Hydrochemical and isotopic studies in Aksaray geothermal fields central Anatolia, Turkey

The studied area is located at eastern part of Aksaray province in Central Anatolia. The basement rocks of studied area is Paleozoic aged Bozcaldag formation composed of marble, schist and gneiss and Cretaseous aged granitoid intrusion intrude within these basement rocks. These rock units are overlain uncomfortably by middle miocene to Quaternary aged volcanic rocks of Cappadocian volcanic belt interlayer sediments. The compositions of these units are mainly represented by tuff, ignimbrite, reworked tuff interlayer sediments, basalt lavas, ash fall deposits, pumice and dasite to rhyodasitic lava domes.The study area contains Ziga and Acigoel (Narkoey) thermal area, which they have similar geologic environments with in the Cappadocian volcanic belt of the Tertiary to Quaternary age. Existence of surface manifestation like that high regional heat flow, the presence of expanding acidic to weakly acidic hydrothermal alteration surrounding the geothermal area, hot springs which have a temperature of 44-65 degrees indicating the important of geothermal possibilities in the area. Water chemistry studies have been carried out on 34 water samples to estimate relation between hot and cold water, calculate reservoir temperature using geothermometre and mixing models, hydrological isotope studies were carried out to on 10 samples to clarify extending of recharging area and travel time from recharging area to discharging area. Water analyses results were assested using some diagram such as Fournier Cl-Entalphy, SiO2-Entalphy, Langelier- Ludwig, Piper, schoeller etc to classify them. Water-rock interaction have been tried to be define on the base of these result.On the base of water chemistry analyses, all of the cold waters are Ca-Mg-HCO3 and CaHCO3 type. the hot waters in Ziga field classified as Na-Cl-HCO3 type and As and B bearing mineralized hot water. Geothermal fluids in Acigoel field, classified as Ca-Na-HCO3-Cl type and B bearing mineralized hot water, and Þahinkalesi hot water(from well) has been classified as Ca- Na-HCO3 type non mineralized thermal water. According to Giggenbacch 1988 the hot waters are immature in the Aksaray region so silica thermometers have been carried out in the area. The rate of mixing cold water has been found as % 81and based on the Cl-entalphy and silica- entalphy mixing models. These models showed 188degreesreservoir temperature in the studied area. Although Acigoel thermal waters fall on mixing line, Þahinkale hot waters waters make a schift from the mixing line with related Cl enrichment and Ziga hot waters represent conductively cooled and/or evaporite related chloride enrichment. When Deuterium result belong to water samples which collected from different elevation plotted versus elevation, 'Deuterium = -0.0016x(yükseklik) - 74.127' trending line, was found as elevation trending line. When the Deuterium result of hot water sample colected from Acigoel area were put in this equation, recharging elevation has found as 1414m. Similarly, recharcing elevation was found as 2100-2200m in Þahinkalesi and above 3000m for the Ziga field, This elevation trending has showed that recharging area of the fields may reach to Hasandað and also, iso-Cl and SiO2 concentration map of the hot and cold Water sample collected from the area supported this idea. It has found that either O18 and Deuterium enrichment in some samples may be the reason of surface evaporation effect when being fed. It has been shown that shift from local meteorik water line through to right at hot water samples belonging Ziga and Acigoel fields. This situation refers these waters has deep sirculation so, has enriched about heavy isotops (O-18) with respect to water-rock interaction. It has been shown that All of the hot water samples collected from the area has between 0-2 TU. So It can be say that these water samples has been fed from the precipitation before 1952. Other waters samples which have effected from the precipitation after nuclear experience with 2-7.75 TU. So they have interpreted as mixing water with young water old water. As it was seen that The shallowest sirculation water are Þahinkalesi cold waters according to Tritium versus O18 graffic. Water samples are arrenged from having shallow sirculation through the deep sirculation Þahinkalesi, Helvadere, Ziga and Acigoel cold water respectively with respect to Tritium-EC graffic. For the thermal waters, Sahinkaelesi thermal water has the shallowest sirculation water with lowest EC and Acigoel and Ziga thermal waters have represented deep sirculation Waters with high EC and O18 rate. 188 degreesreservoir temperature have calculated. According to Cl-enthalpy and SiO2 -entalphy mixing models On the basis of silica thermometer (Fournier 1977) 119-145#degree#, 160-181degreesand 135-159degreesreservoir temperature have been calculated in Ziga, Acigoel and Sahinkalesi geothermal fields respectively