Hydrogeochemical Properties of Hot and Cold Waters in Tunceli-Pertek Geothermal Area

The Pertek geothermal area is located near the Singec valley to the southwest of Tunceli and this field has not been previously studied in terms of hydrogeology and geothermal. The dominant rock type in the area is the Permian-Triassic aged Keban Metamorphites which are be limestone and marble. The younger magmatic and sedimentary units (Upper Cretaceous-Pertek Magmatites, Middle Eocene-Upper Oligocene-Kırkgeçit Formation, Upper Miocene-Pliocene-Karabakır Formation and Quaternary-alluvium) have contact with these metamorphics. In addition to the tectonic activity of the region, the dominant lithology of Keban metamorphites (limestone and marble), intra-unit thrust faults and normal faults, shear fractures and cracks increased the porosity and permeability of Keban metamorphics. Therefore, the most important aquifer in the region is the Keban metamorphites and these metamorphites are also the reservoir rock of the hot water in the Pertek geothermal area. The area of feeding of the groundwater in the reservoir rock is located in the north of the Singec valley and the discharge area is in the south of this valley. The feeding field of this reservoir rock is to the north of the Singec valley and the discharge area to the south of this valley. The Pertek geothermal system is an open system, since only limited areas contain semi-permeable sedimentary (Kırkgeçit Formation) and volcanic cover rocks (Karabakır Formation) in the main feeding field. The pH and electrical conductivity of the thermal waters in the system are between 6,18-7,55 and 816-2330 μS / cm respectively. The surface temperatures range from 25.5 to 38.2 ºC. The pH and electrical conductivity values ​​of cold water are between 7.52-8.31 and 402-472 μS / cm respectively. The most common cation in both hot and cold waters is Ca 2+ and the anion is HCO3-. According to IAH (1979) water classification method, hot and cold water, cold mineral water and stream water are of Ca-Mg-HCO3 type, and the lake waters of Keban dam are Ca-Mg-HCO3-SO4 type. Cold spring water is drinkable, but in hot and cold mineral waters the concentration of elements such as Ca, Mg, K, Mn, As and B is above the drinking water standards. The hot waters are generally saturated with calcite, aragonite, chalcedony, quartz and dolomite minerals. Reservoir temperatures are between 74-105°C according to silica and cation geothermometer calculations. According to the enthalpy-silica mixture model, the reservoir temperature is between 80-225 °C and the ratio of cold water mixture to hot water is between 60-88%. According to the isotope analysis, the cold waters in the Pertek geothermal area are shallow, the hot waters are deeply circulated, meteoric origin and respectively modern and sub-modern waters.