Water Chemistry and Isotope Studies In Aksaray Geothermal Fields (Acıgöl-Ziga-Şahinkalesi), Central Anatolia, Turkey

Abstract

The basement in the study area is comprised of gneisses of Paleozoic Tamadaq formation, marbles of Bozcaldag formation and Upper Cretaceous Baranadag granitoid intrusion into the above-mentioned rocks. These units have unconformable relations with Lower Eocene Cayraz formation and sedimentary rocks of Upper Eocene - Lower Miocene Mezgit group. All these units are unconformably overlain by Middle Miocene- Quaternary tuffs, ignimbrites with sedimentary intercalations and rocks of Cappadocia Volcanic belt represented by tuffites with sedimentary interbedding, basaltic lavas, volcanic ashes, pumice, dacitic-rhyodacitic lava domes. The study area contains Ziga and AClgol (Narkoy) thermal fields which have a temperature of 44-65 °C from wells and hot springs. Hydrothermal alterations surrounding the geothermal area; young volcanic and tectonic activity, and the hot springs are the surface manifestation of the geothermal possibilities in the area. Reservoir rocks of the geothermal system are Paleozoic gneiss, schist and marbles. Cap rocks of the system in the study area are hydrothermally altered tuffs and ignimbrites. According to the classification of IAH (International Association of Hydrogeologists) standards while; all of the cold waters are Ca-Mg-HCO3 and CaHCO3 type in the region, the hot waters of the Acigol field are classified as Ca-Na-HCO3-CI type and mineralized hot waters, the hot waters in Ziga field are classified as Na-CI-HCO3 type and B bearing mineralized hot waters, the hot water of Sahinkalesi field (from well) is classified as non-mineralized thermal water. Deuterium results suggest 1500-1600 m recharging elevation for hot springs and water chemistry and isotope studies imply that recharging area may extend up to the foothills of the Hasandaq. Tritium analyses have revealed that the hot water was recharged from precipitation before nuclear tests experienced before 1952 (I.e. older than 60 years). According to SiO2 - enthalpy mixing model, 155°C reservoir temperature and 65% cold water mix were calculated for AClgol field. On the basis of chalcedony geothermometer, 114-160°C, 69-93 °C and 135°C and on the basis of quartz geothermometer 140-181 °C, 99-121 °C, and 159°C reservoir temperatures were calculated for Acigol, Ziga and Sahinkalesi geothermal fields, respectively.