The Balcova field is located 9 km west of izmir City, Turkey. The Balgova geothermal field has been studied by many researchers and their studies have also guided this work. However, this paper addresses the structural, hydrogeological and geochemical properties of the field and their relationship to its geothermal potential. The compositions of water samples collected from the deep wells and cold groundwater resources have been classified by using the computer program "Aquachem 3.70". Two different groups of waters as hot and cold ground water samples were analyzed and 10 different types of hot water and 3 different types of cold water were determined. Cutting samples and cores from selected depths have been studied by petrography and three zones of hydrothermal alteration have been determined. These are: a montmorillonite + kaolinite zone (100-200 degrees C), a transition zone (150-200 degrees C) and a chlorite + illite zone (200-250 degrees C). The calculated reservoir temperatures by using chemical geothermometry applications range from 104 degrees to 260 degrees C. Hydrothermal alteration mineral assemblage of the geothermal field may reflect an acid-alkaline equilibrium of the geothermal system, besides indicating the likely extent of the geothermal system. (C) 2015 Elsevier Ltd. All rights reserved.