Mechanochemical reactions are those which are initiated by the application of a mechanical force, In recent times it has been shown that solid state mechanochemical reactions can be initiated by milling the reactants in a high energy ball mill - a process known as mechanical milling. Oxidation/reduction reactions have been shown to occur at room temperature during mechanical milling, and this has led to the idea that it may be possible to refine metallic ores via room temperature mechanochemical processes, In this study, it has been found that pyrite (FeS2) can be mechanochemically processed in a high energy ball mill. Pyrite is the most common sulfide host for gold and in refractory pyrite samples gold is encapsulated in the pyrite matrix, so this matrix must be broken down prior to cyanidation. X-ray diffraction, Mossbauer spectroscopy and thermal analysis techniques have shown that pyrite can be oxidised mechanochemically, with the sulfur retained as a sulfate without the production of sulfur dioxide gas, Potential exists for this process to form the basis for an economically viable, environmentally friendly process for the treatment of refractory pyritic gold ores. (C) 1997 Elsevier Science Ltd.