Geochemical assessment of Simav geothermal field, Turkey

In this study, geochemical methods are used to reliably analyze and understand the Simav geothermal field whose thermal water is rich in terms of Na-HCO₃-SO₄ and is affected by groundwater which is low in Cl. The water is of meteoric origin and belongs mostly to the immature water group. Quartz and Na-K geothermometers are used to calculate the reservoir temperatures as 70-195 °C and 167-249 °C, respectively, and the Na-K-Mg geothermometer indicated temperatures of approximately 230-240 °C. The isotopic evaluation of the geothermal system indicates that the water in the Simav geothermal reservoir is ¹⁸O enriched is fed by cold water from Nadarçam and that the age of the water is older than 50 years. The alteration mineralogy of the field points out to reservoir temperatures between 160 °C and 250 °C in the thermal water. The activity diagrams of the thermal water indicate the existence of fluid-rock interaction and show that the water is in equilibrium with K-feldspar, muscovite, albite (Na-feldspar), Mg-chlorite and epidote minerals at a temperature range of 150-250 °C. The activity diagrams also point to a potential source that might be located in a deeper zone that is hotter than the reservoir currently used for production, which is consistent with the alteration mineralogy of the field and Na-K geothermometers. The mineral equilibrium diagrams yield reservoir temperature values that are in harmony with the values obtained from the production zone and silica geothermometers. According to the mineral equilibrium diagrams, it is probable that calcite precipitates at high temperatures and that silica precipitates at low temperatures.