Sulphide Remobilization, Deformation and Durchbewegung: The BMK deposit, Saskatchewan, Canada

The Brabant Mckenzie (BMK) Cu, Zn, VMS deposit is hosted within a package of highly deformed and high grade metamorphosed bimodal volcanics, likely representing a backarc basin setting, inverted during the Trans Hudson Orogeny.  Mineralization comprises massive to semi massive sphalerite-pyrrhotite-pyrite and chalcopyrite contained within two major zones up to 18 m in width and part of a regional prospective trend.

VMS associated chlorite-sericite hydrothermal alteration protoliths are defined by coarse anthophyllite-cordierite-biotite-garnet assemblages in both the hangingwall and footwall of the sulphides. Detailed structural mapping and 3D modelling support a complex structural history with at least 5 deformation events (D₁ to D₅). Significant VMS remobilization, with durchbewegung texture, occurred during D₂, synchronous with peak metamorphism, anatexis, and the pervasive syn-migmatitic S₂ foliation. S₂ is folded by D₃, F₃ folds with a scatter of F₃ orientations suggesting either progressive D₂-D₃ noncylindrical ptygmatitc folds or subsequent refolding of F₃ axes. Mineral stretching lineations are locally developed and parallel the F₃ fold axes.  Late stage D₄ brittle ductile shears were synchronous with pegmatite emplacement. Pegmatites subparallel and transgress the dominant S₂ foliation and remobilized sulphides resulting in sphalerite, chalcopyrite and lesser gahnite spots, and locally coarse galena. Final D₅ brittle faulting is associated with minor offsets.