Crystallography and Surface Oxidation of Stoichiometric Arsenopyrite from Sumadija-Kopaonik Pb-Zn/Polymetallic Ore District (Serbia)

The behaviour and stability of arsenopyrite largely depend on its crystal structure, but studies of crystallography and structural defects are scarce. For clarification, we investigated a series of natural arsenopyrite crystals from the polymetallic Pb-Zn-(+/- Cu,Ag,Au,Sb,Bi,W) Sumadija-Kopaonik ore district (Serbia) by powder X-ray diffraction (XRPD). Among them, samples from the Drenjak gold mineralisation showed near-stoichiometric FeAsS composition and were further investigated by conventional and high-resolution transmission electron microscopy methods. TEM revealed abundant planar crystallographic defects and epitaxial surface oxide layer formation upon air exposure. Our findings present the fundamental work on the prototype arsenopyrite structure and have further implications for studies on ion incorporation into FeAsS structure and its environmental stability and oxidation mechanisms as a source of anthropogenic As release into the environment.