Evolulion of the Paleoprotemzoic Snow Lake arc assemblage and geodynamic setting for associated volcanic- hosted massive sulphide deposits, Flin Flon Belt, Manitoba, Canada

摘要

The majority of volcanogenic massive sulphide(VMS) deposits at the east end of the Paleoproterozoic Flin Flon"greenstone" belt occur in the 1.89 Ga Snow Lake arcassemblage. VMS deposits in this isotopically juvenile oceanicarc sequence are hosted within a 6 km thick monoclinal sectionthat records in its stratigraphy and geochemistry a temporalevolution in arc development from primitive, through mature, toarc rift. VMS deposits occur in both the primitive and maturearc sequences and are interpreted to be products of arc extensionand accompanying anomolously high heat flow, fracturing, andfluid circulation. Boninites, low-Ti tholeiites, and isotopicallyjuvenile rhyolite flows, a rock association that has beenattributed in both modern and Phanerozoic arcs to high-temperature hydrous melting of refractory mantle sources in anextensional and (or) proto-arc environment, forms the primitivearc. Indication that the mature arc also underwent extensionincludes voluminous volcaniclastic detritus (from fault scarps?),prominent synvolcanic dykes, isotopically juvenile rhyoliteflows, and the fact that the mature arc is stratigraphicallyoverlain by arc-rift basalts with MORB-like geochemistry.Interpretation of VMS deposits at Snow Lake as products of anextensional geodynamic setting suggests that the traditional FlinFlon Belt exploration model, invoking "pluton-generated"convective seawater, be augmented by the search for evidence ofrifting. Economically significant rock associations at Snow Lakeinclude geochemically primitive refractory mafic magmas (e.g.,boninites), isotopically juvenile felsic magmas, bimodal basalt-rhyolite sequences, and arc-rift basalts.