Hydrogeochemistry of the thermal waters from the Yenice Geothermal Field (Denizli Basin, Southwestern Anatolia, Turkey)

The chemical and isotopic properties of thermal waters (Kamara and Cizmeli) and cold springs from the Venice Geothermal Field (YGF), in southwestern Anatolia, Turkey are investigated in order to establish a conceptual hydrogeochemical-hydrogeological model. These thermal waters derive from Menderes metamorphic rocks and emerge along normal faults; they are commonly used for heating of greenhouses and bathing facilities. Discharge temperatures of thermal waters are 32 degrees C to 57 degrees C (mean 51 degrees C) for Kamara and 35 degrees C to 68 degrees C (mean 47 degrees C) for Cizmeli, whereas deep groundwaters are 15 degrees C to 20.1 degrees C (mean 17 degrees C) and shallow groundwaters ware 12 to 16 degrees C (mean 15 degrees C). Kamara and Cizmeli thermal waters are mostly of Na-Ca-HCO3-SO4 type, whereas deep groundwaters are Ca-Mg-HCO3 and Mg-Ca-HCO3 types and shallow groundwaters are mainly Mg-CaSO4-HCO3 and Ca-Mg-HCO3 types. In the reservoir of the geothermal system, dissolution of host rock and ion-exchange reactions changes thermal water types. High correlation in some ionic ratios (e.g. Na vs. Cl, K vs. Cl, HCO3 vs. Cl) and high concentrations of some minor elements (e.g., As, Sr, B, Cl, F) in thermal waters likely derive from enhanced water-rock interaction. Water samples from YGF have not reached complete chemical re-equilibrium, possibly as a result mixing with groundwater during upward flow. Geothermal reservoir temperatures are calculated as 89-102 degrees C for Kamara and 87-102 degrees C for Cizmeli fields, based on the retrograde and prograde solubilities of anhydrite and chalcedony. Based on the isotope and chemical data, a conceptual hydrogeochemical-hydrogeological model of the YGF has been constructed. Very negative delta O-18 and delta H-2 isotopic ratios (Kamara: mean of 8.43 parts per thousand and 56.9 parts per thousand, respectively and Cizmeli: mean of -7.96 parts per thousand and - 53.7 parts per thousand, respectively) and low tritium values (<1 TU) reflect a deep circulation pathway and a meteoric origin. Subsequent heating by conduction in the high geothermal gradient setting (resulting from regional crustal thinning) drives geothermal waters upwards along faults and fractures that act as hydrothermal pathways. Positive delta C-13 ratios (+9.45 parts per thousand for Kamara and +7.28 parts per thousand for cizmeli) indicate a metamorphic origin of thermal waters. Negative carbon isotope ratios (-8.40 parts per thousand) found in the cold groundwaters are linked to exchange in freshwater carbonates of the Sazak Formation. (C) 2015 Elsevier B.V. All rights reserved.