Platinum-Group Element, Stable Isotope, and Fluid Inclusion Investigation of the Ultramafic Rock-Hosted Gunes-Sogucak Ni-Cu-Sulfide Mineralization in the Gunes Ophiolite, East-Central Turkey

Abstract

Gunes-Sogucak Ni-Cu-sulfide mineralization in the Divrigi district of Sivas Province is genetically related to Late Cretaceous ultramafic rocks. Disseminated mineralization is scattered through the ultramafic rocks, whereas vein-type mineralization is present in fracture zones in them. Both disseminated and vein-type Ni-Cu-sulfide mineralization show enrichment of platinum-group elements (PGE), Au, and Ag relative to primitive mantle. Average metal concentrations of the Cu-Ni-sulfide mineralization are: Ni: 106, Cu: 263 ppm; Ru: 293, Pt: 26, Pd: 126, Au: 87, Ag: 316 ppb. Enrichments in PGE, Au, and Ag may have resulted from the chemical evolution of hydrothermal fluids. δ34SΣS values range from 7.9 to 14.6‰, with most values at the higher end. Judging by the range of sulfur isotope values, a component of sedimentary sulfate evidently was present in the hydrothermal fluids. δD values of waters trapped in quartz crystals range from -69 to -90‰, and δ18O values of quartz range from 11 to 15‰. Based on δ18O and δD data, combined with the geologic setting of the deposits, we propose that the ore fluids were dominated by magmatic waters. Sulfur isotopes indicate that ultramafic rocks assimilated a portion of their sulfur from sedimentary sulfates during ascent through the crust. Fluid inclusion data indicate that hydrothermal mineralization with PGE enrichment formed at a minimum temperature of around 280-300°C during percolation of high-salinity fluids through the ultramafic rocks.