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 degreesC. Temporal changes in the composition of the prin cipal spring (Banos Viejos) indicate that a small degree of mixing may occu r between deep thermal waters and shallow groundwater. Slight compositional variations also occur between the various thermal springs in the study are a. These spatial variations are due to the different local hydrodynamic con ditions in the springs. Towards the north in less hydraulically transmissiv e rocks, cooling of the rising water is more noticeable, as are ion exchang e 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 C-14(DIC) 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, cristobalit e, calcite, aragonite and dolomite, and undersaturated with respect: to gyp sum, anhydrite and halite. The use of different geothermometers and modelli ng of saturation indices for quartz, albite and anhydrite indicate temperat ures of about 110 degreesC. (C) 2001 Elsevier Science Ltd. All rights reser ved.