Geochemistry of thermal springs, Alhama de Granada (southern Spain)

The waters of the thermal springs at Alhama de Granada vary in temperature between 27 and 45°C. Temporal changes in the composition of the principal spring (Baños Viejos) indicate that a small degree of mixing may occur between deep thermal waters and shallow groundwater. Slight compositional variations also occur between the various thermal springs in the study area. These spatial variations are due to the different local hydrodynamic conditions in the springs. Towards the north in less hydraulically transmissive rocks, cooling of the rising water is more noticeable, as are ion exchange and processes of SO4 reduction. The chemical composition of the water is related to the dissolution of evaporites (SO4 and Cl salts), carbonates and silicates, and to the possible existence of sources of S within the rock. Estimates of the mean residence times have been obtained based on 14CDIC and T. The state of thermodynamic equilibrium at the spring discharge was calculated using the SOLMINEQ.88 program. The results indicate that all the samples are supersaturated with respect to quartz, chalcedony, cristobalite, calcite, aragonite and dolomite, and undersaturated with respect to gypsum, anhydrite and halite. The use of different geothermometers and modelling of saturation indices for quartz, albite and anhydrite indicate temperatures of about 110°C.