New geological mapping (1:10.000 scale) and structural analysis in the Orco valley (NW Italian Alps), give insights on the post-metamorphic brittle tectonic evolution of the Gran Paradiso Unit and adjoining Piemonte Ophiolitic Unit and Sesia-Lanzo Unit. According to existing geochronological data, the metamorphic evolution of the studied domain ended in Early Oligocene and was followed by a progressive exhumation during Neogene. This work describes the brittle fault network developed during the post-metamorphic tectonic stages coeval to exhumation. The geometry and kinematics of this fault network allow to interpret the study area as a part of a larger lowstrain, fault-bounded block, whose main bordering discontinuities are located outside the mapped region. The post-metamorphic kinematic evolution was characterised by: (a) ESE-WNW extension, attested by NNE-SSW normal faults and extensional joints; (b) dextral shearing along a major E-W shear zone (Orco shear zone). The individual faults of the studied area are considered as P-or R-shears of the Orco shear zone, which could be in turn a part of a larger NE-SW regional shear zone bounded to the N by the Chamonix-Rhône-Simplon Line. Résumé Le travail de cartographie à l'échelle 1:10.000 et une analyse des éléments

The growing industrial minerals demand, in the perspective of a sustainable development of mining activities, implies a strong orientation to underground operations in the near future. In complex geological areas, for the definition of a reliable 3D ore body model a methodological approach, aimed to improve geological and geotechnical model reliability allows a confident mineral deposit evaluation and a reliable mine design, or, in other terms, costs reduction, safety increase and mining project sustainability. The described method finds its maximum application in complex geological and structural contexts, such as the Valmadonna-Pedemonte “Marmorino” quarry.

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