Platinum-group elements and gold distribution in ores of the Haftcheshmeh porphyry Cu-Mo-Au deposit, NW Iran

Abstract

The Haftcheshmeh porphyry Cu-Mo-Au deposit is located in the Arasbaran metallogenic belt, northwest Iran, with mineralization occurring mainly in gabbro-diorite and granodiorite porphyry. Pyrite and chalcopyrite are the most abundant sulfides that occur as disseminated and veinlet type ores in the potassic alteration zone. Platinum-group elements (PGEs), Au, and Cu concentrations of selected pyrite- and chalcopyrite-bearing samples were analyzed using in situ LA-ICP-MS and bulk rock Lead Fire Assay. Relatively high contents of PGEs and other precious elements are present in sulfide minerals, especially in pyrite that is the principal carrier of these elements in the deposit. Palladium is the most abundant of the PGEs in the sulfides. The contents of Pd are systematically higher than Pt in this deposit, consistent with other porphyry deposits, although Os, Rh, and Ir abundances are in general equal to or below the limits of detection in pyrite and chalcopyrite. The most important factors related to potential PGEs and chalcophile elements enrichment in the Haftcheshmeh deposit is the oxidized mafic endmember components of source magmas, i.e., high ƒO2 conditions, possibly with a semi-metal collector melt involved, and the high saline magmatic hydrothermal fractionation process. All these mechanisms seem to have enhanced the concentration of PGEs, Au, and other chalcophile metals. PGEs and other chalcophile elements were transported by exsolved high-T, saline magmatic hydrothermal fluids and then low T reaction and reduction to enhance saturation of sulfide phases during mineralization associated with potassic alteration.