Raman spectroscopic investigations have been carried out on the oxidation, utilising ferric ion or potential control, of chalcopyrite in chloride and sulfate media. In chloride solutions the rate of oxidation was sufficient for the in situ examination of products, and elemental sulfur was found to develop heterogeneously on the mineral surface. The formation of an accompanying, Raman-inactive, phase was demonstrated from the appearance of additional Raman bands after irradiation of the oxidised surface with 442 nm light. The photo-induced product yielded a Raman spectrum consistent with polymeric sulfur and it is concluded that the parent compound is a metal-deficient sulfide having a remnant chalcopyrite lattice structure. This remnant phase was metastable at room temperature, decomposing relatively rapidly at temperatures >70 ?C. Thiosulfate and other polythionate ions were not detected at the surface, nor were jarositic phases. There was little evidence for the formation of polysulfides. Chalcopyrite reacted slowly in sulfate solutions. Ex situ investigations in such media showed that similar products were observed as in chloride, although at a much slower rate and with less relaxation of the oxidised remnant lattice.