Mineralogy and geochemistry of Rahmatabad Kaolin deposit, ghaut of Mollaahmad Nain, Isfahan Province

The Rahmatabad Kaolin deposit is located about 25 km southwest of Nain. This deposit is formed by alteration process from Eocene volcanic rocks and pyroclastic units. Mineralogical studies display that the kaolinite, jarosite, hematite, quartz, calcite, anortite, alunite, diaspore, chlorite, montmorillonite, illite, albite, orthoclase, halite, sanidine, goethite, malachite, azurite and sericite are the rock-forming minerals in this deposit. Based on geothrmometry data on the chlorite which produced by alteration process, the temperature of hydrothermal fluid formed this deposit has been between 98.25 oc to 321.04oc. According to geochemical studies, the alteration process of volcanic and pyroclastic rocks to Kaolin have been accompanied by enrichment of Rb, Cs, Ba, Sr, Nb, Hf, Zr, Y, Th, Al and U; leaching-fixation of Si, Ca, Ti, Na and P; and depletion of Fe, Mn, Mg, K Cr, Ni and RREs. Furthermore, the geochemical data can be refer to high (La/Lu)N, and high Sr, Ba values than to La, Ce and Y. Also Ce and Eu anomalies in the studied area were controlled by degree of feldspar alteration as well as changing the in degree of oxidation of environment respectively. It seems that the development of the Rahmatabad Kaolin deposit was supported by mixing of two hypogene and supergene processes. The discrepancy in the rate of alteration intensity of the source materials, chemistry of altering solutions, adsorption, incorporation in crystal lattice, difference in degree of complexation with sulfate, chloride, and fluoride ligands and difference in the stability scale of primary minerals against the alteration are considered as six important factors for controlling the mobilization, distribution, and concentration of elements in the Rahmatabad Kaolin deposit.