Geochemistry, microthermometry, and C and O isotope constraints on the origin of the Düzköy Fe-Cu skarn deposit (Gümüşhane, NE Turkey)

Abstract

The Fe-Cu-type Düzköy skarn deposit occurs along the contact between the Lower Cretaceous Berdiga limestone and the Eocene-aged Harşit granitoid. The endoskarn zone is characterized by the presence of granular pyroxenes, while garnet, epidote, quartz, and calcite are commonly defined in the exoskarn. Fe-Cu-type skarns were identified according to the mineralogical properties, garnet (Ad0-8.81Gr59.69-78.65Py21.35-38.11) and pyroxene (Hd0.29-38.64Di61.09-99.02Jo0.06-1.26) compositions, and Mn/Fe ratios (in the range of < 0.1 to 3.75) of pyroxenes. The geochemistry of the Harşit granitoid is also compatible with Fe-Cu-type skarns according to the high MgO (2.41 wt%) and low K2O (2.05 wt%), as well as Rb-Sc and Rb/Sr-Zr contents. Therefore, the coexistence of both oxide and sulfide phases was found to be closely associated with the geochemical features of the Harşit granitoid. Higher homogenization temperatures (Th, up to 483 °C) and salinity (up to 44.4 wt% NaCl equ.) of the early-stage fluids correspond to magmatic-dominated fluids. In contrast, the decreasing Th and salinity as low as 168 °C and 1.1 wt% NaCl equ., respectively, refer to a mixture of meteoric water through the later stages. The ?13C isotopes of skarn calcites (between ? 1.62 and 2.77‰) are compatible with marine carbonates, while their ?18O rates, ranging from 9.04 and 24.5‰, are highly depleted. Further depletion of ?18O isotopes (down to 3.47‰), calculated from the equilibrated fluids with calcites, while ?13C isotopes were stable, is indicative of the mixing of magmatic and meteoric waters, and these results comply well with the fluid inclusion data. © 2020, Saudi Society for Geosciences.