Copper-bearing pyrite from the Coka Marin polymetallic deposit, Serbia: Mineral inclusions or true solid-solution?

We have established the presence of structurally bound copper in pyrite from the Coka Marin polymetallic deposit, Serbia, by electron-probe micro-analysis (EPMA), micro-Raman spectroscopy and X-ray powder diffraction (XRPD). Varying contents of copper in pyrite, with values LIP to 8 wt.% Cu, result in band-like textures, oscillatory and sector zoning. We observed a correlation between increasing copper content and decreasing wavenumbers of Raman band positions and increasing band-widths. Moreover, the lattice parameter of 5.422 angstrom for Cu-beariing pyrite is greater than that for pure pyrite. Besides pyrite with structurally bound copper, a texturally different type of pyrite was observed in the same sample. The latter also contains copper, but only in the form of admixed copper-bearing minerals. We propose that pyrite with structurally bound Cu was formed by the recrystallization of colloform pyrite enriched in copper.