The structural and geochronological evolution of the auriferous Santoy shear zone, northeastern Glennie domain, Saskatchewan

English Abstract:

The study area lies within the Pine Lake Greenstone belt of the Glennie domain, 125 km northeast of LaRonge, SK. The Santoy shear zone (SSZ) hosts the Santoy 7, Santoy 8/8 east, and “Santoy Gap” gold deposits. This shear zone was studied using a structural and geochronological (ID-TIMS) approach in order to decipher its complex relationship with plutonism, deformation, alteration and gold mineralization.

Surface and subsurface mapping reveals that the SSZ and deposits therein show a clear structural relationship towards the F₃ Carruthers Lake Synform. The Santoy 7, Santoy “Gap”, and Santoy 8 deposits lie along the western limb of this structure while Santoy 8 east has been reoriented by north trending 45° plunging S folds. The plunges of the ore shoots are parallel to this and coaxial to the plunge of the Carruthers Lake Synform. Appropriately oriented plutonic intrusions acted as structural anisotropies that nucleated shear zones and auriferous fault fill quartz veins along their margins during D_3A dextral reverse oblique slip movement. The age of these intrusions (1874.6±2.9 Ma and 1874.6±1.9 Ma) serves as a maximum mineralization age for these deposits. Geomagnetic anomaly data suggest that a quartz syenite pluton in the area acted as a buttress during D₃ and produced a compressional jog in the SSZ and increased fracture density and fluid flow during mineralization. The age of this intrusion (1807±7Ma) serves as a maximum age for the development of this flexure. Gold mineralization is closely associated with a calc-silicate alteration assemblage. This assemblage occurs synchronously with the main stage mineralization event. Titanite and zircon within this assemblage was dated to 1755±8 Ma indicating Syn-D₃ deposit formation and providing the most accurate age date for gold mineralization in the Glennie domain proposed to date. Beriliferous pegmatite dykes display an F₃ axial planar cleavage and crosscut auriferous zones. An age of 1736.1±1.9Ma for the dyke represents a minimum mineralization age for this system and a new minimum age for regional D₃ deformation in the Glennie domain.