Mineralogy and Geochemistry of Ortaklar Volcanic-Hosted Massive Sulfide deposit within Kocali Complex in Gaziantep, Turkey

Abstract

The study area called the Ortaklar mineralization is located in the Gaziantep province, Turkey. The area is also included in the Southeast Anatolian orogenic belt, between Tauride (in the north) and Arabian platform (in the south), which was developed as a result of closure of Neotethyan ocean during upper Cretaceous-Miocene periods reported by numerous authors. In particular, massive sulfide mineralization is hosted in basalt and pillow lavas which is one unit of the Kocali Complex including other two units mainly characterized by sedimentary rocks (chert, radiolarite and limestone), and serpentinite. The orebody is underlain and contacted with radiolarian chert and generally parallel to the thrust lines (E-W/30-60 North). For this study, samples mainly have been collected from open pit but also include some core samples. For mineralogical study, it was examined with unaided eyes and under as well as microscope electron probe. Under microscope pyrite, magnetite and chalcopyrite are abundant with minor minerals such as bornite, covellite, chalcocite, sphalerite, siderite, hematite and goethite. The basalt are mainly composed of plagioclase, k-feldspar, clinopyroxene and a small amount of calcite and quartz. The composition of plagioclase ranging from An77.33 to An88.35 with an exceptional plagioclase of Ab99.57 was identified using electron probe. Almost clinopyroxenes in basalts have a very limited compositional range of Mg#80.85-87.91, but few sodic-calcic pyroxenes were also analyzed. Chert as pelagic sediment has spherical radiolaria skeletons and their long thin spines. Serpentinite in the study area has relict crystals of olivine within the network of serpentine in parts of serpentinite. It has mesh texture and some brown stains of iron oxides and Cr-spinel. Six samples of massive ores and seven samples of related rocks have been analyzed in terms of major, trace and rare earth element (REE) concentrations using X-ray fluorescence (XRF) spectrometer and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). To classify the Ortaklar deposit among many VMS types, the base metal contents of the ores and host rocks from the study area were plotted in a ternary diagram indicating Cyprus type VMS deposit. Relatively immobile elements such as Ti, Zr, Y, Nb, Th and REEs in basalts were used for various diagrams to obtain the information of origin of magma and tectonic environments. Sulfur stable isotope study was also conducted. The pyrite and chalcopyrite separates from ore specimens show a narrow range in δ34S values of 2.7 to 5.7 per mil with average δ34S value of 4.4, except for two low values of -7.8 and -17.6 per mil. The bulk sulfur isotopic composition from three basalt was analyzed. The results could be interpreted as various affects such as sea water, basalt (host rock) as well as bacterial reduction sulfides.