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TitleIntegrated geodatabase study of the complexly deformed U-hosting Paleoproterozoic Amer Group, Nunavut
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorCalhoun, L; White, J C; Jefferson, C W; Patterson, J; Tschirhart, VORCID logo
SourceGeological Survey of Canada, Scientific Presentation 19, 2014, 26 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Mediaon-line; digital
RelatedThis publication is related to Integrated geodatabase study of the complexly-deformed U-hosting Paleoproterozoic Amer Group, Nunavut
File formatppt; pdf
NTS66H/06; 66H/07; 66H/08; 66H/09; 66H/10; 66H/11
Lat/Long WENS-97.1167 -96.2833 65.6167 65.4167
Subjectsradioactive minerals; stratigraphy; structural geology; geophysics; stratigraphic analyses; stratigraphic correlations; structural features; structural interpretations; structural analyses; geophysical surveys; aeromagnetic surveys; aeromagnetic interpretation; uranium; granites; faults; syenites; lithostratigraphy; Archean; Amer Group; Thelon Basin; Amer Belt; Kethet River Group; Oora Lake Formation; Showing Lake Formation; Itza Lake Formation; Three Lakes Formation; Five Mile Lake Formation; Aluminum River Formation; Resort Lake Formation; Ayagaq Lake Formation; Proterozoic; Precambrian
Illustrationsstratigraphic columns; photographs; location maps; block diagrams
ProgramGEM: Geo-mapping for Energy and Minerals Uranium
Released2014 01 23
The uranium-hosting Paleoproterozoic Amer Group, central Nunavut, comprises four dominantly sedimentary sequences (Ps1 through Ps4) deposited unconformably on Archean basement of the Rae sub-province. Ps1 is characterized by Ayagaq fm. quartzites formed in a stable cratonic and/or marine setting, with minor conglomerate and/or a distinctive schist at its base. PS2 is a sharply transgressive sequence of graphitic siltstone (Resort Lake fm.) shallowing up to dolostone (Aluminium River fm.) and intercalated to overlying porphyritic basalt (Five Mile Lake fm.). Ps3 comprises three units recording an overall coarsening- then shallowing-upward sequence involving siltstone to feldspathic arenite (Three Lakes, Oora Lake and Showing Lake formations). Ps3 is the primary host of U-mineralization in this region. Ps4 arkose (Itza Lake fm.) is preserved as isolated occurrences above a profound unconformity. The Amer Group is intensely deformed. D1 produced multiple transposition (three fold generations) and displacement along discrete detachments resulting in sub-horizontal axial surfaces and tectono-stratigraphy. D2 generated the regional, generally upright synclinoria, and is separated from D1 by the Ps3-Ps4 unconformity. Late D3 folds with sub-horizontal axial surfaces are rare. The region is transected by arrays of ENE- and NW- trending faults.
Elucidation of the structure of Ps3 units is central to determining the distribution of U-mineralization in the Amer Group. The difficulties of dealing with a polydeformed terrane are exacerbated by the absence of exposure in critical areas. This problem has been overcome by integrating detailed outcrop examination with high-resolution aeromagnetic data, and legacy drill hole data. The analysis is dependent on the strong, but distinct magnetic responses of the euhedral disseminated magnetite-bearing fine siliciclastic Three Lakes and Showing Lakes formations that, in preserved stratigraphic sequences, are separated by the Oora Lake fm. The aforesaid approach has enabled identification of a consistent, yet distinctly different geometry for the Amer Group "basins". In contrast to the apparent straightforward structure of the regional D2 synclinoria, it is demonstrated that the D1 tectono-stratigraphy forms large, regional recumbent structures masked by the lack of outcrop, but for which evidence occurs at all scales and within separate data sets i.e. field, geophysics, drill hole. The occurrence in some areas of elongate "cigar-shaped" mineralized zones reflects U-concentration within D1 hinge zones coaxially overprinted by D2. The success of this study in integrating diverse data bases, especially high-resolution geophysics and detailed outcrop mapping, argues for the future extension of such approaches.
Summary(Plain Language Summary, not published)
The uranium-hosting Paleoproterozoic Amer Group is some 150km north of Baker Lake, NU. It comprises four sedimentary sequences (Ps1 through Ps4), with Ps2 including tholeiitic basalt. The Archean basement, and Ps1 through Ps3 underwent early multi-phase translational deformation, dislocation and isoclinal folds including northeast directed sheaths. Several subsequent deformations affected Ps4 and the older rocks, with D2 creating the macroscopic map structures. D1 and D2 folds and lineations share the same orientation in many places, and the cigar-shaped disseminated uranium prospects have this southwesterly plunging attitude as well.

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