Ni-Cu-PGE mineralization of the 1.1 Ga Midcontinent Rift of N. America: rethinking models for the rift and the implications for mineralization

摘要

The ~1.1 Ga Midcontinent Rift (MCR) of North America comprises ~1,500,000 km3 of basaltic sheets, flows and intrusive rocks emplaced in the Lake Superior region during the Mesoproterozoic (Klewin and Shirey 1992). Recent discoveries of high-grade Ni-Cu-PGE deposits within mafic intrusions associated of the MCR has resulted in a significant increase in exploration activity in the Lake Superior region. Many of these deposits, particularly Thunder North in Ontario, Tamarack in Minnesota, and Eagle in Michigan, are associated with ultramafic intrusions emplaced during an early phase of rift activity and are often spatially linked with long-lived crustal structures (Hollings et al. 2007). The Thunder Bay - Lake Nipigon region is emerging as the most prospective PGM-rich mag-matic sulfide district in Canada and, arguably, the world. It has delivered the highest number of new platinum group metal discoveries over the past 15 years.