Volcanic reconstruction of the paleoproterozoic powderhouse formation, Snow Lake, Manitoba, Canada: implications for controls on volcanogenic massive sulfide formation

Abstract

The Powderhouse formation of the Paleoproterozoic Snow Lake arc assemblage comprises the stratigraphic footwall to six volcanogenic massive sulfide deposits (VMS) at Snow Lake, Manitoba, Canada. It is interpreted to be a product of voluminous pyroclastic eruptions and concomitant subsidence followed by a period of relative volcanic quiescence that was dominated by suspension sedimentation, the reworking of these previously deposited pyroclastic units by debris flows and bottom currents, and localized emplacement of rhyolite domes. The rhyolite domes are spatially associated with the Chisel, Chisel North, Lost, Ghost, Photo and Lalor deposits. The Chisel, Lalor and Lost members comprise the Powderhouse formation and are subdivided into thirteen lithologically and chemically distinct lithofacies and allows, for the first time, correlation between the South Chisel basin and Lalor area. The Chisel and Lalor members contain lithofacies and bedforms that are characteristic of emplacement by subaqueous pyroclastic mass flows and concomitant subsidence. The Chisel member also contains coarse volcaniclastic breccias emplaced by mass debris flows derived from movement along fault scarps after early pyroclastic eruptions, and during continued subsidence. The Lost member consists of lithofacies deposited by mass flows generated from faults scraps during continued subsidence, but also contains lithofacies reworked by bottom currents and those deposited by suspension sedimentation, and locally coherent rhyolite. The Lost member represents a time stratigraphic interval, the “Ore Interval”, that marks contemporaneous rhyolite dome eruption, VMS formation, and a hiatus in explosive volcanism.