Eshkaftouk bentonite: constraints on geology, physical, mineralogical and geochemical characteristics (northwest of Birjand)

Eshkaftouk bentonite mine is located in the northwest of Birjand and eastern part of Lut block. This bentonite is the product of alteration of Tertiary andesitic lavas and associated tuffs. Geochemical characteristics show that bentonite parent rocks have andesitic composition and bentonite samples have andesite to dacite-rhyodacite composition.The magmatic series of all samples is calc-alkaline type. Mineralogical analysis (XRD) shows that the main minerals forming of bentonites include montmorionite, anorthite, cristobalite, and quartz with small amounts of illite, muscovite, kaolinite, microcline and dolomite. Electron microscope images of bentonite samples show that smectite (montmorionite) is the most abundant mineral in these samples that are characterized by flaky morphology with rugged edges, honeycomb and cornflake. The results of energy dispersive spectroscopy (EDS) studies also indicate that the predominant mineral forming  of bentonites is sodium-calcium montmorionite, and accordingly, Eshkaftouk bentonite is Wyoming-type. Investigation of mass changes of major and trace elements of Eshkaftouk bentonite indicating loss of K2O, Na2O, CaO, MgO,MnO and LILE such as Ba, Rb, Sr and gains of SiO2, Al2O3 and Fe2O3.