Magmatic Ni-Cu-PGE sulphide deposits at convergent margins

Magmatic Ni-Cu-PGE sulphide deposits hosted by ultramafic-mafic intrusions in convergent-margin tectonic settings are an increasingly important resource worldwide, yet remain poorly understood and underexplored. A compilation of global mineralized intrusions in subduction-related settings underscores their economic potential and reveals mineralogical differences that may reflect parental magma composition and ore-forming processes. Our geochemical and isotopic investigations of two mineralized ultramafic intrusions in the Cordillera, the orthopyroxene-absent Turnagain Alaskan-type intrusion and the orthopyroxenerich Giant Mascot intrusion, emphasize (1) the importance of wall-rock assimilation in promoting sulphide saturation and formation of an immiscible sulphide liquid; and (2) the ability of narrow conduit systems to channel influxes of new metal-laden magma and serve as traps for the collection of upgraded Ni-Cu-PGE sulphides. Processes fundamental to the production of economic Ni-sulphide deposits in the oxidized and hydrous primitive magmas generated at subduction zones are similar to those that have produced worldclass magmatic nickel deposits in other tectonic settings.