Emarat carbonate-hosted Zn-Pb deposit, Markazi Province, Iran: A geological, mineralogical and isotopic (S, Pb) study

摘要

The Emarat deposit, with a total proved reserve of 10 Mt ore grading 6% Zn and 2.26% Pb, is one of the largest Zn-Pb deposits in the Malayer-Esfahan belt. The mineralization is stratabound and restricted to Early Cretaceous limestones and dolomites. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz, and dolomite. Textural evidence shows that the ore has replaced the host rocks and thus is epigenetic.rnSulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from Cretaceous sea-water through thermochemical sulfate reduction. Sulfur isotope compositions of four apparently copre-cipitated sphalerite-galena pairs suggest their precipitation was under equilibrium conditions. The sulfur isotopic fractionation observed for the sphalerite-galena pairs corresponds to formation temperatures between 77 ℃ and 168 ℃, which agree with homogenization temperatures of fluid inclusions.rnLead-isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high ~(238)U/~(204)Pb and ~(232)Th/~(204)Pb ratios. Ages derived from the Pb-isotope model give meaningless ages, ranging from Early Carboniferous to future. It is probable that the Pb-isotope model ages that point to an earlier origin than the Early Cretaceous host rocks are derived from older reservoirs in the underlying Carboniferous or Jurassic units, either from the host rocks or from earlier-formed ore deposits within these units.rnThis research and other available data show that the Emarat Zn-Pb deposit has many important features of Mississippi Valley-type (MVT) lead-zinc deposits and thus we argue that it is an MVT-type ore deposit.