XPS, Fe Lalpha,beta and Cu Lalpha,beta X-ray emission and Fe L-, Cu L-, S L-edge and O K-edge absorption spectroscopies, Mossbauer spectroscopy and cyclic voltammetry were applied to study reacted surface layers of natural chalcopyrite, CuFeS2. The surfaces became metal-depleted after the anodic oxidation in 1 M HCl and the leaching in 1 M H2SO4 + 0.2 M Fe-2(SO4)(3) or 1 M HCl + 0.4 M FeCl3 solutions, with the sulfur excess and iron/copper ratio been higher in the last instance, and were enriched in copper after the electrochemical reduction. The electronic structures of the metal-deficient layers up to several tenths of micrometer thick were similar to that of chalcopyrite, except that the density of the highest occupied states depended on sulfur anions formed (predominant S-3-anions after the ferric sulfate treatment, S-4-anions after the ferric chloride leaching or the potential sweep to 0.9 V, etc.). The layers created by the preliminary oxidation had only a small effect on the chalcopyrite voltammetry. We suggest a new reaction mechanism considering a role of the surface changes, including disordering and Anderson localization of the electronic states. (C) 2003 Elsevier B.V. All rights reserved.