Résumé
A tectonic study of the Millas granite was conducted to characterize the development and the geometry of its fracture network. Analyses of the fracturing and in particular of the fracture fillings, from corings on the Montalba site, show the hydrodynamic role of each fracture set and indicate the conductive direction to be NE-SW. These results give the main clues to the understanding of tracer flow-paths between bore-holes and demonstrate the necessity of a methodical approach to the fracturing for any modelling of mass transfer in a basement aquifer.