Joleen Belanger, MSc

J. Belanger¹, D. Tinkham¹, B. Lafrance¹, S. Brueckner¹, J. Simmons¹, M. Laverge¹, W. Boehme¹, J. Ordonez-Calderon^2 
1Mineral Exploration Research Centre, Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario, Canada, 
²Kinross Gold Corporation, Toronto, Ontario, Canada 

The Great Bear deposit, located ~25 km SE of Red Lake, Ontario, lies within the Uchi Subprovince of the NW Superior craton. It is host to Au mineralization in polydeformed Archean volcanic and sedimentary rocks previously suggested to have reached greenschist to lower amphibolite facies metamorphic conditions. The property is divided into a distinct northern felsic domain and southern mafic domain that are separated by a SE-striking crustal scale LP Fault. A ~500m wide, NW-SE trending high strain zone, termed the LP Fault Zone (LPFZ), sits within the felsic hanging wall of the fault. This project focusses on constraining the metamorphic evolution across the property by: (1) calculating the P-T conditions of observed mineral assemblage development; (2) discerning any metamorphic discontinuities across interpreted structures; (3) documenting and modelling metamorphic fluid production or infiltration, and (4) determining if the rocks experienced polymetamorphism (overprinting metamorphic events). 

Core logging and petrographic analysis of metamorphic mineral assemblages and reaction textures across the deposit were performed to determine relationships between the variability of metamorphic conditions and fluid production, deformation fabrics, and alteration. Low variance metamorphic mineral assemblages in the felsic domain are characterized by a quartz + white mica + biotite matrix with intertectonic garnet staurolite andalusite porphyroblasts, indicative of middle amphibolite facies metamorphism. Staurolite porphyroblasts locally contain inclusions of garnet, and andalusite porphyroblasts overgrow both staurolite and garnet. These middle amphibolite facies assemblages and paragenesis in the felsic domain indicate metamorphism reached temperatures where andalusite forms after staurolite and indicate a high temperature-low pressure metamorphic P-T path. These low variance assemblages are concentrated within the zone of high strain along the LPFZ, and the number of observed porphyroblast phases co-existing and abundance of andalusite decreases towards the NW and SE. This assemblage variability suggests a decrease in metamorphic grade towards the northwest and southeast regions of the property, and phase equilibria modelling will be used to confirm this interpretation. 

Mafic domain metamorphic assemblages contain calcic amphibole, quartz, plagioclase, and biotite, with local prograde chlorite parallel to the dominant foliation, widespread retrograde chlorite, and local discontinuous intervals containing garnet porphyroblasts. Facies identification and determination of peak metamorphic temperatures in the mafic domain will be determined using mineral chemistry of amphibole and feldspar coupled with phase equilibria modelling of individual samples. These results will be compared to the P-T constraints of the felsic domain to determine if there is a metamorphic discontinuity across the LPFZ.