Taylor Mugford, MSc

The Macassa mine, one of the world’s highest grade gold mines, is located in the Kirkland Lake Gold Camp (>24 Moz gold) of northeastern Ontario within the southern Abitibi greenstone belt. Gold mineralization is hosted by orogen-parallel reverse brittle faults, which cut through siliciclastic sedimentary and alkalic volcanic rocks of the ca. 2676 Ma-2670 Ma Timiskaming assemblage and co-genetic intrusions. These rocks are separated from older mafic and komatiitic volcanic rocks of the ca. 2705 Ma Larder Lake Group by the Larder Lake-Cadillac deformation zone (LLCDZ), a 50 m-200 m wide ductile deformation zone hosting several world-class gold deposits over its 250 km strike length across eastern Ontario and western Quebec. 

Current gold production is mainly from the South Mine Complex (SMC), a network of east-northeast trending, shallowly dipping faults filled with quartz veins, hydrothermal breccia, sericite and pyrite alteration. The SMC is bounded by the steeply south-dipping, south-side-up reverse, Main Break to the north and the steeply north-dipping, north-side-up reverse, Amalgamated Break to the south. This study focuses on a 2,300 m wide panel of Timiskaming volcanic and sedimentary rocks between the Amalgamated Break and the LLCDZ to the south. The Amalgamated Break overprints weakly deformed Timiskaming rocks, with ductile strain increasing towards the LLCDZ. Stratigraphy is folded and transitions from south-younging near the LLCDZ to east-younging further north. The earliest and most penetrative foliation is a steeply (70-90°) south dipping and east-northeast striking S₂ foliation, which is axial planar to the folds. The S₂ foliation becomes more pronounced along the LLCDZ where it is parallel to bedding. A steeply plunging stretching lineation and intense carbonate alteration further characterize the LLCDZ.  The S₂ foliation is locally overprinted by a northeast-striking, steeply (70-90°) south dipping, S₃ cleavage, which is associated with Z-shaped F3 folds and formed due to dextral reactivation of the LLCDZ. 

Preliminary results suggest that the Amalgamated Break evolved from a brittle fault to a ductile shear zone due to clay alteration during fluid flow along the fault. A mineralized zone within the panel, i.e. the AK zone, is controlled by brittle fractures and breccias, predating the regional S₂ foliation. This suggests that mineralization is associated with a brittle deformation event that predates the formation of the LLCDZ. The project aims to further investigate the timing relationships between the mineralized brittle faults (Amalgamated Break and Main Break) and ductile LLCDZ and structural controls on gold mineralization.