COMPARING THE VOLCANOLOGY AND GEOCHEMISTRY OF NEOARCHEAN VMS-ENDOWED AND VMS-DEPRIVED GREENSTONE BELTS IN THE WAWA SUBPROVINCE OF THE SUPERIOR CRATON

The Wawa subprovince of the Superior craton experienced significant, widespread volcanism and greenstone belt construction, circa 2720 Ma, along its northern margin before colliding with and subducting under the Quetico and Wabigoon subprovinces around 2695-2680 Ma. These greenstone belts along the northern margin of the Wawa subprovince were interpreted to have formed within similar tectonic environments and to have experienced similar styles of volcanism, yet they have vastly different endowments of volcanogenic massive sulphide (VMS) deposits. The 2720 Ma greenstone belts examined in this study are the VMS-endowed Manitouwadge and Winston Lake greenstone belts, and the VMS-deprived Shebandowan and Vermilion greenstone belts.

VMS deposits [Cu-Zn-Pb±Au±Ag] form in extensional submarine geodynamic environments where they are a product of synvolcanic, high-temperature hydrothermal systems. Despite relatively continuous mineral exploration in the Shebandowan belt, very little bonafide VMS mineralization has been recognized and no deposits have been discovered. The Vermilion greenstone has received less exploration and appears to have prospective strata yet no economic deposits have been discovered to date. The lack of VMS mineralization in these belts is in marked contrast to the substantially smaller, time and stratigraphically equivalent Manitouwadge and Winston Lake greenstone belts that host the Geco (~50 Mt), Willroy (~4.5 Mt) and Winston Lake (~3.1 Mt) VMS deposits.

This disparity in VMS deposit endowment will be examined through a comparison of the volcanic, tectonic and petrogenetic history of the VMS-endowed and VMS-deprived belts. Regional- and property-scale mapping and sampling through the volcanic strata in each greenstone belt have been completed to test several factors limiting the formation VMS deposits in the Shebandowan and Vermilion greenstone belts. These factors include the role of water depth during volcanism (i.e. boiling hydrothermal systems), the role of juvenile arc volcanism versus interaction with older basement, and/or variations in the tectonic setting/conditions during volcanism.