Abstract: Gölcük (Koyulhisar-Sivas) Cu (Ag) mineralisation is hosted by Eocene basalt and andesite and pyroclastics with volcanic-volcano-sedimentary rocks. Ore minerals are bornite, chalcopyrite, covellite, chalcocite, malachite, magnetite and hematite. Alteration in the host rocks includes sericitization, argillisation, carbonation,iddingsitization and epidotization. Gangue minerals are limited to quartz and calcite. According to the analysis results for the drill core samples, 2.97% Cu and 37 g/t Ag grade was determined at an average depth of 9.7 m from the surface. Sulphur isotope values (δ34S ‰) range from -20.0 to +2.8 in surface samples and from -6.3 to +0.6 incore samples. Copper isotope values (δ65Cu ‰) range from -0.86 to +1.38 in surface samples and -1.41 to +2.69 incore samples. For Gölcük Cu (Ag) mineralization, ore mineral paragenesis, alteration mineralogy, deposit type, andisotope geochemistry values suggest that it may be a Manto-type deposit.