The technique of fluorescence REFLEXAFS was used to examine the activation by copper of sphalerite, ZnS, and the subsequent interaction with a xanthate collector at pH 10 and 12. ZnSe was used as an isostructural analogue of ZnS to avoid the contribution from the xanthate S on the mineral surface being swamped by that from the substrate S. On activation, the copper interaction with the Se or S atoms is clearly seen and Cu-O bonds are formed. On the addition of xanthate, the oxygen is displaced by sulfur and a covellite-like species develops at the surface. The iron at the surface in natural sphalerites is bonded to oxygen, inhibiting initial copper activation but appears to catalyse covellite formation on xanthate addition. The technique succeeds in producing direct structural information, providing information complementary to other investigative techniques.