Présentations Colloques

Oral Presentation
Session 8.08: Mineral and Thermal water: an indicator of deep processes and source of economically valuable minerals
Selas Bertrand
Multi-tracer groundwater dating (CFCs SF6, Tritium and 14C activities) for the characterization of a thermal flow system the case of the Avene-thermal spring
Thermo-mineral water is characterized by its constant physicochemical properties with time, which is most often a consequence of deep GW flow paths and long residence time. These characteristics result from complex and relatively unknown geological settings. Understanding the origin and transfer of the thermal water is however a key factor to implement a sustainable management of the resource.**In this context, the objective of this geochemical study was to build-up a conceptual model of GW recharge and transfer for the Avène thermal system based on the assessment of residence time at various outlets of the aquifer. The Avène thermal spring (25°C) is located along the North part of the Montagne Noire, about 50km Northwestern from Montpellier, France. The main questions were focused on a hypothetic role of deep CO2 fluxes on the GW chemistry, and on the GW transfer from the recharge area to the thermal outlets as compared to other non-thermal karst springs emerging from the same geological unit. **The approach is based on the use of historic and new tritium, 13C and 14C activities data, and also dissolved gases (CFCs SF6) to constrain a lumped model.**Results show that the thermal GW is flowing in depth through the Cambrian dolomites without deep CO2 contribution, and that an exponential model can explain the calculated residence times for the thermal GW. GW sampled in thermal wells can actually be interpreted with a unique GW flow path showing various degrees of evolution or interaction with non-thermal karst, but with a constant physicochemical composition.**This conceptual model can now be used as a reference state of the system for future investigations.