ABSTRACT
Geochemical, environmental isotopes and geophysical data from thermal and cold waters demonstrate the role of combined hydrogeological tools to improve knowledge of the conceptual circulation model of Monção hydrothermal system. Geophysical data show low resistivity zones ascribed to the thermal waters circulation in a granitic environment. The isotope signatures indicate that the aquifer recharge area is located to the south of the Monção Spas, up hill between 300 and 600 m a.s.l. The waters issue at 48°C, and are of Na-HCO3 type. The mineral/solute equilibrium and the geothermometric results show that Monção thermal waters are non-equilibrated due to the high CO2 content. The estimated deep temperatures derived from Na-K geothermometers give the most reliable deep temperatures, in the range of 110 to 126°C. Considering a mean geothermal gradient of 30°C/km at Monção region, the thermal aquifer is between 3.2 and 3.7 km deep.
