The Bird River sill (BRS) is composed of layered mafic-ultramafic intrusive bodies which intruded the Bird River greenstone belt in southeastern Manitoba. Layered intrusions, such as those that collectively make-up the BRS, are important hosts to base and precious metal deposits. This study was initiated to examine and develop an emplacement model for the western half of the BRS and to establish the controls on Cr-Ni-Cu-PGE mineralization. The BRS intrusions were emplaced through multiple-magmatic injections into different stratigraphic levels in the Lamprey Falls Formation. It is interpreted that the central BRS intrusions are connected and represent a single conduit system. The BRS and the Lamprey Falls Formation are overlain by the metasedimentary rocks of the Peterson Creek Formation and are overturned. The stratigraphy of the BRS is divided into four series which are from the base upwards: 1) marginal mafic series, 2) ultramafic series, 3) transition series, and 4) mafic series. All significant concentrations of Cr-Ni-Cu-PGE are contained in the ultramafic series. Mineralization is magmatic in origin with significant Ni-Cu and PGE remobilization associated with late felsic magmatism. Ni-Cu remobilization is also associated with mineralized shear zones that cross-cut the BRS and Lamprey Falls Formation. The sulphur source could not be determined unambiguously based on sulphur isotopes alone but the δ34S values of the BRS intrusions suggests that the sulphur in the BRS is magmatic in origin and that two of the BRS bodies may have assimilated external sulphur. The findings of this investigation have considerable economic implications. The model that each BRS body is an individual intrusion implies each body may contain its own style of mineralization. Secondly, the Page body of the BRS is interpreted to represent a turbulent magmatic environment and to be the first intrusion to form at the lowest stratigraphic level. The magmas that formed the stratigraphically higher BRS intrusions are believed to have passed through the Page intrusion. Therefore, the Page body is an excellent exploration target as it represents a turbulent environment in which significant amounts of primitive magma have passed through which are two key factors in the formation of Ni-Cu-PGE deposits.

The Bird River sill (BRS) is composed of layered mafic-ultramafic intrusive bodies which intruded the Bird River greenstone belt in southeastern Manitoba. Layered intrusions, such as those that collectively make-up the BRS, are important hosts to base and precious metal deposits. This study was initiated to examine and develop an emplacement model for the western half of the BRS and to establish the controls on Cr-Ni-Cu-PGE mineralization. The BRS intrusions were emplaced through multiple-magmatic injections into different stratigraphic levels in the Lamprey Falls Formation. It is interpreted that the central BRS intrusions are connected and represent a single conduit system. The BRS and the Lamprey Falls Formation are overlain by the metasedimentary rocks of the Peterson Creek Formation and are overturned. The stratigraphy of the BRS is divided into four series which are from the base upwards: 1) marginal mafic series, 2) ultramafic series, 3) transition series, and 4) mafic series. All significant concentrations of Cr-Ni-Cu-PGE are contained in the ultramafic series. Mineralization is magmatic in origin with significant Ni-Cu and PGE remobilization associated with late felsic magmatism. Ni-Cu remobilization is also associated with mineralized shear zones that cross-cut the BRS and Lamprey Falls Formation. The sulphur source could not be determined unambiguously based on sulphur isotopes alone but the δ34S values of the BRS intrusions suggests that the sulphur in the BRS is magmatic in origin and that two of the BRS bodies may have assimilated external sulphur. The findings of this investigation have considerable economic implications. The model that each BRS body is an individual intrusion implies each body may contain its own style of mineralization. Secondly, the Page body of the BRS is interpreted to represent a turbulent magmatic environment and to be the first intrusion to form at the lowest stratigraphic level. The magmas that formed the stratigraphically higher BRS intrusions are believed to have passed through the Page intrusion. Therefore, the Page body is an excellent exploration target as it represents a turbulent environment in which significant amounts of primitive magma have passed through which are two key factors in the formation of Ni-Cu-PGE deposits.

