Hydrogeochemistry and geothermometry of the Ilgın geothermal field, Central Turkey

The Ilgın geothermal field that is the oldest and most important spa of the Konya Region is located in Central Turkey. The Ilgın geothermal field has five geothermal wells and three hot water springs with flow rates of 40–130 L/s, temperatures 26–42°C and depths of 120–300 m. In the present study, detailed hydrogeochemical investigations are carried out to understand the geothermal energy potential of the thermal waters. The chemical properties of the cold and hot waters collected from the field were determined and the classification and usage possibilities of the waters were investigated. The thermal well water samples have the same Cl, B and Li concentrations in rainy and dry seasons, but those of the other samples are variable in rainy and dry seasons. This suggests the surface water mixtures were constant in hot water wells or that the precipitation times were long. In the Li-Rb-Cs diagram, the Li/Cs ratios of hot waters are 6.53–8.61 in the rainy period and 6.28–8.47 in the dry period, indicating that they are derived from acidic rocks. According to their isotopic composition, it can be said that the waters are of meteoric origin. According to the Langelier, the Ryznar and the Puckorius Saturation Indexes, the waters can precipitate carbonate. The waters interacted with gypsum and anhydrite zones based on the Halite Saturation Index, while the waters are associated with dolomite-rich rocks in terms of the Dolomite Saturation Index. Silica and cation geothermometers except Na-K applicated to the Ilgın geothermal waters yielded similar reservoir temperature estimates (e.g., 13–76°C for rainy period, 10–80°C for dry period). However, reservoir temperature from the other estimates (Na-K geothermometers, enthalpy-chloride diagram and enthalpy-silica mixture model) are higher than 103°C. Taken as whole, the temperature estimates exhibit little agreement between the different geothermometry calculations suggesting that the Ilgın geothermal waters represent immature waters, and water-rock equilibrium in the geothermal reservoir was not fully attained.