Thermodynamic simulation on indium enrichment condition in the Huangshaping skarn Zn-Pb system (South China)

Indium, crucial for emerging industries like optoelectronics, is a strategic metal linked to national prosperity and defense. However, understanding its enrichment during migration-precipitation in skarn-type Zn-Pb deposits is limited. This study focuses on the Huangshaping Zn-Pb deposit in the Nanling belt, China, which is a skarn-type deposit with quartz porphyry as the ore-causative intrusion. Through petrography, mineralization was identified as skarn, oxide, and sulfide stages, with three sphalerite types (Sp1, Sp2a, Sp2b). EPMA and LA-ICP-MS analyses revealed different indium concentrations, with Sp1 being the most enriched (mean = 134.54 ppm). LA-ICP-MS mapping showed that Sp1 is rich in In, Cu, and Sn. Mineral paragenesis combined with GGIMFis thermometer for sphalerite trace elements and thermodynamic calculations indicate indium-rich sphalerite precipitates under weakly acidic pH 4.5–6.0, high oxygen fugacity (logfO₂ = –32.2 to −29.7), high temperature (201–316 °C), and high sulfur fugacity (logfS₂ = −13.42 to −7.11) in a reduced, H₂S-rich environment. We propose that in skarn systems, the enrichment of indium occurs during the early stages of sphalerite crystallization, specifically at high temperatures. This enrichment process occurs in a fluid environment characterized by a weakly acidic pH, high oxygen fugacity, and high sulfur fugacity. The findings deepen our understanding on indium enrichment and the physicochemical conditions in skarn-type Zn-Pb systems and may aid prospecting in similar deposits.