Geochemistry and mineralizaton of the Lundmark Akow area, North Caribou Greenstone belt, Ontario

Abstract

The Lundmark Akow area is located in the south-central porƟon of the South Rim assemblage of the North Caribou Greenstone Belt. The mineralizaƟon consists of several base metal-bearing massive sulphide horizons hosted in a sequence of garneƟferous staurolite mica schists in the southern porƟon of the study area, to a northern host rock sequence dominated by volcanic and intrusive mafic to felsic rocks. The igneous host rock porƟon of the study has been dated between 2973 to 2980 Ma through zircon U/Pb geochronology. The meta-sedimentary sequence which hosts the mineralizaƟon is built upon a basement of intrusive and volcanic rocks which formed in an oceanic plateau through plume magmaƟsm before impinging upon a subducƟon zone. NegaƟve high field strength element (HFSE) anomalies show that arc related magmaƟsm built upon the oceanic plateau. Sm/Nd isotope values from the mafic to felsic volcanic and intrusive rocks show a spread in εNd from -1.53 to 3.07 suggesƟng that melts were derived from both depleted mantle and plume sources, with some melts being contaminated by an older crustal basement. The characterisƟcs of the massive sulphide horizons, as well as the host meta-sedimentary rocks are consistent with them having formed through distal VMS processes including hydrothermal parƟculate fallout from buoyant plumes combined with pooling of dense sulphide-rich fluids in topographic lows on the sea floor. The garnet-rich meta-sedimentary rocks show Fe and Mn enrichment when normalized to immobile Al and Ti, consistent with addiƟon through hydrothermal plume parƟculate processes. The characterisƟcs of the garnet layers suggest they formed through metamorphism of a sediment derived from the intermixing of hydrothermal and terrigenous parƟculates. The garnet composiƟons show prograde growth with a Mn- and Ca-rich core to a Fe- and Mg-rich rim, supporƟng their formaƟon as a result of metamorphic condiƟons post exhalaƟve acƟvity. [...]