Hydrogeology and hydrogeochemistry of a coastal low-temperature geothermal field: a case study from the Datça Peninsula (SW Turkey)

Abstract

The thermal springs at the Gölbaşı geothermal field located in the southwest coastal region of Turkey discharge from the Mesozoic-aged fissured carbonate aquifer. The temperature, specific electrical conductivity and pH values of the thermal waters are, respectively, 21.6–29.4 °C, 4020–57,200 µS/cm and 6.85–7.35. Thermal waters are Na–Cl-type brackish to saline waters. The Gölbaşı geothermal system is fed by meteoric waters and local seawater. The waters are heated at depth by high geothermal gradient caused by the recent tectonic activity in the deep and ascend to the surface through fractures and faults by convection and emerge as thermal springs. The thermal waters mix in different proportions with seawater (5–58 %) and fresh cold waters during the moving up to the surface. Isotope data (?18O, ?2H and tritium) show that the thermal waters are of meteoric origin, and the residence time at the reservoir is at least 50 years. Almost all the waters are saturated with respect to Ca-montmorillonite, gibbsite, K-mica, illite, kaolinite, Fe (OH)3(a), calcite, dolomite and barite minerals. The most expected minerals that cause scaling at outlet conditions during the production and utilization of Gölbaşı geothermal waters are calcite, dolomite and some barite. Various chemical geothermometers, Na–K–Mg ternary diagram and mineral equilibrium diagrams suggest that the reservoir temperature is around 50–100 °C. © 2016, Springer-Verlag Berlin Heidelberg.