Archean Gold Mineralization in the Wabigoon Subprovince, a Product of Crustal Accretion: Evidence from U-Pb Geochronology in the Lake of the Woods Area, Superior Province, Canada

Abstract

Within the Lake of the Woods greenstone terrain, in the Wabigoon Subprovince of northwest Ontario, gold is in faults, shears, and tension veins that developed in response to a late Archean northwest-directed contraction and emplacement of contemporaneous plutons. Nine rocks in this area have been dated using U-Pb analyses of zircon in order to obtain precise time constraints on gold mineralization and to compare its timing with the age of major crustal events in the region. A mineralized dike at the Duport mine, Shoal Lake, is old, whereas a later dike that cuts mineralized rocks has an age of . Gold mineralization is therefore distinctly younger than calc-alkaline and tholeiitic rocks dated at in the Shoal Lake area and in the High Lake area to the north. Hydrothermal activity associated with mineralization at the Duport mine overprints the amphibolite-facies contact metamorphic aureole of the Snowshoe Bay batholith (). Gold is hosted by the Canoe Lake stock () and within structures adjacent to the stock that were formed during its emplacement, and it is part of a magmatic-hyrothermal alteration pattern surrounding, but not within, a late phase of the High Lake stock (). These data indicate that gold mineralization was closely linked in time to the emplacement of late intrusions and was likely a short-lived event that occurred at about 2709 Ma. It is contemporaneous with regional amphibolite-facies metamorphism in the Winnipeg River Subprovince to the north and with the earliest evidence for tectonic contact between the Wabigoon and Winnipeg River Subprovinces. Zircon from the Snowshoe Bay batholith shows inheritance from a source at least 2800 Ma in age. Rocks this old are unknown in the greenstone belt but are found in the adjacent Winnipeg River Subprovince, implying that sialic material derived from, or correlative with, the Winnipeg River Subprovince may have underlain greenstone units in the Shoal Lake area at 2709 Ma. These data, combined with other geochronological studies in the region, are compatible with collision of oceanic arc-derived volcanic rocks of the Wabigoon Subprovince with a continent or continental fragment now represented by the Winnipeg River Subprovince. Thrusting and imbrication of greenstone sequences over the edge of the sialic mass occurred at about 2709 Ma. Contemporaneous late magmatism and mobilization of auriferous fluids may have resulted from the interaction of slab and mantle-derived magmas with overridden sialic material.