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Uvarova Y.A.,Queen's University | Kyser T.K.,Queen's University | Lahusen L.,Uravan Minerals Inc.
Journal of Geochemical Exploration | Year: 2012

The Paleoproterozoic Thelon Basin is located in the Churchill Province of the Canadian Shield, Nunavut, Canada, and is host to economic unconformity-type uranium mineralization (the Kiggavik deposit) and has the potential to host other deposits. The Thelon Formation sandstones and conglomerates and the Pitz Formation sandstones from the Garry Lake area contain phosphates, illite, minor chlorite and quartz as cements. The matrix phosphates are fluorapatite with U concentrations up to 103.5ppm in the Thelon Formation rocks and up to 991ppm in the Pitz Formation rocks. Lead isotope ratios and associated trace element concentrations extracted from sandstones and conglomerates by partial leaching with 2% nitric acid show that rocks with phosphates in the matrix have radiogenic 206Pb/ 204Pb ratios as well as high U, Pb, Th, Ca and P concentrations. Some radiogenic Pb is interpreted to be produced in situ by breakdown of fluorapatites. However, a 206Pb/ 204Pb vs. 238U/ 206Pb diagram indicates that in some samples there is an excess of 206Pb that could not have been produced by the amount of U in the sample and that must have been derived from an extraneous U-rich source and then introduced into the rock by later fluids. The Pb Pb model for leachates gives an age of ca. 1593Ma, which is younger than the age of the detrital and early diagenetic phosphates and is close to the age of the phosphate cements from the Garry Lake area of 1558Ma. This suggests that there was later remobilization and migration of uranium-bearing fluids when the aquifers were open to diagenetic fluids, which could have resulted in formation of a deposit in the north-eastern part of the Thelon Basin. © 2012.

Kyser K.,Queen's University | Lahusen L.,Uravan Minerals Inc. | Drever G.,Houston Lake Mining | Dunn C.,8756 Pender Park Drive | And 2 more authors.
Comptes Rendus - Geoscience | Year: 2015

The response in elemental concentrations and Pb isotopes in various surface media from the Cigar West unconformity-type uranium deposit located at a depth of 450m were measured to ascertain if element migration from the deposit can be detected at the surface. The media included clay-size fractions separated from the A2, B and C soil horizons, and tree cores and twigs from black spruce (Picea mariana) and jack pine (Pinus banksiana) trees. Lead isotopes were used to trace any effect on the surface media from the deposit at depth because the 207Pb/206Pb ratios in the ore are<0.1, whereas the background values in the basin are>0.7 and modern anthropogenic Pb from aerosols are near 0.9. The tree cores record their lowest and therefore most radiogenic 207Pb/206Pb ratios of<0.7 near the surface projection of the deposit and associated structures, particularly in tree rings that predate any exploration and drilling activity in the area. The median 207Pb/206Pb ratios increase in the order C, B soil horizon clays, tree cores, A2 soil clays and twigs because of the increasing contribution of common Pb with high ratios from anthropogenic sources that affect the shallowest media the most. Although this anthropogenic Pb as well as that from the background dominates the composition of all media at the surface and the contribution from the deposit at depth is diminished toward the surface, ore-related Pb is still present as a few percent of the composition of pathfinder elements and Pb isotopes. © 2015 Académie des sciences.

Beyer S.R.,Queen's University | Hiatt E.E.,University of Wisconsin - Oshkosh | Kyser K.,Queen's University | Dalrymple R.W.,Queen's University | Pettman C.,Uravan Minerals Inc.
Precambrian Research | Year: 2011

The Paleoproterozoic (Statherian) Thelon Formation consists of unmetamorphosed sandstone and conglomerate that was deposited in the Thelon Basin, a continental basin in northern Canada. This study presents the first detailed sedimentological and sequence stratigraphic analysis of the expansive and under-studied western Thelon Basin, and its relation to uranium mineralizing processes in the vicinity of the Boomerang Lake unconformity-related U prospect. Four lithofacies comprise the Thelon Formation in the western Thelon Basin, consisting of breccia, conglomerate, sandstone, and minor mudstone. These are grouped into four facies associations that represent deposition in alluvial fans and braided fluvial streams. Three stratigraphic sequences were identified based on the recognition of widespread surfaces that mark significant periods of subaerial exposure or changes in depositional environment. These unconformity-bounded sequences are composite in nature and can be subdivided into six high-frequency sequences (HFS). Low-accommodation and high-accommodation systems tracts are delineated, instead of the traditional systems tracts that are linked to changes in relative sea level, as no marine deposits are recognized in the Thelon Formation. Two significant strataform paleohydrogeological units were distinguished in the Thelon Formation, based on the relative timing of key diagenetic events such as compaction, grain dissolution, and cementation. Diagenetic aquicludes became isolated from basinal fluid flow due to stylolite-catalyzed early diagenetic quartz cementation, and occlusion of secondary intergranular macroporosity by kaolinite and muscovite, and minor dickite during later peak diagenesis. Diagenetic aquifers conducted U-bearing basinal fluids throughout diagenesis and are marked by an abundance of peak diagenetic dickite. Sequence stratigraphic correlation indicates that diagenetic aquicludes, which were not effective at conducting U-bearing basinal fluids, overlie the unconformity at the Boomerang Lake prospect and extend along the entire strike length of a related exploration trend. In contrast, thick diagenetic aquifers lie approximately 10. km to the north of the Boomerang Lake prospect along a different exploration trend. The western and eastern portions of the Thelon Basin experienced depositional environments and diagenetic conditions distinct from one another, suggesting that they were separate sub-basins. The western Thelon Basin contains fewer of the well-cemented facies that compartmentalized basinal fluid flow than the eastern Thelon Basin, and contains a kaolin-dominated diagenetic mineral assemblage rather than a muscovite-dominated assemblage that is common in the eastern Thelon Basin. In these regards, the western Thelon Basin evolved more similarly to the eastern portion of the Athabasca Basin, where thick, regional, kaolin-rich diagenetic aquifers were fluid conduits for the movement of the U-rich fluids that formed high-grade unconformity-related U deposits. © 2011 Elsevier B.V.

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