Solid-state diffusion in sphalerites: an experimental verification of the "chalcopyrite disease"

The zonation, exsolution and replacement phenomena occurring in natural sphalerites and known as the «chalcopyrite disease» were experimentally simulated by solid-state diffusion studies using (Zn,Fe)S crystals as receptors and CuInS 2 , CuFeS 2 , Cu 5 FeS 4 , Cu 2−x S and CuS as metal sources, at temperatures between 400 and 750°C. Therefore, the expression «diffusion-induced segregations» (DIS) is proposed instead of «disease». The driving force for the diffusion is a chemical-potential gradient between the sphalerite crystal (receptor) and the surrounding sulphide powders (diffusion source). Diffusion coefficients of (Cu + In) in ZnS were experimentally determined. The nature of the DIS phases (intermediate solid solution, chalcopyrite, bornite, digenite) and the corresponding textures (dusty, blebs, worm-like, water-melon) depend on the Fe content of the sphalerite, time, temperature, Cu:Fe ratio in the diffusion source, and the sulphur fugacity. General rules for DIS phenomena are deduced from the experimental results and compared to natural occurrences. All the natural «disease» textures of Cu-rich phases in sphalerite can be reproduced by our experiments