Re-Os Age and Stable Isotope (O-H-S-Cu) Geochemistry of North Eastern Turkey’s Kuroko-Type Volcanogenic Massive Sulfide Deposits: An Example from Cerattepe-Artvin

Abstract

The eastern Pontide tectonic belt (EPTB) contains greater than 350 identified Kuroko type volcanogenic massive sulfide deposits/mineralization/occurrences (VMSD). The deposits are associated with Late Cretaceous felsic volcanics consisting mainly of dacitic and rhyolitic lavas and pyroclastics that outcrop within a narrow zone running parallel to the eastern Black Sea coast and represent the axial zone of a paleo-magmatic arc. The Cerattepe deposit is the second-largest and is a hybrid VMS system with some epithermal features. To date, no geochemical research constrains the origin and timing of mineralization in the Cerattepe VMS deposit. Here, we provide Cu, O, H and S, isotope analysis of ores and alteration minerals to understand the hydrothermal history of the deposit and date the massive ore with Re-Os geochronology. Secondary weathering mobilized and redistributed metals in the deposit. The copper isotope signatures of shallow ores in the gossan follow patterns resulting from oxidative weathering of copper minerals with gossan Fe oxides of δ65Cu = −2.59‰, enrichment zone copper sulfide of d65Cu = +2.23 and +1.73‰, and primary ores of δ65Cu = +0.71 and +0.41‰. At the boundary of the enrichment zone, further cycling and migration of enrichment zone copper are evidenced by two samples having larger ranges of the δ65Cu = +3.59‰, and −2.93‰. Evidence for a magmatic source for fluids and S are evidenced by the O and H isotope values from quartz veins (δ18O = +7.93‰ to +10.82‰, and δD = −78‰ and −68‰) and sulfides that possess δ34S ratios of –5 and 0‰ from drill core samples. 187Os/188Os–187Re/188Os ratios from drill core sulfide samples of Cerattepe VMS deposit yields a 62±3 Ma isochron age and a highly radiogenic Os initial ratio. This age is compatible with silicate alteration ages from a proximal deposit and clearly shows mineralization occurs at a much younger time than previously proposed for VMS mineralization in the eastern Pontides. The new Re-Os age and source of Os imply that mineralization in the area occurs at a distinctly younger interval in the back-arc basin and metals could be sourced from the surrounding host rocks.