The behavior of elements in the process of alteration of andesite - basalt to bentonite in Tashtab Mountain, Khur, northeastern Isfahan province

Tashtab Mountain is located 25 km from the city of Khur in northeastern Isfahan province. Several bentonite mines formed in this area as a result of the Eocene volcanic alteration. These mines are classified as the Khur bentonite horizon. Studies on trace elements in parent rock and clays show that the studied bentonites formed from andesite-basaltic parent rocks. The XRD analysis shows that studied clay minerals consist of Na-montmorillonite with a low amount of kaolinite. In addition, there are quartz, calcite and crystobalite. The alteration process leached most of major and trace elements. Most of removing in major elements happens in alkaline elements, and in trace elements LILEs show most of depletions. Al and Ti are immobile elements and show lower amount of changes. Cu is the metal that shows most depletion among other metal elements in contrast Ni, Cr and Zn shows a little enrichment also, the trend of REEs is similar to parent rock with a difference. HREEs are more depleted than LREEs. It may happen because of leaching of HREEs as complexes and absorbing of LREES into the clay minerals structure.