Convergent margin Ni-Cu-PGE-Cr ore systems: temporal and magmatic evolution

Ultramafic-mafic intrusions at convergent margins contain some of the world's significant Ni-Cu-PGE sulphide deposits and are becoming an increasingly important exploration target. This class of intrusions is well-represented in the accreted arc terranes of the northern Cordillera, particularly the Alaskan-type subclass. In this report, we describe current research on three Alaskan-type intrusions in British Columbia that are variably endowed in magmatic Ni-Cu-PGE mineralization. The goal of this project is to determine the timing of mineralization in relation to the temporal and magmatic evolution of the intrusion and to develop new mineral deposit models as guides for exploration. U-Pb and 40Ar/39Ar geochronological results for the Turnagain intrusion indicate multi-stage assembly of a composite body in the Early Jurassic (ca. 189-185 Ma) during initial accretion of arc terranes to the ancient North American continental margin. Ni(-Co) and Cu-PGE sulphide mineralization is partitioned within separate sub-intrusions that were emplaced during active accretion. A newly investigated zone of Cu-Pd-Pt sulphide mineralization in the Tulameen intrusion bears a strong resemblance to certain 'reef-style' deposits in layered intrusions. Preliminary geochronology results indicate emplacement of the Tulameen intrusive suite in the latest Triassic (ca. 204-206 Ma), coincident with the most prolific Cu-Au porphyry epoch in British Columbia. Investigation of magmatic sulphide occurrences at the Polaris Alaskan-type intrusion was initiated last summer and samples collected during the field season are currently being processed and examined.