Formation of nano-CdS solid solution: A mechanism for Cd enrichment in sphalerite

The occurrence and mechanisms behind the supernormal enrichment of dispersed elements in sphalerite remain controversial. In this study, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and scanning transmission electron microscopy (STEM) were employed to investigate the occurrence state and enrichment mechanism of cadmium (Cd) in Cd-rich sphalerite from the Jinding deposit. In regions with relatively low Cd concentrations (∼4000 to 10 000 ppm), Cd was observed to substitute for Zn within the sphalerite lattice. However, in regions with high Cd concentrations (exceeding 30 000 ppm), a novel nanoscale occurrence state of Cd was identified, specifically as a nano-CdS solid solution. This finding provides new nanoscale mineralogical evidence to refine the understanding of the supernormal enrichment process of Cd in sphalerite. The enrichment of Cd is driven by mechanisms such as reactivation and dynamic recrystallization induced by plastic deformation in sphalerite, as well as solid solution precipitation during cooling. A coherent interface relationship between CdS and ZnS plays a critical role in the formation and stabilization of the nano-CdS solid solution. The formation of such nano solid solutions may represent a potential mechanism for the supernormal enrichment of dispersed elements, offering new insights into the complex distribution characteristics of these elements at the micrometer scale.