Fluid inclusion, mineralogical, geochemical, and isotopic (O, S) evidence for the genesis of the Khan-Khatun Zn-Pb deposit, Tabas Block, Iran

Abstract

The Khan-Khatun ZnPb deposit is located in the southeast margin of the Tabas Block of the Central Iranian Microcontinent. The stratabound ZnPb mineralization is of epigenetic origin and hosted by the Late Cretaceous limestones. The ore deposition occurred in structural open spaces and much less as a disseminated replacement in carbonate rocks. The deposit consists of sulfide and non-sulfide base metal ore types. Sulfide ores include sphalerite, galena, and minor amounts of pyrite and chalcopyrite. Three paragenetic stages are recognized: pre-, hydrothermal, and supergene mineralization. Fine-grained pyrite and chalcopyrite (0.02 to 0.15 mm) precipitated during the early stages of hydrothermal mineralization. Galena formed with or sometimes after sphalerite. The δ³⁴S values of sphalerite and galena range from +10.4 ‰ to +13.7 ‰ and + 10.2 ‰ to +14.1 ‰, respectively, and are consistent with thermochemical sulfate reduction (TSR) of the Jurassic evaporites. Willemite is an abundant non-sulfide mineral characterized by red-brown to white colors. The red-brown willemite formed during the late stages of the hydrothermal mineralization. The δ¹⁸O values of red-brown and white-colored willemite vary from +14.3 to +16.1 ‰ and − 9.62 to −8.1 ‰, respectively. Differences in δ¹⁸O values between red-brown willemite and white-colored willemite are probably the result of hydrothermal and supergene processes. Homogenization temperatures of primary fluid inclusions in calcite coexisting with sulfide ores and red-brown willemite range from 110 to 210 °C and 112 to 177 °C, respectively. The salinities of aqueous fluid inclusions of calcite and red-brown willemite vary from 11.1 to 21.26 wt% NaCl equiv. and 10.61 to 16.15 wt% NaCl equiv., respectively. Microthermometric measurements, isotopic analyses, geochemical, mineralogical, and textural evidence indicate that the mineralization process at the Khan-Khatun ZnPb deposit is consistent with Mississippi Valley-type (MVT) deposits.