Geological and Hydrogeochemical Properties of Heybeli (Afyonkarahisar) Geothermal Field, Western Turkey

Abstract

The Heybeli (Kizilkirse) geothermal field located at 25 km south-east of Afyonkarahisar province (western Turkey) is one of the important geothermal sites in the region. The basement rocks in the study area are the Paleozoic metamorphics and recrystallized limestones. This Paleozoic basement is overlain by Senozoic marl-conglomerate-sandstone-mudstone, tuffite, trachyandesite and alluvium units. The Paleozoic recrystallized limestone is the reservoir rock for the thermal waters whereas the Senozoic impermeable units are the caprock. The Heybeli geothermal area is controlled by mainly NW-SE trending normal faults that are related to the Afyon-Simav fault system. In this region there are 1 thermal spring and 9 thermal wells with depths of 240 to 650 meters, drilled by governmental agencies and private companies. These waters are used for greenhouse heating and thermal tourism. Temperatures, electrical conductivities (EC) and pH values of the thermal waters changes between 29.3°C and 54.7°C, 587 and 3580 µmho/cm, 6.32 and 7.37, respectively. Thermal waters are of the Na-Ca-HCO3 and Na-Ca-HCO3-SO4 types. The thermal waters in the Heybeli geothermal field are immature waters. The silica geothermometers applied to the thermal waters gave a resrvoir temperature of maximum 115oC. The ä18O-ä2H isotopic data shows that thermal waters of the study area have a meteoric origin, These waters, percolating through the permeable rocks in the recharge area are heated by geothermal gradient and ascend to the surface along the major faults.