Mineralogy, geochemistry and genesis of clays in the Tekneli and Delikkaya (Turkey) carbonate-hosted sulphide and non-sulphide Pb-Zn deposits

The Tekneli and Delikkaya carbonate-hosted sulphide and non-sulphide Pb-Zn deposits formed along faults and karstic cavities under the control of hydrothermal fluids with subsequent supergene oxidation in limestones and dolomitic limestones. Sulphide (galena, sphalerite, pyrite) and non-sulphide minerals (smithsonite, cerrusite, goethite, and hematite) were found to be present. XRD patterns and Fourier Transform Infrared (FTIR) spectroscopic analyses show that fraipontite is predominant among Zn clay minerals, with lesser amounts of sauconite (Zn smectite), and illite. SEM images of smectite, illite, chlorite from karst-filled “red clays” coating and filling pores suggest their detrital origin. Zn clays (fraipontite and sauconite) developed in situ on detrital illite and mixtures of detrital red clays. SEM-EDX analyses show that the fraipontite contains a higher content of Zn (14.8%) compared to sauconite (10.2%). The plots of Al2O3 vs. SiO2, TiO2 vs. Al2O3, light rare earth element (LREE) enrichment, nearly flat heavy rare earth element (HREE) patterns, and Eu and Ce anomalies in the clays, suggest sediments dominated by felsic and some mafic rock sources and derived from seawater or porewater under oxidizing conditions. The enrichment relative to upper crustal compositions (UCC) indicates alteration of feldspar under warm and humid climate conditions during weathering. The red clay type residual clays originated from ophiolitic, carbonate, mudstone, siltstone, and marl host rocks and were transported to karst cavities as breccia matrices by groundwater after limestone dissolution in the study area. Zn clays related to red residual clays in the karstic cavities formed either by direct precipitation of meteoric fluids or grew over detrital illite.