Bentonite deposits in Basoren Kutahya, West Anatolia, Turkey formed from alteration of perlite and pyroclastic rocks of Pliocene age. The distribution of bentonite deposits along faults in the study area indicates that the alteration solutions were hydrothermal. Although lateral zonation is observed in bentonite deposits in some regions (i.e. Demirli, Akyokus, Seklice-Sanokuz, etc.), alteration zones are extremely irregular in the Cayirlik bentonite deposit.