Magmatic and Metamorphic Uraninite Mineralization in the Western Margin of the Trans-Hudson Orogen (Saskatchewan, Canada): A Uranium Source for Unconformity-Related Uranium Deposits?

Abstract

The genetic model for the giant unconformity-related uranium deposits of the Athabasca Basin is still being debated, with one of the main issues being the source of the uranium concentrated by Mesoproterozoic era (ca. 1.60-1.00 Ga) diagenetic-hydrothermal events at the interface between the Athabasca Basin and the underlying Archean/Paleoproterozoic basement rocks. Currently, accessory minerals like monazite, zircon, and/or apatite from the sedimentary basin and basement rocks are proposed as the primary uranium source for these high-grade uranium deposits. Numerous occurrences of U mineralization of Hudsonian age have been documented for decades all around the Athabasca Basin; however, so far these have not been regarded as viable U sources. Here, a systematic and detailed study of two areas of basement rocks near the eastern part of the Athabasca Basin is presented (i.e., the Way Lake property, lying outside the current margin of the basin, and the Moore Lakes property, currently covered by the basin). This study highlights the significant and widespread occurrence of Hudsonian (ca. 1.81-1.76 Ga) uranium oxide (UO2) mineralization in these zones. Two types of mineralization are identified and documented here: magmatic uranium oxides related to granitic pegmatites and leucogranites, which are more common, and high-temperature, vein-hosted uranium oxides, which have the highest grades. The two types were formed during the peak (1.82-1.81 Ga) and/or postthermal peak (1.81-1.72 Ga) events related to the evolution of the Trans-Hudson orogeny. The magmatic uranium oxides formed by partial melting of Wollaston Group metasedimentary rocks. The origin of the vein-type occurrences is unclear, but their high thorium and rare earth element (REE) contents suggest a high-temperature process associated with Ca and/or Na metasomatism. The uranium oxides are associated with other U-, Th-, and REEbearing accessory minerals like U-rich thorite, thorite, zircon, and/or monazite, adding to the exceptional U contents (100-2,460 ppm) of these UO2-bearing rocks (up to 200 times more primarily enriched in U than other basement or basin rock types). A 3-D model of a 1,300 × 630 × 200-m basement zone from the Way Lake property indicates that uraninite-bearing granitic pegmatites and leucogranites represent 7% of the total volume of crystalline rock. Within this rock volume are approximately 8,121 (assuming a mean U content of 250 ppm) to 16,242 (assuming a mean U content of 500 ppm) tonnes U. The U tonnage of this limited rock volume, contained mainly by the Hudsonian-age UO2, corresponds to between 4% (for McArthur River) and 103% (for Rabbit Lake) of the U tonnage of known unconformity-related U deposits of the basin.Some of the studied rock samples, even macroscopically fresh and located far away from any known unconformity-related U deposit, present clear evidence of alteration, including clay minerals, aluminophosphatesulfate (APS) minerals, and UO2 dissolution, indicating the percolation of the brines associated with the formation ...

Geochronology of Hydrothermal Processes Leading to the Formation of the Au–U Mineralization at the Rompas Prospect, Peräpohja Belt, Northern Finland: Application of Paired U–Pb Dating of Uraninite and Re–Os Dating of Molybdenite to the Identification of Multiple Hydrothermal Events in a Metamorphic Terrane

“…The most comprehensive geochronolgical studies on uraninite-bearing ore deposits have been completed in the Athabasca Basin and adjacent areas in Canada [1,4,45,46], as well as in the McArthur and Mt. Isa basins in Australia [3,[47][48][49].…”

Tectono-metamorphic evolution of the pre-Athabasca basement within the Wollaston–Mudjatik Transition Zone, Saskatchewan

“…These rocks were affected by a complex, polyphased deformation, high-grade metamorphism and associated partial melting, and emplacement of plutonic rocks during the final stage of the THO and the latecollisional event at 1.83-1.76 Ga Chiarenzelli et al 1998;Annesley et al 2001Annesley et al , 2005Mercadier et al 2013). Pressure-temperature (P-T) conditions associated with the peak metamorphism of the Hudsonian orogeny, between 1.83 and 1.80 Ga, have been estimated at about 800°C and 8 kbar (1 kbar = 100 MPa) (Annesley et al 2005).…”

“…The higher uranium fertility of the upper levels of the crust (at ϳ4-5 kbar) is reinforced by the development at a crustal scale of steep S2/C2 and C2= shear zones that favor melt segregation and transfer of melt towards upper levels where they could differentiate and crystallize as uraniumenriched pegmatites. Mercadier et al (2013) have dated uranium oxides in pegmatites within the WMTZ at ca. 1.81 and 1.76 Ga, indicating uranium-enriched pegmatite formation during peakand post-thermal evolution, respectively.…”

Integration of geophysical and geological data for delimitation of mineralized zones in Um Naggat area, Central Eastern Desert, Egypt

“…This allowed the migration of very low soluble elements (Th, Zr and REE) together with U. They may derive a part or all of their enrichment from such processes and not only from partial melting of an U-Th-REE-rich protolith as is usually proposed (Cuney and Kyser, 2008;Mercadier et al, 2013).…”