Geochemical, isotopic, and fluid inclusion signatures of Zn-Pb mineralization in the Tiran mining district, Isfahan, Sanandaj-Sirjan zone (Iran)

Abstract

In Tiran base-metal district, the post-Early Cretaceous epigenetic Zn-Pb deposits occur as fault-controlled pocket-like lenses. The main structural feature of mineralization is its association with a district-scale strike-slip fault, which cuts an en-echelon folded terrane. Mineralization occurs as sphalerite, galena, pyrite, and minor chalcopyrite found within massive ore, breccia textures, veins and veinlets, disseminated grains and carbonate replacements along tectonized limestone-shale contacts. The cumulative reserves of this district is 10 Mt grading at 6% Zn + Pb. Host rock silicification and calcitization formed during hydrothermal alteration. Fluid inclusion data revealed that ore minerals precipitated due to the mixing of two fluids, one determined from sphalerite-hosted inclusions (Homogenization temperature: 155 °C and salinity: 19 wt% NaClequiv.) and the other observed in quartz inclusions (Th: 184.5 °C and salinity: 12.5 wt% NaClequiv.). The sulfur isotope compositions of sulfide minerals vary between −8.92 and +4.15‰ and ranged from 22.61 to 23.88‰ for barite, thus suggesting an Early Tertiary marine sulfate influence. Sulfur isotopic data favor two sources of sulfur: bacteriogenic activity (δ34SCDT −9 to −6‰) and thermochemical sulfate reduction (δ34S: −1 to +4‰). The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.1–18.4, 15.6–15.7, and 38.4–38.6, respectively) reflect upper crustal basement rocks as the source of metals. Fertile ore fluids mixed within fault zones, along the contacts of limestone and shale. Base metal deposition during fluid mixing could be a result of increasing reduced sulfur, cooling, and decreasing ligand activity after tectonic movements. The multiple lines of evidence presented here are consistent with the mineralization in the Tiran mining district being similar to Mississippi Valley-type deposits.