| Abstract |
The Salihli geothermal fields are located in the southern part of the Gediz Graben, which is one of the Western Turkey grabens. Salihli geothermal systems have been physically divided into four main groups; the Sazdere, Kursunlu, Caferbeyli and Sart-Camur geothermal fields. The reservoir rocks of the geothermal systems are karstic marbles and fractured metamorphic rocks belonging to the Mesozoic Menderes Massif, which is basement in the study area. Since the clayey levels of the overlying Neogene Gobekli and Acidere units have very low permeabilities, they are the cap rock of the systems. Heat sources may be magmatic intrusions closed to surface, rising along the young faults caused by graben tectonism. As with many other geothermal systems in Western Turkey, all the thermomineral waters in the study area are of meteoric origin and circulation in these systems is closely related to tectonic activity. Most of the thermomineral waters in the study area are of the sodium bicarbonate type. Cold waters in the area are mainly dominated by Ca2+, Mg2+, and HCO3 ñ ions, and often have no dominant cation or anion. The major hydrogeochemical processes for thermomineral waters in the geothermal fields are ion exchange between Na+ and Ca2+ and/or Mg2+ cations, which are also called natural water softening reactions. The thermomineral waters of the study area fall mostly into the Ca2+ and Mg2+ montmorillonite fields and partially the kaolinite and K-feldspar fields on the activity diagrams. The waters are mainly undersaturated with respect to carbonate and sulfate minerals. One important environmental problem in the study area is boron contamination in aquifers and soils. The presence of boron is attributed to the geothermal systems of the study area. To prevent boron contamination of cold waters used for irrigation in the study area, re-injection of produced thermomineral waters into the geothermal reservoir is necessary. Assessments of empirical chemical geothermometers and mixing models applied to the thermomineral waters, which have measured discharge temperatures ranging from 37oC to 155oC, suggest that reservoir temperatures vary between 150oC and 230oC. Due to the fact that these waters are not in equilibrium with reservoir rocks, and are probably dominated by a combination of mixing phenomena, rock dissolution and ion exchange reactions, the geothermometer results should be considered tentative. |