Eocene magmatism and associated Fe-Cu mineralization in northeastern Turkey: a case study of the Karadag skarn

Abstract

The metallogenic belt containing numerous skarn mineralized systems starting from Eastern Europe continues through Turkey and Iran. The study area in the Eastern Pontides is within this metallogenic belt. The 44.39 +/- 0.53 Ma Karadag Intrusion sourced skarn mineralization is located along the granitoid-to-limestone contact. The Karadag Intrusion is an arc-like pluton with medium-high K calc-alkaline and peraluminous-metaluminous affinity. The Karadag Fe-Cu skarn mineralization (Gumushane, Turkey), an exoskarn, is hosted by Late Cretaceous limestone and consists of early garnet, clinopyroxene, and orthoclase with late epidote and chlorite. Primary ore minerals are magnetite and haematite, accompanied by minor amounts of chalcopyrite and pyrite. Pyroxene comprises mostly diopside and less hedenbergitic diopside and johannsenite. Wollastonite is very rare. Garnet is andradite and grossular-andradite. Thus, all these results imply that the Karadag Fe-Cu skarn mineralization formed under relatively oxidized and Fe-rich conditions. The homogenization temperatures of the fluid inclusions vary from 189 degrees C to 405 degrees C for quartz and 186 degrees C to 430 degrees C for calcite. The salinity contents in the fluid inclusions are within 0.2-9 wt% NaCl equivalent for quartz and 0.4-14.8 wt% NaCl equivalent for calcite. First melting temperatures between -36.5 and -47.4 degrees C were attained with the presence of NaCl-FeCl2 +/- CaCl2 in the initial phase of fluid inclusions. The first melting in the later stage of fluid inclusions is between -3.8 and -17.2 degrees C, thereby, supporting the existence of NaHCO3-Na2CO3-KCl-type salt composition. The delta O-18 values of minerals are 1.7-10.3 parts per thousand for garnet, 11.1-14.6 parts per thousand for quartz, 6.4 to 6.8 parts per thousand for epidote, and 2.8-3.8 parts per thousand for magnetite in the Karadag skarn mineralization. The delta O-18 value of epidote indicates magmatic fluid, whereas those of garnet, magnetite, and quartz suggest magmatic fluids together with less meteoric effect. The delta O-18 values in limestone (18.7 to 22.3 parts per thousand), marble (8.7 parts per thousand), and calcite (10.5 to 12.2 parts per thousand) were depleted relative to typical delta O-18 contents of marine carbonates (20 to 30 parts per thousand). Moreover, the C isotope values of calcite (-5.4 to -1.4 parts per thousand), marble (-2.1 parts per thousand), and limestone (1.0 to 1.2 parts per thousand) reflect those of metamorphic rocks and skarns (-4.0 to 3 parts per thousand and -18 to 2 parts per thousand). Mineral paragenesis, fluid inclusion, and stable isotopic signatures are consistent with ore mineralization caused by the interaction of magmatic fluids with carbonate host rocks. Karadag Fe-Cu skarn mineralization, associated with Karadag postcollisional magmatism, is an example of skarn mineralized system in the Eastern Pontides.