The Zn-Pb sulfide and Pb-Zn-Ag non-sulfide Kuh-e-Surmeh ore deposit, Zagros Belt, Iran: Geologic, mineralogical, geochemical, and S isotopic constraints

Abstract

The carbonate-hosted Kuh-e-Surmeh deposit is located in the Zagros Simply Folded Belt, southwestern Iran. The semi-conformable tabular–like ore body lies within the northern flank of the NW–trending Kuh-e-Surmeh anticline. It is comprised of sulfide and non-sulfide base-metal ore types. The sulfide ore has a simple mineralogy and consists almost entirely of sphalerite, galena, and pyrite. Sphalerite is the main sulfide mineral having both crystalline and colloform texture. The Fe content of the sphalerite ranges between 0.04 and 8.9 wt% with the dark sphalerite zones containing higher (3.37–8.9 wt%) Fe values. Crystalline sphalerite is the main source of Ag in the sulfide ore. Galena formed simultaneously with and after sphalerite mineralization. The precipitation of pyrite occurred during the pre- to late sulfide ore mineralization phases. Anglesite is the most abundant non-sulfide mineral. Gray-colored, massive anglesite contains >100 ppm Ag, representing the main host of Ag mobilized during supergene events. On the basis geochemical data, in non-sulfide portion, there is an increase in Ag values with increasing Pb contents, independent of depth.The sulfur isotope enrichment factor (εSO4–primary sulfide minerals = 7.8‰) reflects the SO4−2 of the late stage gypsum formed by sulfate generated from the dissolution of primary sulfate minerals that mixed with sulfate originating from the oxidation and dissolution of sulfide minerals. Topographic relief, tectonic fracture systems, reactivation of the Surmeh Fault, and uplift related to the Zagros Orogeny all favored the establishment of arid climate conditions, providing an ideal environment for converting Zn-Pb sulfide ore to Pb-Zn-Ag non-sulfide ore.