Geological Evolution and Exploration Geochemistry of the Boomerang Lake Unconformity-type Uranium Prospect, Northwest Territories, Canada
Steve R. Beyer, Kurt Kyser, Eric E. Hiatt, Ian Fraser, 2010. "Geological Evolution and Exploration Geochemistry of the Boomerang Lake Unconformity-type Uranium Prospect, Northwest Territories, Canada", 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 Boomerang Lake unconformity-type uranium prospect is located in the Proterozoic western Thelon basin, Canada. Based on geological similarities to other uranium-producing Proterozoic basins, it represents a prospective target for uranium exploration. The potential of the western Thelon basin at Boomerang Lake to host high-grade, unconformity-type uranium deposits has been evaluated using alteration mineral paragenesis and chemistry, stable isotope geochemistry, 40Ar/39Ar geochronology, and a 2 percent HNO3 leach method.
Pre-Thelon basin basement rocks were subaerially weathered by low δ18O value meteoric waters at 1758 ± 7 Ma. Early diagenesis in the basin occurred at ca. 1667 Ma and is marked by a phosphate-dominated alteration mineral assemblage that formed from relatively reducing basinal fluids. Later peak diagenetic basinal fluids produced a widespread phyllosilicate-dominated mineral assemblage at temperatures of as much as 250°C, and had δ18O and δ2H values and chemical compositions consistent with those of oxidizing, saline basinal brines in other uranium-producing Proterozoic basins. Uranium mineralization is associated with hydrothermal alteration by 18O- and 2H-rich evolved basinal fluids at 200°C, but consists of minor amounts of the U+4 phosphate mineral tristramite. The distribution and stable isotope compositions of peak diagenetic and hydrothermal phyllosilicates indicate sandstones overlying the Boomerang Lake prospect were isolated from peak diagenetic basinal fluids that were capable of transporting uranium, resulting in the diminutive uranium phosphate mineralization.
Radiogenic mobile Pb is present in sandstones and basement rocks at Boomerang Lake, but was predominantly produced in situ from U-bearing accessory and detrital minerals and probably not from an undiscovered uranium deposit at depth. The use of 238U/206Pb and (Zr+Th)/U ratios proved to be helpful in evaluating the prospectivity of anomalously radiogenic zones in the Thelon basin.
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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.