Mineralogical and geochemical studies to determine genesis of Khalkuh bentonite mine, Ferdows, Southern Khorasan

The Khalkoh bentonite mine is located in Ferdows، southern Khorasan province. In this research، genesis of Khalkoh mine was determined using mineralogical and geochemical studies. Analytical methods including x-ray diffraction (XRD) and chemical analyses (XRF and ICP-MS) performed on bentonite and country rock samples as well. The studied bentonites consist mainly of sodium montmorillonite. They also contain cristobalite، quartz، albite، calcite، halite and illite as minor phases. The stratabound nature of minerals، high amount of montmorillonite، the presence of gypsum layers alternating with bentonite and the lack of hydrothermal alteration indicate that bentonite deposit was formed in the diagenetic process by means of volcanic glasses alteration to bentonite in the lagoon. In spite of leaching of alkalies، the Si has not been leached from the system. This is supported by the presence of opal-CT and quartz and generally، shows the low fluid flow rate in the system. Based on the geochemical data، the parent magma and rock series are rhyodacite/dacite and calc-alkali series، respectively، formed in volcanic arc setting.