High $${f_{{{\rm{H}}_2} - }}{f_{{{\rm{S}}_2}}}$$ Conditions Associated with Sphalerite in Latala Epithermal Base and Precious Metal Deposit, Central Iran: Implications for the Composition and Genesis Conditions of Sphalerite

Abstract

This paper presents the properties of fluid inclusions found in sphalerite from Latala epithermal base and precious metal deposit (Central Iran), which is hosted in Cenozoic volcanic-sedimentary host-rocks. The Latala Deposit represents an example of vein type, base metal deposits in the Miduk porphyry copper deposits (PCDs) in southern Urumieh-Dokhtar magmatic belt (UDMB). Mineralization in Latala epithermal base and precious metal vein type formed in 3 stages and sphalerite-quartz veins occur in stages 2 and 3. Stage 2 quartz-sphalerite veins are associated with chalcopyrite and zoned sphalerite, along with quartz+hematite, and Stage 3 quartz-sphalerite veins contain galena+sphalerite+ chalcopyrite and quartz with overgrowth of calcite. Mineralization in Stage 3 occurs as replacement bodies and contains Fe-poor sphalerite without zoning in the outer parts of the deposit. This paper focuses on fluid inclusions in veins bearing sphalerite and quartz. The fluid inclusion homogenization temperatures and salinity in sphalerite (some with typical zoning) range from 144 to 285 °C and from 0.2 wt.% to 7.6 wt.% NaCl eq. Sphalerite and fluid inclusions of the Latala base and precious metal deposit formed from relatively low-T and low-salinity solutions. Raman spectroscopy analyses indicate a high percentage of CO2 in the gas phase of fluid inclusions in Fe-poor sphalerites, as expected with melting temperature for CO2 of −56.6 °C, and significant amounts of H2. Lack of reduced carbon species (methane and lighter hydrocarbons) was confirmed in the petrographic study using UV light and Raman spectroscopy. High amounts of H2 in fluid inclusions of Fe-poor sphalerite can be the result of different intensities of alteration and diffusion processes. The common occurrences of CO2 in fluid inclusions have originated from magma degassing and dissolution of carbonates. The δ34S values for sulfide minerals in galena of sphalerite bearing veins vary between −9.8‰ and −1.0‰, and the δ34S values calculated for H2S are between −7.1‰ and +0.6‰. These values correspond to magmatic sulfur whit possible interaction with wall rocks. Magmatic fluids were successively diluted during cooling and continuous ascent. Secondary boiling would lead to variable amounts of potassic or prophylactic alteration and the hydrogen diffusion into the inclusions hosted in sphalerite of Latala.