Mineralogy and geochemistry of gossans developed on selected Kuroko–type VMS deposits occuring in eastern pontides (NE Turkey)

Eastern Pontides form a mountain chain through northeastern Turkey which is 500 km in length and 100 km in width. East-west-trending tectonic zones of Eastern Pontides are Beldağ basin fill, the ophiolite belt, Yıldızeli Basin fill, and the magmatic belt. Permian granitoids and Devonian-Carboniferous metamorphic rocks are the oldest rocks in the region forming the basement rocks. Eastern Pontides implicate a highly complex volcanic arc system which is one of the four major tectonic units of Turkey. The magmatic arc developed over the northward-subducting Neotethyan oceanic plate. Volcanic sequences may reach up to 3 km in thickness and it subsists of a upper portion of the section led by felsic flows pyroclastic deposits and breccias while the lower portion led by mafic and intermediate lavas. Late Cretaceous section felsics volcanic rocks which are upper part are associated with the VMS. Volcanogenic massive sulphide (VMS) deposits, also known as volcanic-associated, volcanic-hosted, and volcanosedimentary - hosted massive sulphide deposits, are major sources of Zn, Cu, Pb, Ag, and Au, and significant sources for Co, Sn, Se, Mn, Cd, In, Bi, Te, Ga, and Ge. They typically occur as lenses of polymetallic massive sulphide that form at or near the seafloor in submarine volcanic environments, and are classified according to base metal content, gold content, or host-rock lithology. There are over sixty VMS occurrences in the Eastern Pontides. Studied samples were taken from İsrail, Cerattepe, Killik, Karaerik, and Kızılkaya deposits. Gossan is the weathered portion of an ore deposit which contains plenty of oxides and hydroxides. Gossan is formed by the dissolving of sulfides due to high oxidation potential of the environment. For mineralogical and geochemical characterization of gossan samples, XRD, XRF, Ore Microscopy, and EPMA have been used. Major minerals that have high and consistent presence include iron oxides, quartz, sulfates and some clay minerals. Minor to trace sulfides (e.g., pyrite) and native elements (e.g., gold and silver) were also observed. According to XRF results the highest Au was observed with 1.105 ppm in Cerattepe however highest Ag was observed in İsrail with 16.3 ppm.