Mineralogy and geochemistry of Upper Cretaceous Mazıdağı Phosphorite Deposits from the Northern Arabian Plate (Mardin, Turkey)

In the Mardin-Mazıdağı region, which corresponds to the northern Arabian Plate, layers containing marine phosphorite rocks are found within the Karababa Formation (Upper Cretaceous). The Karataş member contains phosphorites and carbonate rocks with nodular chert geodes and fossils. The phosphorite and micritic limestones contain invertebrate fossil fragments and materials such as optical isotropic pelletic apatite minerals, angular/subangular and plated fish bone fragments, and brachiopod shells. SEM (scanning electron microscopy) results show that the apatite minerals are either spherical or ellipsoidal in shape and their size varies between 100–200 μm. According to X-ray diffraction (XRD) examinations, the rocks contain apatite (carbonate rich fluorapatite; CFA), carbonate (calcite, dolomite), silica (quartz and opal-CT), little feldspar, and clay (smectite, palygorskite/ sepiolite, kaolinite, illite, chlorite, mixed layered chlorite-vermiculite (C-V) and illite-vermiculite (I-V). The average major and trace elements found in the phosphorite include P2O5 (35.41 wt.%), REE s (44.57 ppm), Y (52.85 ppm), and U (5.45 ppm). The Mazıdağı phosphorite analysis indicates that the conditions are slightly oxic, which is supported by their slightly negative Ce anom average values (–0.30), low Ce/La ratios (0.32), and a V/(V + Ni) mean of 0.93 ppm. All the recoded values of the average REE for the study area are considerably lower than those in Iraq (84.30 ppm), Tunisia (400.3 ppm), Morocco (571.75 ppm) and Jordan (187 ppm). It is inferred that mineral formation processes are affected by the biogenic and biogeochemical activities that occurred in conjunction with the changes in sea level driven by the tectonic conditions associated with the evolution of the Neotethys Ocean.