Abstract: The majority of the pyroclastic flow deposits in the Central Anatolia Volcanic Province (CAVP) havealready been subjected to hydrothermal alteration. In this study, we aimed to identify the dominant alteration typeunder different conditions and reveal the physicochemical conditions and geological processes that influencedsecondary mineral formation. The Zelve ignimbrite represents one of the most hydrothermally altered pyroclasticflow units in the study area. Juvenile pumice fragments from the Zelve ignimbrite were reacted with alkaline solutionsunder controlled experimental conditions, and reaction products in the form of zeolites were identified. Experimentalstudies were carried out under autogenic pressure and using alkaline solution activity agents such as NaOH, KOH,and NaHCO3 at a temperature of 150 °C, considering the most effective hydrothermal conditions in the region. Thereaction products obtained in experimental studies were identified by X-ray diffraction (XRD) and characterized  by scanning electron microscopy (SEM). As a result, zeolite minerals such as phillipsite (K- and Na-), analcime,mordenite, and chabazite were synthesized. We concluded that NaOH alkaline solution is an effective activity agentin the formation of zeolite minerals during hydrothermal alteration of a juvenile volcanic product. In addition,zeolite phases naturally crystallizing in the region (analcime, phillipsite, chabazite, mordenite, clinoptilolite, anderionite) mostly coincide with the reaction products from experimental studies. Major and trace element compositionsof reaction products exhibited distinct differences with respect to starting composition. Reaction products wereenriched in major oxides of Na2O, K2O and CaO, whereas they were depleted in trace element concentrations of Rb,Ba and P. This indicates elemental exchange occurred between the solution and starting material to form zeolites.