This review of the geology, geophysics, and origin of the unconformity-associated uranium deposit type is focused on the Athabasca Basin. Pods, veins, and semimassive replacements of uraninite (var. pitchblende) are located close to unconformities between late Paleo-to Mesoproterozoic conglomeratic sandstone basins and metamorphosed basement rocks. The thin, overall flat-lying, and apparently unmetamorphosed but pervasively altered, mainly fluvial strata include red to pale tan quartzose conglomerate, sandstone, and mudstone. Beneath the basal unconformity, red hematitic and bleached clay-altered regolith grades down through chloritic altered to fresh basement gneiss. The highly metamorphosed interleaved Archean to Paleoproterozoic granitoid and supracrustal basement gneiss includes graphitic metapelitic that preferentially hosts reactivated shear zones and many deposits. A broad variety of deposit shapes, sizes and compositions ranges from monometallic and generally basement-hosted veins to polymetallic lenses located just above or straddling the unconformity, with variable Ni, Co, As, Pb and traces of Au, Pt, Cu, REEs, and Fe. Résumé Cet examen de la géologie, de la géophysique et de l'origine des gîtes d'uranium associés à des discordances est focalisé sur le bassin d'Athabasca. Les minéralisations d'uraninite (variété pechblende) qui prennent la forme de lentilles, de filons ou de corps semi-massifs de remplacement se situent près de la discordance entre des grès conglomératiques de bassin du Paléoprotérozoïque tardif au Mésoprotérozoïque et les roches du socle métamorphisées. La succession sédimentaire de bassin est mince, repose dans l'ensemble à plat, est apparemment non métamorphisée, mais profondément altérée, et se compose principalement d'unités fluviatiles constituées de conglomérats quartzeux, de grès et de mudstones de couleur rouge à chamois pâle. Sous la discordance marquant la base de la succession sédimentaire, un régolite hématitique rouge, décoloré par endroits par une altération argileuse, passe progressivement vers les profondeurs du socle à des gneiss chloritisés puis à des gneiss non altérés. Les roches très métamorphisées du socle, formées d'une intercalation de gneiss granitoïdes et de gneiss supracrustaux de l'Archéen au Paléoprotérozoïque, incluent des métapélites graphitiques qui renferment de manière préférentielle des zones de cisaillement réactivées et un grand nombre de gîtes. Les gîtes sont de formes, de dimensions et de compositions très variées, passant de minéralisations monométalliques, généralement sous forme de filons encaissés dans le socle, à des lentilles polymétalliques présentant des concentrations variables de Ni, Co, As, Pb et des traces de Au, Pt, Cu, de terres rares et de Fe, qui se situent à cheval sur la discordance ou à peu de distance au-dessus. Definition Unconformity-associated uranium deposits are pods, veins, and semimassive replacements consisting of mainly uraninite dated mostly 1600 to 1350 Ma, and located close to basal unconformities between Proterozoi...
Stratigraphic evidence suggests sporadic rifting began during deposition of the mainly platformal Mackenzie Mountains Supergroup: minor magnetite iron-formation in shale basins, lead–zinc in karsted and brecciated carbonates, red-bed and evaporite wedges, and basalts at the top. In the unconformably overlying Coates Lake Group similar climates and definite rifting are recorded by thin orthoconglomerates with thick red-bed and evaporite wedges containing stratiform copper deposits in paleovalleys. Unconformably above this, basal Windermere Supergroup records major climatic change and more emphatic rifting, with thick orthoconglomerates next to fault scarps overlain by glaciomarine deposits with volcanics and hydrothermal iron-formation.A quartz diorite plug, here dated by the U–Pb zircon method at [Formula: see text], is bounded by faults but is contained in a thrust panel together with Mackenzie Mountains Supergroup and is chemically similar to diabase sills previously dated at 766–769 ± 27 Ma (Rb–Sr). A diatreme intruding Coates Lake Group contains clasts of granite and gneiss from inferred basement. U–Pb systematics from a granite clast indicate inherited zircons about 1.6 ± 0.25 Ga in age and crystallization between 1100 and 1175 Ma, a maximum age for Mackenzie Mountains Supergroup.
Elevation of the Shaler Group to supergroup status and the following internal revisions are proposed in order to more properly reflect rock units of the Amundsen Basin. The names Escape Rapids, Mikkelsen Islands, Nelson Head and Aok are proposed to replace the lower clastic, cherty carbonate, upper clastic, and orange-weathering stromatolite members of the Glenelg Formation in Minto and Cape Lambton inliers, informal map units 19 to 21, 22, 23, and 24 in the Coppermine area and informal map units P1, P2, P3, and P4a in Brock Inlier, respectively. Collectively these are to be known as the Rae Group; the name Glenelg Formation is abandoned. The former Reynolds Point Formation is raised to group status and comprises the Grassy Bay, Boot Inlet, Fort Collinson and Jago Bay formations, which replace the lower clastic, lower carbonate, upper clastic and upper carbonate members in Minto Inlier and informal map units P4b, P4c, lower P4d and upper P4d in Brock Inlier, respectively.
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