Saraykent ve Akdağmadeni (Yozgat) Sıcak ve Mineralli Sularının Hidrojeokimyasal ve İzotopik İncelemesi

Abstract

The study aimed to construct a conceptual hydrothermal model of the geothermal system in Saraykent and Akdagmadeni Geothermal Areas. In this context, the physical, hydrogeochemical, isotopic properties of the waters in the area as well as the geological and hydrogeological properties of the area were investigated. Thus, the geothermal system was tested to determine the areas of recharge and circulation mechanism. The study area covers the Saraykent and Akdagmadeni Geothermal Areas in Yozgat province. The Paleozoic-Mesozoic metamorphic rocks of the Kirsehir Massif (gneiss, schist, marble) are the basement rocks of the study areas. The major geothermal reservoirs in the study areas occur in the Eocene aged volcanic rocks which have local fracture and fault zones and excessive tectonic deformations. The cap rocks of both areas are composed of Eocene tuff and clay and marl sedimentary, and metamorphic rocks (particularly schist). Water springs and geothermal wells are located within the study areas. In the Saraykent geothermal springs periodic discharge temperature range from 48.2 to 76.2 °C, whereas in the Akdağmadeni geothermal springs periodic discharge temperature range from 26.0 to 47.7 °C. The cold water samples are classified as Ca+2-HCO3- types, whilst geothermal water samples are classified as (Na++K+)-Cl--SO4-2 and (Na++K+)-SO4-2-Cl- types. The hydrogeochemical and isotopic contents of the water samples in the study area vary according to local and lithological characteristics. A comparison of the Saturation Index (SI) calculations of geothermal waters with the minerals content of the scales from geothermal wells, revealed that the geothermal waters have calcite and quartz saturation and thus are scale-forming. The local meteoric water line of the Saraykent-Akdagmadeni Area has been determined as δ2HH2O=8.25*δ18OH2O+17.90 (R2=0.99). Both cold waters with hot and mineral waters are meteoric in origin. The hot and mineral waters compared to the cold groundwater have lower δ18OH2O, δ2HH2O and 3H isotopic values that suggest higher recharge elevation and longer residence times (more than 60 years) of hot water in the geothermal reservoir. It is estimated that the probable elevation areas of recharge calculated for δ2HH2O content in hot and mineral waters in both geothermal areas are between 1623 to 1975 m for Saraykent Geothermal Area and 1768 to 1905 m for Akdagmadeni Geothermal Area. These values correspond to the southeast of the study area and the elevations of the Akdagmadeni Horst, which consists of metamorphic rocks (marble, schist). It shows that the δ13CDIC isotope values in geothermal fluids may have originated from the dissolution of freshwater/marine carbonates. These geothermal springs were determined to have originated from volcanic/sedimentary sulfur and evaporites (gypsum etc.) belonging to Central Anatolian Group of Middle Miocene-Pliocene, according to the δ34SSO4 isotopic value of hot and mineral waters in the study areas. The total alpha and total beta values in water samples taken from Saraykent geothermal waters are higher than other water samples in Akdagmadeni Area. This might be related to granitic intrusions and rhyolitic volcanics in the Saraykent area. For reservoir temperature, average values were calculated with silica and isotope geothermometers; It was concluded that a reasonable expectation would be around 130 ºC in Saraykent Geothermal Area and around 120 ºC in Akdagmadeni Geothermal Area. The conceptual hydrothermal model of the studied area is created by the updated geological-hydrogeological data in the studied areas and detailed hydrogeochemical, geochemical and isotopic data collection and evaluation.