The Chah-Shur clay deposit is located in 150 km southeast of Isfahan. Eocene igneous rocks and Quaternary deposits cover the area. Eocene volcanic rocks include andesite and tuff. The rocks belong to magmatic activities of Urumieh-Dokhtar magmatic belt. Alteration of the vitric and lithic tuff units has produced the clay deposit. Based on the petrographic studies the main minerals in tuff units are plagioclase, K-feldspar and quartz. The major phases in clay deposit are kaolinite, illite, montmorillonite, quartz, albite and orthoclase. Also, muscovite, chlorite and hematite are as minor phases. The mineralogical studies show an intermediate alteration. The clay deposits can be formed by supergene or hypogene processes; while the combination of both of them can result in the formation of mixed type clay. The geochemical data of Chah-Shur clay deposit show scattering between hypogene and supergene types. The abundance of Fe2O3+TiO2 vs Cr+Nb and Zr vs TiO2, as well asSr+Ba vs Ce+Y+La suggest mixed and hypogene types. On the other hand, P2O5 and SO3 plot shows the supergene and mixed types. The results obtained from mineralogical and geochemical studies indicate that the genesis of the Chah-Shur clay deposit can be considered mixed type.