Original paper

Mineralogical and geochemical characteristics of the Sangab bentonite deposit, Isfehan province, Iran

Calagari, Ali Asghar; Abedini, Ali; Fatahi, Shirin

Abstract

The Sangab bentonite deposit is located ~20 km southeast of Khur and Biabanak (Isfehan province) in central Iran. This deposit is an alteration product of Eocene ignimbrites. Mineralogical studies show that the bentonites include minerals such as montmorillonite, illite-montmorillonite, beidellite, calcite, quartz, anorthite, albite, orthoclase, sanidine, microcline, and dolomite. Crystal-chemistry consideration indicates that the Sangab bentonite deposit is of Wyoming-type. Fluid inclusion studies demonstrate that the hydrothermal solutions responsible for bentonitization at Sangab had variable temperatures ranging from 140°C to less than 70°C and a narrow salinity range of 6.45-8.41 wt% NaCl equivalent. Geochemical investigations reveal that bentonitization of ignimbrites at Sangab was accompanied by depletion of Si, K, Cs, Rb, Th, V, Cu, and Ti, by enrichment of Ba, Al, Na, and Nb, and by leaching-fixation of Fe, Mg, Ca, P, Mn, Co, Hf, Sr, U, Zr, Y, Pb, Zn, and Ni. Geochemical analyses mark that variation of Eu and Ce anomalies in this deposit was controlled by the degree of feldspar alteration and oxidation potential, respectively. By considering the obtained results, it seems that factors like difference in degree of alteration intensity of the source materials, physico-chemical conditions of the environment, adsorption, incorporation in crystal structure, accessibility to complexing ligands, and difference in degree of resistance of primary minerals against alteration played prominent roles in differential mobilization, distribution, and concentration of elements in this deposit.

Keywords

iransangabignimbritebentonitealterationelemental distribution