Element mobility during the formation of the Uzunisa-Ordu Bentonite, NE Turkey, and potential applications

Dacitic andesitic calc-alkaline lavas and their pyroclastic rocks of Upper Cretaceous age are widespread in the Ordu area, eastern Black Sea Coast of Turkey. Ca-bentonite and Ca/Na-bentonite deposits with significant economic potential formed in the broader region. The mineralogy and geochemistry of these deposits were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analyses. The parent rocks (PR) and bentonite samples were analysed for the major and trace element contents, including rare-earth elements, to understand the effect of differential alterations on element mobility. The bentonites contain mainly di-octahedral Ca-montmorillonite with minor amounts of illite, quartz, calcite, dolomite and feldspar. Primary K-feldspar and plagioclase phenocrysts were altered in the bentonite horizons, and were completely leached at greater depth. For this reason, the higher quality bentonites are found at deeper zones. Bentonite horizons are characterized by relatively high loss on ignition (LOI: 9.8-20.8%) and MgO content (3-5%) and low K2O (