Substitution of In and Cu for Zn in wurtzite and sphalerite with implications for ore genesis: Insights from ab initio calculations and molecular dynamics simulations

Indium (In) is a critical metal with strategic resource significance. In the context of natural mineralization, In mainly accumulates in zinc sulfide (i.e. ZnS) through isomorphous substitution, owing to its sulfur-philic properties. ZnS crystallizes in close-packed structures, the most common of which are (3-ZnS (i.e. sphalerite) with cubic 3C structures and its polymorph alpha-ZnS (i.e. wurtzite) with hexagonal 2H structures. However, little is known about the physicochemical constraints on these two crystal structures, which hinders the understanding of In mineralization. Therefore, it is crucial to investigate the controlling role of the two crystal structures in the enrichment mechanism of In within ZnS. In this contribution, we employed ab initio calculations and molecular dynamics simulations to study the thermodynamic properties, electronic structures, and bond populations of Inbearing wurtzite and In-bearing sphalerite that are formed by the mechanism Cu++In3+-> 2Zn2+. The results show that: (1) At low temperatures, In is more likely to enter sphalerite, whereas at high temperatures, it tends to accumulate in wurtzite; (2) Sphalerite exhibits a narrower band gap, resulting in more pronounced electronic properties and enhanced electronic transitions compared to wurtzite; and (3) The Gibbs free energy and bond population indicate that In-bearing sphalerite is more stable than In-bearing wurtzite. This suggests that during the later ore-forming stages in magmatic-hydrothermal deposits, In-bearing wurtzite undergoes a phase transformation and converts into In-bearing sphalerite as the temperature decreases. This study provides deep insights into the mineralization mechanisms of In-rich deposits and the distribution patterns of In within the ore.