METALLOGENY OF MAFIC-ULTRAMAFIC ROCKS AND ASSOCIATED NI-CU-PGE MINERALIZATION IN THE EAST ALASKA RANGE, ALASKA - A MAJOR TRIASSIC MAGMATIC CENTRE AND PLUMBING SYSTEM WITHIN WRANGELLIA

Triassic mafic-ultramafic intrusive complexes along the eastern margin of "Wrangellia” adjacent the Denali fault from northern British Columbia to east-central Alaska constitutes a newly recognized Ni-Cu-PGE metallogenic terrane that can be traced for at least 600 km (Hulbert, 1997). These sill-like intrusive centres acted as subvolcanic magma chambers that fed the extensive thick, overlying basalts and locally (Alaska) picritic pyroclastics of the Nikolai Group in an oceanic plateau flood basalt tectonomagmatic setting. Although the intrusive complexes in the Yukon portion of this metallogenic terrane have been the most productive (mined) and thoroughly documented to date, comparisons based on our recent studies in the East Alaska Range demonstrate that some of the striking differences, with respect to intrusion size, rock and mineral compostions, parental magma composition, nickel grades, deformation and metamorphism, and nature of the magmatic plumbing system and invaded countryrock stratigraphy, suggest that the Alaskan portion of this terrane has the more favourable attributes to produce a “World-Class” Ni-Cu-PGE mining camp. This talk will summarize 5 years of research on the metallogeny of mafic-ultramafic rocks and comagmatic Ni-Cu-PGE mineralization in the Mt Hayes, Quadrangle, East Alaska Range, Alaska, and its association with Triassic magmatism in Wrangellia. Detailed accounts of: the new geological map (1:50,000) of the area and its implications, volcanological studies, mineral and rock chemical investigations, platinum-group element surveys, isotopic and geochronological examinations, and geophysical imaging of this magmatic system will be presented. In addition, a new petrogenetic model will be presented to explain some of the lithological similarities and differences observed throughout Wrangellia, and the significance of ultramafic intrusions and Ni-Cu-PGE mineralization being confined to Eastern Wrangellia.