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Geochemical features and geothermometric modeling of les Escaldes geothermal system (Andorra)

Abstract:

The geochemical characteristics of the thermal waters from Les Escaldes (Andorra) are similar to other geothermal systems in the Pyrenees, belonging to the group of granite-related alkaline thermal waters (high pH, low total dissolved solids, very low magnesium concentration, and sodium as the dominant cation). Because of the high pH of these waters (pH=8.95), they have a very low CO 2 partial pressure, and silica is partially ionized as H 3SiO 4-. We have carried out a geothermometric modeling exercise taking into account kaolinite re-equilibrium during the ascent of these thermalwaters. Results showthat thewaters are in equilibrium with albite, K-feldspar, quartz, kaolinite and some calcium-aluminosilicate at a temperature of 90±10°C in the reservoir. The pH increases at a rate of 0.0125 pH-units/°C during ascent; the rate is not affected by the kaolinite re-equilibrium process, and it depends on the active acid-base pairs present in the thermal waters. © 2007 Taylor & Francis Group, London.