The Beacon mine is a vein-type gold deposit hosted by the granodioritic Bourlamaque pluton, a syn-volcanic intrusion crosscutting Archean volcanic rocks of the Val-d'Or Formation.  An E-W trending, moderately north-dipping (50-65 deg.) brittle/ductile fault system (e.g. the Beacon fault) is found at the Beacon mine.  It consists of highly chloritized zones, characterized by a phacoidal foliation.  Barren milky quartz veins, up to 5 meters wide are found in close association to these faults.  On the property, the Beacon fault separates two distinct structural domains :  i) a south domain defined by the presence of ENE-WSW trending, steeply south-dipping (70-85 deg.) reverse mylonitic shear zones (e.g. the Leroy shear system) that steepen with depth and ii) a north domain defined by NE-SW trending, sub-vertical to very steeply north-dipping (>85 deg.) mylonitic shear zones. Two hypothesis are proposed to explain the coexistence of these shear zones :  i) they are both part of a conjugate fault system, or ii) the mylonitic shear zones in the north domain correspond to the deeper parts of the same mylonitic system, uplifted by the Beacon fault.

Auriferous mineralization is restricted to the south domain where four distinct Leroy-type mylonitic shear zones are crosscutt by more slightly south-dipping (30-45 deg.) reverse breccia veins.  These mylonitic shear zones are up to 1.5 meters wide and contain foliation-parallel laminated fault-fill veins that show a Qz-Cb±Py paragenesis, as those of the north domain.  The crosscutting breccia veins, which are restricted to the south domain, are less than 1 meter wide and show a Qz-Cb-Tm-Py-Au±Cl assemblage, suggesting a more evolved hydrothermal fluid.  For this reason, it is proposed that gold mineralization in the Beacon mine is related to this breccia vein system.

The orientation and structural characteristics of mylonitic shears and brittle/ductile fault zones of the Beacon mine are representative of large-scale tectonics in the Val-d'Or mining camp.  Mylonitic shear zones and breccia veins are, respectively, interpreted to be second- and third-order structures to the Cadillac Tectonic Zone.