Joleen Belanger, MSc
J. Belanger1, D. Tinkham1, S.M.Brueckner1, B. Lafrance1, J. Simmons1, M. Laverge1, W.H. Boehme1, J.C. Ordonez-Calderon2
1Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario, Canada
2Kinross Gold Corp., Toronto, Ontario, Canada
The Great Bear deposit lies within the Uchi Subprovince, ~25 km SE of Red Lake, Ontario. It is host to Au mineralization in polydeformed Archean volcanic and sedimentary rocks previously suggested to have reached greenschist to lower amphibolite facies conditions. The property is divided into a distinct northern felsic domain and southern mafic domain that are separated by a ~500m wide, NW-SE trending zone of strongly deformed rocks, referred to as the LP Fault Zone (LPFZ). This project focuses on constraining the metamorphic evolution across the property by: (1) determining the P-T conditions of observed mineral assemblage development; (2) determining if there are discernible metamorphic discontinuities across interpreted structures; (3) documenting and modelling metamorphic fluid production or infiltration; and (4) determining if the rocks experienced polymetamorphism.
Core logging and petrographic analysis of metamorphic mineral assemblages and reaction textures across the deposit allowed identification of the variability of metamorphic conditions, fluid production, and deformation fabrics. Metapelites with low variance metamorphic mineral assemblages in the felsic domain are concentrated within the zone of high strain along the LPFZ and are characterized by quartz + plagioclase + white mica + biotite ± garnet ± staurolite ± andalusite. Preliminary pseudosection modelling of mineral assemblage stability and plagioclase chemistry indicate that the rocks reached amphibolite facies peak metamorphism.
Metabasaltic rocks in the mafic domain have assemblages containing calcic and Fe-Mg amphibole + quartz + plagioclase ± chlorite ± biotite ± garnet ± carbonate. Metapelitic rocks south of the LPFZ and limb zone have assemblages of quartz + plagioclase + white mica ± biotite ± garnet ± staurolite ± andalusite. Mineral assemblages suggest that peak metamorphism is amphibolite facies and will be defined with phase equilibria modelling of individual samples, coupled with mineral chemistry of plagioclase and amphibole in the metabasaltic rocks. These results will be compared to the relatively well-constrained P-T conditions from the felsic domain to determine if there is a metamorphic discontinuity across the LPFZ.