Major and minor element geochemistry of chromite from the Xerolivado-Skoumtsa mine, Southern Vourinos : Implications for chrome ore exploration

The concentration of major (Cr, Al, Mg, Fe) and minor (Ti, V, Mn, Ni, Zn) elements was studied in chromitite ores and accessory chrome spinels within serpentinite host rocks from the Xerolivado-Skoumtsa mine (Southern Vourinos, Western Macedonia, Greece) by means of electron microprobe techniques. Chrome ores in the mine occur in seven extensive ore bodies. Chromite was analyzed with respect to its position within or between ore bodies, including the following classifications: chromitite (schlieren ore) band, accessory chromite in intercalated serpentine within the ore bodies, disseminated chromite in non-ore bearing host rocks, and chromite within serpentinites intermediately adjacent to ore bodies. Chrome spinel originally forms at temperatures of around 1300 °C, but their hosts undergo ductile deformation to temperatures down to around 700 °C, thus facilitating solid state re-equilibration. Results showed that Mg in chromite was found to be substituted during re-equilibration mainly by Fe and, to a minor extent, by Mn and Zn. Cr is mainly substituted by Al and, to a minor extent, V. Compositions were found to vary in accessory chromite crystals as a function of their distance from chromitite bands. Specifically, the average concentrations of Cr and Mg are higher in spinels within chromitite ores than for the disseminated spinels in serpentine gangue layers within chromitites. Chrome spinels in schlieren ore layers have higher Mg and Cr concentrations compared to the disseminated chromites in the serpentinites immediately adjacent to the chromite ore bodies and also slightly higher concentrations of Mg and Cr than the disseminated chromites in the host serpentinites. Fe2+, Mn, Zn, Al and V cations show exactly the opposite trend. We attribute these variations in the spinel chemistry to subsolidus reactions between chromite, silicate mineral phases and fluids. Geochemical maps presenting the spatial variation of these elements in disseminated Cr spinels of the Xerolivado mine can serve to delineate the precise position of the chrome ore bodies.