Constraining the Formation and Alteration of Sudbury Breccia, Ontario, Canada: Implications for Footwall Cu-Ni-PGE Exploration
Abstract
Sudbury breccia is an impactite situated in the footwall of the 1.85 Ga Sudbury impact structure, situated in Ontario. Developing exploration vectors towards Sudbury breccia-hosted Cu-Ni-PGE mineralization is inhibited by an insufficient understanding of the relative contributions of footwall lithologies versus impact melt. By combining whole-rock geochemistry, field observations, statistical modelling and petrography, this study has determined that Sudbury breccia is a parautochthonous shock melt, which does not require a melt sheet contribution. Furthermore, the trace metal content of the breccia is largely controlled by the assimilation of mafic footwall lithologies, the exception being breccia proximal to mineralization, where a hydrothermally remobilized component is identified. Mineral chemistries demonstrate that some metal remobilization in breccia from both the North and South Range is associated with shear zones and hydrothermal-metamorphic activity. Biotites, amphiboles, chlorites and titanites have geochemical signatures consistent with increased pressure and/or temperatures conditions towards deformation structures hosting sulfide ores.