Chalcopyrite has been milled for up to 50 h in oxygen, air and argon atmospheres using a laboratory ball mill. No phase changes were evident in argon but the XRD peaks were weaker and broader indicating crystalline refinement. In oxygen, even after I h milling peaks for CuSO4 center dot 5H(2)O were present and these became predominant after 20 h milling where the chalcopyrite peaks were absent. In air, partial oxidation to CuSO4 center dot 5H(2)O was evident after 50 h. Leaching of the resultant powders with water showed 80% dissolution after 50 It milling in oxygen, significantly greater than the 20% and 6% dissolution after milling for 50 It in air and argon respectively. Solution analyses showed the Cu/Fe ratio increased with milling time in oxygen suggesting selectivity may be possible. The insoluble residue was found to consist of haematite, elemental sulphur and unreacted chalcopyrite. (c) 2005 Elsevier B.V. All rights reserved.