Hydrogeochemical and isotopic characteristics of Kayak (Seydisehir-Konya) geothermal field, Turkey

The Kayak geothermal field is located 13 km north of Seydisehir town, about 90 km southwest of Konya Province in the Central Anatolia, Turkey. This study was carried out to determine the origin, chemical characteristics, and isotopic composition of Kayak thermal waters. The measured temperatures of thermal and mineral waters range from 21.5 to 26 degrees C with a discharge of 0.8 l/s in springs, and from 30 to 45.8 degrees C with a discharge of 185 l/s in wells. Thermal and/or mineralized spring and well waters are of Ca-Na-HCO3 types with electrical conductivity ranging from 2530 to 4150 mu S/cm while cold groundwater is mainly of Ca-HCO3 and Ca-Mg-HCO3 types with electrical conductivity ranging from 446 to 668 mu S/cm. Kayak thermal waters have not reached complete chemical re-equilibrium possibly as a result of mixing with cold water during upward flow. Assessments from quartz geothermometers and fluid mineral equilibria calculations suggest that reservoir temperature of Kayak geothermal field ranges from 68 to 105 degrees C. Thermal waters are oversaturated at discharge temperatures for calcite, dolomite, and aragonite minerals corresponding to travertine precipitation in the discharge area. Gypsum and anhydrite minerals are undersaturated in all the thermal waters. The delta O-18 and delta H-2 compositions of Kayak thermal and cold waters point to a meteoric origin. Meteoric waters infiltrate the reservoir rocks along faults and fracture zones. After being heated at depth with the high geothermal gradient, they move up to the surface along faults and fractures that act as pathways. Additionally, delta O-18 and delta H-2 values suggest that thermal waters are recharged from higher elevations in comparison with cold waters. Long-term circulation of meteoric waters within the basement rocks is indicated by low tritium (<2 TU) values in the thermal waters, although the fluids do not achieve thermodynamic equilibrium. Based on the delta C-13 values, carbon in thermal waters is considered as originating from a mixture of marine carbonates and CO2 gas of volcanic (mantle) origin. (C) 2016 Elsevier Ltd. All rights reserved.