Mineralogy of indium mineralization in the Dajing Sn-Cu polymetallic deposit in Inner Mongolia

Abstract

The Great Xing’an Sn-polymetallic metallogenic belt in Inner Mongolia is a potential district for indium (In) resources, where In mineralization has been discovered in the Dajing Sn-Cu polymetallic deposit, but the occurrence of In is not well understood. In this contribution, detailed mineralogical investigations of In-bearing minerals in the Dajing Sn-Cu deposit were conducted, based on fieldwork and ore petrography, combined with whole-rock analysis, EPMA, and LA-ICP-MS. Three ore-forming stages and six types of sphalerite are distinguished. The highest In content (average 0.18 wt%) is observed in earlier exsolved sphalerite (Ia) in the Cu-Sn stage, other types of sphalerite contain relatively lower In concentration, with the average value ranging from 16 to 478 ppm. Overall, sphalerite in the Cu-Sn stage is more enriching in In than that in the Pb-Zn stage. Indium mainly occurs as solid solution in sphalerite. Other minerals such as stannite and chalcopyrite (Ia) exhibit relatively elevated In concentration (average >202 ppm). Cassiterite, pyrite, and pyrrhotite show negligible In content typically below 10 ppm. Combined with previous studies on ore-forming fluids, indium mineralization in the Dajing deposit is mainly associated with early-stage Cu-Sn fluids. The enrichment of In in sphalerite is probably attributed to the migration and diffusion of In in the Cu-Sn fluid during high-temperature conditions. Local dynamic processes (exsolution, diffusion, etc.) possibly have facilitated In mineralization in sphalerite. This study reveals the occurrence and distribution patterns of In in the Dajing deposit, promotes the recovery and utilization of In resources, and proposes new insights into the enrichment mechanisms and potential assessment of In.