Structural study of Sudbury breccia and sulphide veins, Levack embayment, North Range of the Sudbury structure, Ontario

The ca. 2.7 Ga Levack gneiss complex underlies the Levack embayment and northern part of the Sudbury structure. Sudbury breccia, a unit of centimetre- to metre-scale clasts and blocks in a fine-grained to aphanitic matrix, occurs as veinlets, veins, and irregular, disconnected, metre-wide massive bodies within wide breccia zones that cut the Levack gneiss complex. Sudbury breccia veins show no systematic orientations or displacements. Conjugate sets of chalcopyrite veins hosted by Sudbury breccia, and veins filled by hydrothermal minerals at the Barnet showing, were emplaced in tensile fractures perpendicular to the gneissic foliation. Observations suggest that the Sudbury breccia originated by in situ brecciation during propagation of impact shock waves, rather than by milling and friction melting along superfaults during collapse of impact crater walls. Sulphide veins were emplaced in tensile fractures that propagated perpendicular to gneissic foliation and coincided with hydrothermal activity.