Exploration for Komatiite-Associated Ni-Cu-(PGE) Mineralization in the Thompson Nickel Belt, Manitoba
D. Layton-Matthews, C. M. Lesher, O. M. Burnham, L. Hulbert, D. C. Peck, J. P. Golightly, R. R. Keays, 2010. "Exploration for Komatiite-Associated Ni-Cu-(PGE) Mineralization in the Thompson Nickel Belt, Manitoba", The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries, Richard J. Goldfarb, Erin E. Marsh, Thomas Monecke
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The Ni-Cu-(PGE) deposits of the Thompson nickel belt in the Circum-Superior boundary zone of northern Manitoba define the second largest Ni-Cu-(PGE) mining camp in Canada and one of the premiere Ni-Cu-(PGE) camps of the world. Despite a complex deformation and metamorphic history, the deposits in the Thompson nickel belt exhibit many fundamental characteristics similar to those of other major magmatic Ni-Cu-(PGE) districts: they are hosted by or associated with ultramafic intrusions that appear to represent dynamic feeders, the ores occur at or near the bases of the intrusions, and there is evidence for incorporation of significant amounts of sulfur from the Ospwagan Group metasedimentary country rocks. However, they differ from most other deposits of this type in being metamorphosed to much higher grades, in being much more complexly deformed, and in being mobilized to much greater degrees into the country rocks. The ultramafic intrusions are generally lensoid in shape, reflecting the effects of superimposed deformation on the enclosing metasedimentary rocks, range in composition from komatiitic dunite to komatiitic pyroxenite, are variably serpentinized, and are interpreted to represent a series of sills and low-angle dikes that intruded and interacted with the Ospwagan Group metasedimentary rocks. High Fo contents in relict igneous olivine (as much as Fo92) indicate a low Mg komatiitic parental magma with 22 to 24 percent MgO. Mineralization occurs as type II disseminated sulfides within the ultramafic rocks (e.g., William Lake), as type V tectonically modified massive sulfides within or adjacent to the ultramafic bodies (e.g., Pipe and Birchtree), and as type IV magmatically and metamorphically mobilized sulfides within metasedimentary rocks of the Ospwagan Formation (e.g., Thompson). Intrusions occur at all almost all levels within the Ospwagan Group, but mineralized intrusions are localized exclusively within the lower and middle parts of the Pipe Formation, which contains abundant sulfide-facies iron formation. Density-driven magma emplacement models indicate that the Ospwagan metasedimentary rocks were likely partially lithified prior to magma emplacement and the absence of significant thermal aureoles suggests that they were being metamorphosed. Stratigraphic correlations between ultramafic intrusions, S-rich rocks of the Pipe Formation, and Ni-Cu-(PGE) sulfide mineralization, together with nonmantle δ34S values and S/Se ratios in the ores and nonmantle Th/Yb and Th/Nb ratios in the host rocks, collectively suggest that the mineralization formed by incorporation of S-rich sedimentary rocks by high-temperature komatiitic magmas. Postore deformation and metamorphism have significantly modified the primary characteristics of many of the Thompson nickel belt ore deposits, mobilizing Cu, Au, and Pt. The best exploration tools appear to be aeromagnetic surveys to identify serpentinized ultramafic bodies, which are the heat and metal sources; stratigraphic studies to recognize appropriate levels of the Pipe Member of the Ospwagan Group, which is the S source; lithogeochemical studies to identify the most magnesian and most contaminated host units; which provide the evidence of magma-sediment interaction; and recognition of areas of anomalous Cu, Au, and Pt dispersion halos.
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The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries
VOLCANIC-ASSOCIATED and sedimentary-exhalative massive sulfide deposits on land account for more than one-half of the world's total past production and current reserves of zinc and lead, 7 percent of the copper, 18 percent of the silver, and a significant amount of gold and other by-product metals (Singer, 1995). A new source of these metals is now being considered for exploitation from deep-sea massive sulfide deposits. Because the oceans cover more than 70 percent of the Earth's surface, many expect the ocean floor to host a proportionately large number of these deposits. However, there have been few attempts to estimate the global mineral potential. Significant accumulations of metals from hydrothermal vents have been documented at some locations (e.g., 91.7 Mt of 2.06% Zn, 0.46% Cu, 58.5 g/t Co, 40.95 g/t Ag, and 0.51 g/t Au in the Atlantis II Deep of the Red Sea: Mustafa et al., 1984; Nawab, 1984; Guney et al., 1988). Even more metal is contained in deep-sea manganese nodules. Current estimates in the U.S. Geological Survey (USGS) mineral commodities summaries indicate a global resource of copper in deep-sea nodules of about 700 Mt. In the Pacific "high-grade" area, an estimated 34,000 Mt of nodules contain 7,500 Mt of Mn, 340 Mt of Ni, 265 Mt of Cu, and 78 Mt of Co (Morgan, 2000; Rona, 2003). A number of countries, including China, Japan, Korea, Russia, France, and Germany, are actively exploring this area.