Présentations Colloques

    Oral Presentation
    Session 8.08: Mineral and Thermal water: an indicator of deep processes and source of economically valuable minerals
    Alazard Marina
    Hydrogeological conceptual model of a crystalline thermo-mineral carbo-gaseous aquifer driven by a weathering profile and tectonic fractures
    Thermo-mineral and carbo-gaseous systems are associated to specific geological structures, such as faulted and fractured bedrock, allowing the upward circulation of deep hot mineral fluids and or gases. Although conceptual models based on groundwater flow through faults and tectonics fractures can be relevant, the 3-D extension and hydraulic properties of such aquifers exploited either for bottling or spas are rarely considered. Moreover, faults are not always conductive structures and in many cases, they can constitute impervious boundaries due to compressive tectonic activity, clogging or recrystallization, etc. **Here we develop a comprehensive research based on various approaches (i.e. geological, geophysical, hydrodynamic, geochemical and modelling). The converging results allow conceptualizing the functioning of the carbo-gaseous aquifer system of the Saint-Galmier (France) natural mineral water, located along major border faults of an Oligocene graben. **Based on seismic profiles, geological observation (outcrops) and more than 200 boreholes, a 3-D geological and structural model has been build up. Conceptual and numerical modeling of the system was based on 36 pumping tests data, piezometric and chemical surveys, and more than 80 punctual samples for groundwater and surface water chemistry and isotopy. **Such a density of information is rarely equaled in complex context. Several approaches highlight the significant role of the fissured layer of an ancient weathering profile on the hydrogeological properties, spatial extension and compartmentation of this typical mineral carbo-gaseous aquifer system. Numerical hydrodynamic modeling has been performed on one aquifer compartment because of high density data. It notably allowed estimating the location of the deep fracture feeding the granitic aquifer with deep fluids and allowed a good assessment of mixing rates between deep waters and water from the fissured layer. **


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