). The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of galena are 18.4083~18.454, 15.6512~15.6548, and 38.5628~38.5515, respectively, which are similar to those of the other Pb-Zn deposits in this region, i.e., the Malayer-Esfahan carbonated-hosted Pb-Zn metallogenic belt. It is suggested that their metals were derived from the same upper crustal rocks. Although the Ahangaran deposit shares some similarities with Mississippi Valley-type(MVT) deposits, the enrichment of ore stage quartz and copper sulfides suggests that the deposit may be classified as a magmatic-related carbonate-replacement-type deposit.