The Emarat and Muchan sedimentary rock-hosted stratabound Zn-Pb deposits: New data and genetic implications

The Emarat and Muchan zinc-lead ore deposits are located in southwest of Arak within the middle part of the Malayer-Esfahan belt. These deposits have formed as stratabound within carbonate strata of Lower Cretaceous. Mineralization in these deposits is mainly open space filling, which consists of sphalerite, galena, pyrite and minor quantities of chalcopyrite associated with host rock silicification. The most abundant sulfide mineral is sphalerite, which occurs in two generations. Galena as an accessory mineral has been formed during and after formation of sphalerite. Based on textural evidence, silicification occurs in two separate stages. First, microcrystalline quartz replaces nearly all the original carbonate host rock. During the second stage, the vugs and fissures of the silicifed host rock were filled with macrocrystalline quartz associated with mineralization. The sulfur isotopic data indicated the δ34S values of sulfide minerals varies from +4.8 to +11.8 per mil. Based on these results, the Lower Cretaceous seawater acted most likely as the source of sulfide mineralization. The isotopic temperatures from two sphalerite-galena pairs at Emarat deposit varied from 121.1˚C in stage I to 112.8˚C in stage II, which are lower than the isotopic temperature of the Muchan deposit (134.3˚C). Combination of geological, mineralogical and sulfur isotope results suggest that connate water, metals and silica have been derived from diagenesis of Jurassic shales and sandstones. Furthermore, thermochemical sulfate reduction, interaction of the ore fluids with the host rock, and cooling were proposed to be the main ore depositional mechanisms.