Geochemical and Isotopic Characteristics of the Balikesir Thermal Waters, Turkey

Abstract

The Balıkesir geothermal waters in northwestern Turkey are represented by discharge temperatures in the range of 32-99ºC and TDS contents between 327 and 2578 mg/l. The waters in the region are of Na-SO4, Na-HCO3 and Ca-HCO3 type character. It was determined that the solubility of silica in most of waters is controlled by the chalcedony phase. Equilibrium states of the Balıkesir thermal waters studied by means of the Na-K-Mg-Ca diagram, mineral saturation calculations and activity diagrams approximate a reservoir temperature of about 120ºC. Most waters are found to be equilibrated with calcite, chalcedonyquartz and muscovite at predicted temperature ranges similar to those calculated from the chemical geothermometers. 18O-D compositions clearly indicate a meteoric origin for these waters. 34S contents of sulfate in thermal waters ranging from -5.5 to +25.2‰ correspond to nonmarine evaporates while sulfur in some others is derived from the sulfate reduction process. 13C composition of dissolved inorganic carbonate in waters is between -17.7 and +0.7‰. Carbon in high-temperature waters is thought to have originated from dissolution of marine carbonates. On the contrary, carbon in low-temperature waters is derived from an organic source.