Hydrochemical and isotopic properties of the Mahmutlu and Bagdatoglu mineralized thermal springs, Kirşehir, Turkey

The present study identifies the hydrochemical and isotopic properties of the Mahmutlu and Bagdatoglu mineralized thermal springs in Kirşehir province, a geothermal field in central Anatolia, Turkey. Based on these properties, a hydrogeological regime is proposed in order to explain the Mahmutlu-Bagdatoglu geothermal system. The relation between the concentrations of the environmental stable isotopes deuterium and oxygen-18 in the water is similar to the relationship in global meteoric water, indicating that the water is of meteoric origin. Evaluation of the geochemical characteristics of the water reveals that these two thermal springs belong to the same hydrogeological system. The hydrogeological system comprises a fractured limestone member of the Çevirme Formation and the Kervansaray Formation as reservoir rocks, and the Deliceirmak Formation as an overlying aquitard. The waters of the Mahmutlu and Bagdatoglu springs are mainly of the Na-Cl-SO4 type that originate from the Pohrenk evaporite. The thermal waters are undersaturated with respect to calcite, dolomite, halite, and gypsum. The ?18O and ?2H contents indicate a ?18O shift in the Mahmutlu and Bagdatoglu waters. The temperature range of the two reservoirs is estimated to be 98-158°C, on the basis of Na+K+Ca and SiO2 geothermometers. © Springer-Verlag