Hydrogeological and hydrocemical investigation of Hayran (Alucra-Gi̇resun) geothermal water springs

Hayran geothermal water spring is located in Alucra district, 127 km southeast of Giresun province. The temperature of the geothermal water in the field is 24.6-28.1°C, pH is 6.47-7.48 and EC value is 592-646 µS/cm and the water is Ca-Mg-HCO3. In the study area, there are sedimentary units with volcanic intercalations that were deposited in times ranging from Early-Middle Jurassic to Quaternary. In the Hayran geothermal field, isotopic (O, H) characterization of water and surrounding rock properties were used to define the geothermal system and determine the elements of the system. For this purpose, hydrochemical and isotopic characterizations of samples taken from geothermal and cold springs and surface waters were determined. It has been determined that all waters in the Hayran geothermal field are saturated with carbonate minerals such as calcite, aragonite and dolomite, iron minerals such as goethite and clay minerals such as K-mica and kaolinite. Concentrations of trace elements Al, Mn, Cu, Sr, Ba and Pb in water are higher than other elements. HK cold spring water is above the standards in terms of Fe (270 µg/L) and As (14.7 µg/L) concentrations. Stable isotopes (δ2H and δ18O) and tritium data show that geothermal spring (ASK) water is water of deeper circulation and meteoric origin recharged from higher elevations. The reservoir temperature of the geothermal fluid was calculated as approximately 28.2-53.6 °C with silica geothermometers and 115.16 °C according to the silica-enthalpy mixture model. With these temperatures, Hayran geothermal field is in the "low enthalpy field" class. Keywords: Hayran Geothermal Field, Geothermal System, Hydrogeochemistry, Environmental Isotopes, Alucra