The Bernic Lake Formation in the Bird River greenstone belt consists dominantly of mafic to felsic arc volcanic and volcaniclastic rocks, with varying amounts of mafic to felsic intrusive rocks, including the Bernic Lake pegmatite group. U-Pb geochronoligical analyses on selected samples around the Bernic Lake area, indicate that the Tanco gabbro, the Birse Lake granodiorite and the volcanic rocks of the Bernic Lake Formation are contemporaneous ca. 2724 Ma and form part of a singular volcanic and subvolcanic complex. The highly evolved, LCT-type, rare element-bearing Bernic Lake pegmatite group, including the world class Tanco pegmatite, was emplaced in the Bernic Lake Formation during a belt-scale tectonomagmatic event associated with G3 deformation between ca. 2650 and 2640 Ma. Early and rarely preserved isoclinal folding in the Bernic Lake Formation attributed to G1 deformation was followed north-south directed compression resulting in refolding and transposition of G1 structures by east-west trending upright F2 folds. Continued compression caused strain localization and south-side-up shearing along the North Bernic Lake Shear Zone (NBLSZ), which juxtaposes MORB-like basalt of the south panel to the south against arc rocks of the Bernic Lake Formation to the north. G3 deformation is characterized by a spaced S3 fracture cleavage that overprints the penetrative S2 fabric, and dextral reactivation of the NBLSZ. Pegmatitic melt ascended from depth along the reactivated NBLSZ during this time and was emplaced both within the shear zone and within rock units adjacent to it. The shapes and orientations of the pegmatites are controlled in part by the rheology of the host rocks into which they were emplaced. Rheologically competent lithologies responded to G3 strain by brittle fracture and the pegmatites occurring therein are flat and tabular; rheologically incompetent lithologies responded to G3 strain by ductile-brittle deformation and the pegmatites therein are irregular, folded, and/or boudinaged. The contrasting styles suggest that the pegmatites intruded while the rocks of the Bernic Lake Formation were at or near the brittle-ductile transition.

The Bernic Lake Formation in the Bird River greenstone belt consists dominantly of mafic to felsic arc volcanic and volcaniclastic rocks, with varying amounts of mafic to felsic intrusive rocks, including the Bernic Lake pegmatite group. U-Pb geochronoligical analyses on selected samples around the Bernic Lake area, indicate that the Tanco gabbro, the Birse Lake granodiorite and the volcanic rocks of the Bernic Lake Formation are contemporaneous ca. 2724 Ma and form part of a singular volcanic and subvolcanic complex. The highly evolved, LCT-type, rare element-bearing Bernic Lake pegmatite group, including the world class Tanco pegmatite, was emplaced in the Bernic Lake Formation during a belt-scale tectonomagmatic event associated with G3 deformation between ca. 2650 and 2640 Ma. Early and rarely preserved isoclinal folding in the Bernic Lake Formation attributed to G1 deformation was followed north-south directed compression resulting in refolding and transposition of G1 structures by east-west trending upright F2 folds. Continued compression caused strain localization and south-side-up shearing along the North Bernic Lake Shear Zone (NBLSZ), which juxtaposes MORB-like basalt of the south panel to the south against arc rocks of the Bernic Lake Formation to the north. G3 deformation is characterized by a spaced S3 fracture cleavage that overprints the penetrative S2 fabric, and dextral reactivation of the NBLSZ. Pegmatitic melt ascended from depth along the reactivated NBLSZ during this time and was emplaced both within the shear zone and within rock units adjacent to it. The shapes and orientations of the pegmatites are controlled in part by the rheology of the host rocks into which they were emplaced. Rheologically competent lithologies responded to G3 strain by brittle fracture and the pegmatites occurring therein are flat and tabular; rheologically incompetent lithologies responded to G3 strain by ductile-brittle deformation and the pegmatites therein are irregular, folded, and/or boudinaged. The contrasting styles suggest that the pegmatites intruded while the rocks of the Bernic Lake Formation were at or near the brittle-ductile transition.