Les eaux thermales des granites de Galice (Espagne): des eaux carbogazeuses aux eaux alcalines (Thermal waters from granites of Galicia (Spain): from CO 2-rich to high-pH waters)

Abstract

Thermal waters from Galicia, Spain, range from CO 2-rich, low-pH to high-pH, sulfide-rich waters, going through intermediate waters. In order to explain the variations of their chemical composition, we present a discussion of the major factors governing the water composition. We eiscuss especially the isochemical recrystallization of a granite. It is shown that the equilibrium mineral association of the water-alkali granite system is unique. For chalco-alkaline granites, two different associations are possible, depending on the chemical composition of the granite. The effect of an addition of CO 2 is also discussed. Some criteria allowing a distinction between fully equilibrated and non-equilibrated waters are presented. Finally, the composition of Galician waters is explained by different initial CO 2 contents and by different values of the degree of the granite-water reaction progress (ξ).