Geochemical characterisation and modelling of the Luchon hydrothermal system (Central Pyrenees, France) and lessons learnt for the use of geochemical modelling techniques in granite-hosted alkaline thermal waters

Alkaline hydrothermal systems hosted in granitic rocks have been extensively investigated as natural analogues for radioactive waste disposal and the geological storage of CO2. Thereby, their geochemical characterisation provides useful information long-term performance assessment predictions. The modelling one these alkaline has performed Luchon (France), together with application different geothermometrical techniques to determine temperature, pH mineral equilibrium conditions at depth. results show that main processes controlling hydrogeochemical evolution this system are: (1) mixing between deep thermal cold surface waters, (2) conductive cooling (3) external input Other important are most waters characterised by a high pH-buffering capacity during processes, values characterise not only inherited from reservoir but strongly enhanced cooling. temperature predicted is range 117 ± 8 °C, good agreement temperatures ranging 108 133 °C classical geothermometers. calculations indicate well solutions reached quartz, albite, potassium feldspar, zoisite prehnite, re-equilibirum kaolinite calcite ascent surface. Another outcome precipitation could take place CO2 trapping mechanism similar systems. Further, sharp influence on reveals susceptibility potential contamination processes.