A commercial enargite concentrate was mechanically milled in inert and oxidising atmospheres for 10 hours. No substantial effect was observed in either an inert atmosphere or in air other than a broadening and weakening of the diffraction peaks. Milling dry in oxygen or wet in air was dramatic with a significant reaction occurring which formed arsenolite, As2O3 and CuSO4.5H2O, both of which are readily soluble.
A small amount of SO2 was also formed. Dissolution in acid left CuS as the major phase implying incomplete oxidation. The small fraction of tennantite in the sample was comparatively resistant to oxidation.