Hydrogeochemical study of the Terme and Karakurt thermal and mineralized waters from Kirşehir Area, central Turkey

The Terme and Karakurt thermal resorts are located in the center of Kirşehir city in central Anatolia. Thermal waters with temperatures of 44–60°C are used for central heating and balneologic purposes. Paleozoic rocks of the Kirşehir Massif are the oldest units in the study area. The basement of the Massif comprises Paleozoic metamorphic schist and marbles which partly contain white quartzite layers of a few tens of cm thickness. The metamorphic schists which are cut by granites of Paleocene age are overlain by horizontally bedded conglomerate, sandstone, claystone, and limestone of upper Paleocene-Eocene age. Among the thermal and cold waters collected from the areas of Terme and Karakurt, those from thermal waters are enriched with Ca–HCO₃ and cold waters are of Ca–Mg–HCO₃ type waters. The pH values of samples are 6.31–7.04 for the thermal well waters, 6.41 for thermal spring, 7.25 and 7.29 for the cold waters, and 7.52 for the Hirla lake water. EC values are 917–2,295 μS/cm for the thermal well waters, 2,078 μS/cm for thermal spring, and 471 and 820 μS/cm for the cold springs. The lowest TDS content is from water of T10 thermal well in the Terme area (740.6 mg/l). The hot and cold waters of Terme show very similar ion contents while the Karakurt hot waters at western most parts are characterized by distinct chemical compositions. There is ion exchange in thermal waters from the T5 (5), T6 (6), T12 (7), and T1 (8) wells in the Terme area. The thermal waters show low concentrations of Fe, Mn, Ni, Al, As, Pb, Zn and Cu. Waters in the study area are of meteoric origin, and rainwater percolated downwards through faults and fractures, and are heated by the geothermal gradient, later rising to the surface along permeable zones. δ¹³C_VPDB values measured on dissolved inorganic carbon in samples range from −1.65 to +5.61‰ for thermal waters and from −11.81 to −10.15‰ for cold waters. Carbon in thermal waters is derived from marine carbonates or CO₂ of metamorphic origin while carbon in cold waters originates from freshwater carbonates.