Acta Geodynamica et Geomaterialia

Title: MINERALOGY, GEOCHEMISTRY AND GENESIS OF MOLLAAHMAD PASS BENTONITE DEPOSIT, NAEIN, ISFAHAN PROVINCE, IRAN
Authors: Fatahi Shirin, Mackizadeh Mohamadali, Khani Nader and Bayat Sima
DOI: 10.13168/AGG.2020.0005
Journal: Acta Geodynamica et Geomaterialia, Vol. 17, No. 1 (197), Prague 2020
Full Text: PDF file (16.2 MB)
Keywords: Bentonite, geochemistry, Rare earth elements, Lacustrine, Mollaahmad Pass, Iran.
Abstract: The Mollaahmad pass bentonite deposit occurs within an area of about 10 km2 with Oligo-Miocene age (Isfahan- Iran). This bentonite deposit with two general lenticular and layered forms has extended in the tuff, conglomerates and sandstones (including volcanic fragments). XRD studies are demonstrating that montmorillonite, montmorillonite-illite, nontronite, albite, anorthite and quartz are major and clinoptilolite, heulandite, sanidine, orthoclase, calcite, microcline and actinolite are minor constituent minerals in studied bentonite deposit. Moreover, mineral chemistry indicates that Mollaahmad pass bentonite deposit has intermediate to di-octahedral smectites, so it can be classified as Wyoming bentonite type. Based on geochemical studies, transform process of parent rocks into bentonite was accompanied by enrichment of Cr, Sb, Se and REEs, and also enrichment or depletion of other major and trace elements. More geochemical studies have shown positive to negative Eu and Ce anomalies. This can be related to change in rate of oxidation and alteration intensity in altered system. In addition, study of rare earth elements indicates high differentiation of LREEs from HREEs that related to egress of HREEs from environment in form of carbonate complexes. It seems that six factors including discrepancy in rate of alteration intensity of the source materials, incorporation in crystal lattice, complex-forming ligands, surface adsorption and difference in stability of primary minerals are able to control mobilization, differentiation and distribution of elements in studied bentonites. This bentonite deposits has formed in margin of lacustrine environment.