Paleoproterozoic gold and its tectonic triggers and traps: implications from Re-Os sulphide and U-Pb detrital zircon geochronology, Lynn Lake, Manitoba

Abstract

Orogenic Au deposits require a trigger to transport auriferous fluids from their deep-seated source regions to their depositional site in the mid- to upper-crust. Defining the tectonic trigger of Au ore systems requires precise age constraints. Herein we address that knowledge gap with new Re-Os sulphide (arsenopyrite and pyrite) and U-Pb detrital zircon geochronology results from the Lynn Lake greenstone belt of the Paleoproterozoic Trans-Hudson Orogen, Manitoba, Canada. We document an early-stage of Au-rich veins (ca. 1.82 Ga) that are coeval with syenitic magmatism (1.83-1.82 Ga) and immediately post-date new ages for the opening and closure of synorogenic basins (1.84-1.83 Ga) and late-stage arc magmatism (1.84-1.83 Ga). Together these data point to the importance of stalled subduction and upwelling asthenosphere as possible triggers for fluid release during the earliest stages of continental collision between the Hearne, Superior, and Sask cratons. New dating further documents a second, overprinting generation of auriferous fluids (ca. 1.78 Ga) that post-dates peak metamorphism (ca. 1.81 Ga). These late-stage fluids were driven by a second thermal pulse (ca. 1.78 Ga), which, based on the timing of coeval, crustally derived pegmatitic dykes, may be related to crustal thickening and/or another unrecognized subcrustal heat source. Mineral exploration should focus on the large-scale architecture that is required to focus multiple pulses of auriferous fluids to the same depositional trap over the lifespan of an orogen.