GEOCHEMICAL, ISOTOPIC, AND MINERALOGICAL CHARACTERIZATION OF THE FROBISHER SUITE MAFIC-ULTRAMAFIC SILLS, SOUTHERN BAFFIN ISLAND, CANADA, WITH IMPLICATIONS FOR METALLOGENIC POTENTIAL

The Frobisher Suite is a newly recognized magmatic province comprising mafic, ultramafic and layered mafic-ultramafic sills in southern Baffin Island, Nunavut. The sills are emplaced into the metasedimentary strata of the middle Paleoproterozoic Lake Harbour Group, where they vary in thickness from several meters to hundreds of meters and extend for several kilometers along strike. During closure of the Manikewan Ocean and resulting evolution of the collisional Trans-Hudson orogen, the sills were subjected to several deformation and metamorphic events, including metamorphism to granulite facies conditions. Sills vary from well-layered to massive, and exhibit homogeneous to heterogeneous mineral grain distribution. The majority of the mafic units contain the assemblage plagioclase + hornblende + orthopyroxene + clinopyroxene, with a lesser number containing the assemblage plagioclase + hornblende. Ultramafic units mostly contain the assemblage hornblende + olivine + clinopyroxene ± spinel, with a subset containing hornblende + olivine ± spinel. Based on major and trace element chemistry, the Frobisher Suite can be divided into eight geochemical groups. The major geochemical components potentially indicate that melting occurred to differing degrees within a mantle plume head, at various depths below the Meta Incognita microcontinent at ca. 1900 Ma. Some sills appear to have been emplaced as multiple injections of either single or multiple magma types, with some displaying evidence for fractionation prior to sill formation. Disseminated sulphides are present in the sills, and in some cases, in the adjacent host psammite. Based on a preliminary assessment, it appears that the tholeiitic low-Ti groups serve as the best targets for Ni-Cu-PGE exploration, and have the greatest potential to host high-tenor magmatic sulphide mineralization. At this stage, the Frobisher Suite may be considered to define its own large igneous province (LIP), termed the “Frobisher LIP”.