Supernormal enrichment of cadmium in sphalerite via coupled dissolution-reprecipitation process

Supernormal enrichment of cadmium in sphalerite is frequently observed in some sedimentary-hosted zinc-lead deposits, although related fluid process remains unconstrained. At the Jinding Mississippi Valley-type deposit, a considerable portion of cadmium has been remobilized from early sphalerite through coupled dissolution-reprecipitation reaction to form high-grade ores. Here we report natural occurrence of various sulfide nanoparticles and related textures in sphalerite that help document this process. A nanoscale study by transmission electron microscopy provides a rare glimpse of phase transition of cadmium from lattice-bond impurity, composition anomaly along planar defects, aggregates of hexagonal cadmium sulfide nanoparticles, to crystalline greenockite inclusions. Such a process may be mediated by oxidative dissolution on early-formed cadmiferous sphalerite during injection of cadmium-rich oxidative acidic fluids. This study provides an alternative mechanism versus exclusively solid-state diffusion for dispersed elements' redistribution in hydrothermal ore deposits. It also sheds light on artificial synthesis of II-VI semiconductor nanomaterials by similar methods. Coupled dissolution-reprecipitation allows Cd-rich fluids to react with sphalerite along lattice defects and in porous cores to form supernormal Cd enrichment, according to micro and nano-scale observations of samples from the Jinding deposit, SW China