Los sistemas geotermales del Pirineo Central. II. Resultados de la aplicación de técnicas geotermométricas

Abstract

Reservoir temperatures are calculated for six geothermal systems in the Central Pyrenees (Arties, Caldas de Bohí, Benasque, Panticosa, Luchon and Cauterets) using different geothermometrical methods. In general, the selected hot springs have similar geochemical features belonging to the group of alkaline thermal systems installed in granitic environments. More in detail, however, it is important to note that Na and K concentrations of Panticosa and Benasque thermal springs are the lowest found in this water group to date.
Both classical geothermometers and modeling calculations agree within a few degrees for the Arties, Caldas and Luchon geothermal systems: thermal waters are in equilibrium in their reservoirs with a common mineral association (quartz, albite, K-feldspar, caolinite and some calc-aluminum silicate) at 103, 107 and 127° C, respectively. Cauterets, Panticosa and Benasque thermal waters appear to be equilibrated with the same mineral association at 98, 107 and 94° C, respectively as deduced from silica and Na-K geothermometers. Na-K-Ca and Ca-K geothermometers provide lower temperatures for these systems, probably because of some exchange of calcium between rock and water during the ascent of solutions.
Nevertheless, the modeling calculations fail to represent the composition of Panticosa and Benasque thermal springs: these waters are out of equilibrium with the selected mineral association at the temperatures given by Na-K and SiO₂-quartz geothermometers Therefore, the agreement between these geothermometers appear to be fortuitous, specially for Benasque thermal waters.