Hot spring waters of the La Selva geothermal system show high concentrations of Cl, F. Ca, Na, K, Li, Si, As, Ba, and Rb. whereas cold waters show low salinity, high concentrations of NO(3), and significant As content when mixed with geothermal waters. Modeling of the geothermal fluids indicates that the fluid is supersaturated with aragonite and calcite, which matches the travertine precipitation close to the present discharge areas. Moreover, the barite and fluorite are also are near equilibrium levels, indicating possible control of Ba and F solubility by these mineral phases, which also precipitate in some discharge areas. Likewise, the fluid is supersaturated with respect to quartz, indicating the possibility of siliceous precipitation near the discharge areas of the present geothermal fluids. Taking into account the Na-K, Na-K-Ca, and SiO(2)-temperature geothermometers, the temperature of the reservoir may be estimated to be about 135 degrees C. The chemistry of the geothermal fluids has changed from a recent high-enthalpy system, which precipitated siliceous deposits, to the present low-enthalpy system, which precipitates carbonated deposits (travertine). Multivariate analysis of the groundwater shows high correlations between K, Ca, As, Br, Ag, and Ba, suggesting that As is introduced to the environment via geothermal fluids. Moreover, As concentrations in hot groundwater are associated with high concentrations of Li and Si, as has been observed in other geothermal fields. Metal concentrations in the hydrothermal deposits show high values of Ag, As, Ba, Pb, Sb, and Zn, mainly in the siliceous deposits of the town of Caldes de Malavella, where the geothermal system deposited materials with high As concentrations (123-441 ppm). The similarities between the geochemical characteristics of the hydrothermal deposits and the groundwater suggest that the metals in these deposits and fluids have the same origin. (C) 2011 Elsevier Ltd. All rights reserved.