Hydrochemical and isotopic properties of Heybeli geothermal area (Afyon, Turkey)

The thermal waters at the Heybeli (Kızılkirse) low-temperature geothermal field located in the Afyonkarahisar Province (western Turkey) are discharged from Paleozoic recrystallized limestone. The temperature, specific electrical conductivity, and pH values of the thermal waters are within the range of 28.9 to 54.7 °C, 587 to 3580 μS/cm, and 6.32 to 7.37, respectively. The Heybeli geothermal system is fed by meteoric waters. The waters are heated at depth by high geothermal gradient caused by the neotectonic activity in the deep and ascend to the surface through fractures and faults by convection. The thermal waters are of Na-Ca-HCO 3 -SO 4 type and their chemical composition of the waters is mainly controlled by water-rock interaction and mixing processes. The δ 18 O, δ 2 H and tritium compositions show that the thermal waters are of meteoric origin and the residence time at the reservoir is longer than 50 years. Isotope data (δ 34 S and δ 13 C) indicate recrystallized limestones as origin of CO 2 and structural substitution of sulfate into marine carbonates (CAS) as origin of sulfur. Chemical, δ 18 O ( SO 4 - H 2 O ) isotope geothermometers and mineral equilibrium diagrams applied to thermal waters gave reservoir temperatures between 62 and 115 °C. Saturation index calculations show that the most expected minerals causing scaling at outflow conditions during the production and utilization of Heybeli geothermal waters are calcite, aragonite, dolomite, quartz, and chalcedony.