Geochemistry of the 130 to 80 Ma Canadian High Arctic Large Igneous Province (HALIP) Event and Implications for Ni-Cu-PGE Prospectivity

摘要

The geochemistry of a suite of lava flows, sills, and dikes from Axel Heiberg and Ellesmere islands in Arctic Canada has been examined to determine the Ni-Cu-platinum group element (PGE) sulfide prospectivity of the Canadian portion of the 130 to 80 Ma High Arctic large igneous province (HALIP). This event can be split into mildly alkaline or transitional and tholeiitic suites, each with distinct provenances, S saturation histories, and Ni-Cu-PGE prospectivity. The mildly alkaline magmas of the HALIP were sourced from a deep, variably enriched part of the mantle, and most probably represent lower-degree partial melts than the tholeiitic parts of the HALIP that were formed from magmas generated by shallower, higher-degree partial melting of a region of unenriched mantle. The two types of magma also differ in their Ni-Cu-PGE magmatic sulfide prospectivity, in that the geochemistry of the majority of the mildly alkaline samples is indicative of unfertile or poorly fertile S-saturated magmas which did not sequester significant amounts of chalcophile elements from the mantle during partial melting, and therefore may be unprospective. In comparison, the presence of chalcophile element-undepleted tholeiitic samples suggests that the magmas forming these rocks were S undersaturated and fertile, and sequestered significant amounts of Cu and PGEs from the mantle during partial melting. Furthermore, the presence of chalcophile-depleted and crustally contaminated samples within the tholeiitic suite indicates that the magmas that formed these samples assimilated crustal material and became sulfur saturated prior to emplacement, segregating magmatic sulfides that may have been deposited and left behind within ultramafic or mafic intrusive rocks associated with the tholeiitic segments of the Canadian HALIP. Interestingly, some tholeiitic flows are crustally contaminated but are only weakly Pd depleted; this suggests that these flows may have locally assimilated crustal material, which led to only minor S saturation and in situ formation of voluminously insignificant magmatic sulfides.These observations suggest that the tholeiitic portion of the Canadian HALIP is prospective for Ni-Cu-PGE sulfide mineralization, and that mafic-ultramafic sequences associated with this suite should be targeted for mineral exploration. Identification of parts of the Canadian HALIP where magmas assimilated S-bearing sedimentary material could also be a useful tool for exploration. The data and interpretations presented here provide a number of scientific hypotheses that could be tested for other parts of the circum-Arctic HALIP event.