Geochemistry, fluid inclusion and stable isotope constraints (C and O) of the Sivrikaya Fe-skarn mineralization (Rize, NE Turkey)

Abstract

The Sivrikaya Fe-skarn mineralization is hosted by dolomitic limestone layers of Late Cretaceous volcano-sedimentary unit, comprised of andesite, basalt and their pyroclastites, including, sandstone, shale and dolomitic limestone layers. Intrusion of the Late Cretaceous–Eocene İkizdere Granitoid in the volcano–sedimentary unit resulted in skarn mineralization along the granitoid–dolomitic limestone contact. The ore is associated with exoskarns, and mineralization is characterized by early anhydrous garnet and pyroxene with late hydrous minerals, such as epidote, tremolite, actinolite and chlorite. The ore minerals are mainly magnetite and hematite, with minor amounts of pyrite and chalcopyrite. The composition of garnet and pyroxene in the exoskarn is Adr79.45−99.03Grs0−17.9Prs0.97−2.65 and Di69.1−77.1Hd22.2−29.8Jhn0.6−1.4, respectively, and abundances of magnetite in the ore suggest that the Fe-skarn mineralization formed under relatively oxidized conditions.Homogenization temperatures (Th) of all fluid inclusions and calculated salinity content are in the range of 166 °C–462 °C and 0.35–14.3 wt% NaCl equ., respectively. Well-defined positive correlation between Th and salinity values indicates that meteoric water was involved in the hydrothermal solutions. Eutectic temperatures (Te) between −40.8 °C and −53.6 °C correspond to the presence of CaCl2 in the early stage of fluid inclusions. On the other hand, the Te temperatures of later-stage fluid inclusions, in the range of −38 °C and −21.2 °C, correspond to the presence of MgCl2, FeCl2, KCl and NaCl type salt combinations. None of the fluid inclusions were found to contain separated gas phases in microscopy observations. However, a limited amount of dissolved CH4 was identified in the early stage, high temperature fluid inclusions using Raman spectroscopic studies.Δ18O values in both dolomitic limestone (10.8–12.5‰) and skarn calcite (7.6–9.8‰) were highly depleted compared to the typical δ18O values of marine limestones. Decreases in δ18O values are accepted as an indication of dilution by meteoric water because retrograde brecciation of garnet, magnetite and breccia filling epidote and quartz in volcanic host rocks are an indication of increasing permeability, allowing infiltration of meteoric water. Highly depleted δ13C isotopes (up to −6.5‰) of dolomitic limestone, indicate that organic matter in carbonates had an effect on the decreasing isotopic ratios. The presence of CH4 and CH2 in fluid inclusions can be explained by the thermal degradation of these organic materials.