Distribution of indium and gallium in sphalerite from skarn and hydrothermal vein deposits in the Hwanggangri mineralized district, South Korea

Abstract

The geochemistry of sphalerite from seven metallic ore deposits in the Hwanggangri mineralized district in South Korea was studied, with a special focus on the concentrations of In and Ga. The chemical compositions were analyzed using laser ablation-inductively coupled plasma-mass spectroscopy and compared based on deposit type (skarn and hydrothermal vein) and ore species (W, Mo, Zn–Pb, and W–Zn–Pb). In hydrothermal W and W–Zn–Pb vein deposits, In was highly concentrated, with averages of up to 696 ppm, whereas Mo and Zn–Pb skarn deposits produced low concentrations below 43 ppm on average. In contrast, the Ga concentrations were quite low throughout the deposits and did not exceed 16 ppm on average. Indium showed a clear positive correlation with Cu and was strongly associated with the development of chalcopyrite-disease, with Ag and Sn potentially playing subordinate roles in the substitution. The binary correlations between trace elements suggested that principal coupled substitutions, such as 3Zn2+ ↔ 2(Cu, Ag)+ + Sn4+ and 2Zn2+ ↔ Cu+ + In3+, prevailed in In-bearing sphalerite. A discernable weak positive correlation is observed between In and Cd, mostly in the W-bearing deposits, implying that Cd, a common constituent in sphalerite, could be used as an exploration proxy in some cases. The general tendency of high In and low Ga concentrations in the sphalerites from the Hwanggangri mineralized district indicates relatively high temperature of mineralizing fluids, generally above 250 °C, which favored the prevalence of In-chloride complexes over Ga-hydroxide complexes. Additionally, the In enrichment in the hydrothermal vein ores rather than the skarn ores emphasizes the importance of the direct contribution of magmatic fluids to ore mineralization under high temperature conditions with little influence from the host rock.