The enrichment mechanism of indium in Fe-enriched sphalerite from the Bainiuchang Zn-Sn polymetallic deposit, SW China

Abstract

Dispersed metals, such as indium and cadmium, are widely used in certain high-tech applications and are important resources for world economies. Sphalerite is an important host mineral for indium, cadmium and other trace elements which can record genetic information in hydrothermal systems. The Bainiuchang Zn-Sn polymetallic deposit, located in the southwest margin of the Yangtze Block, has substantial zinc concentrates with indium and cadmium mineralization. In this study, we examined different sphalerite grains from this deposit with elemental mapping, in-situ trace element geochemistry and S-Pb isotopic composition. The discrepancy of indium and Zn/Cd ratio suggest that there are at least two generations of sphalerite. The mineralization of indium is mainly enriched in marmatite [(Zn,Fe)S)] from cassiterite-bearing ore, rather than in that from cassiterite-poor ore. The mineralization of cadmium occurred in all types of ore. The relevance of trace elements suggests that indium can be incorporated into sphalerite by a couple substitution of (In, Ga)3+ + (Cu, Ag)+ ↔ 3(Zn, Fe)2+, whereas Fe, Cd can be incorporated into sphalerite by substitutions of Fe2+ ↔ Zn2+ and Cd2+ ↔ Fe2+. Sulfur (δ34SV-CDT =+2.43 to +3.88 ‰) and lead (206Pb/204Pb = 18.346–18.396, 207Pb/204Pb = 15.675–15.691) isotopic compositions indirectly suggest that indium and cadmium in the Bainiuchang Zn-Sn polymetallic deposit may be sourced from magmatic-hydrothermal fluids associated with Late-Cretaceous magmatic activities in this district.