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TitleBasement geology beneath the northeast Thelon Basin, Nunavut: Insights from integrating new gravity, magnetic and geological data
AuthorTschirhart, V; Jefferson, C W; Morris, W A
SourceGeophysical Prospecting vol. 65, issue 2, 2016 p. 617-636,
Alt SeriesEarth Sciences Sector, Contribution Series 20140338
PublisherJohn Wiley & Sons
Mediapaper; on-line; digital
File formatpdf
ProvinceNunavut; Northwest Territories
NTS66G/02; 66G/03; 66G/04; 66G/05; 66G/06; 66G/07
AreaThelon Basin; Baker Lake
Lat/Long WENS-100.0000 -98.0000 65.0000 64.0000
Subjectsuranium deposits; basement geology; unconformity-type deposit; geophysical interpretations; Archean Woodburn Lake group; Marjorie Hills; Amer Mylonite Zone; Nueltin igneous rocks; Pitz formation
Illustrationsgeological sketch maps; location maps; stratigraphic charts; tables; magnetic maps; schematic cross-sections
ProgramRae Province Project Management, GEM2: Geo-mapping for Energy and Minerals
AbstractCurrent models for unconformity-associated uranium deposits predict fluid flow and ore deposition along reactivated faults in >1.76 Ga basement beneath Mesoproterozoic siliciclastic basins. In frontier regions such as the Thelon Basin in the Kivalliq region of Nunavut, little is known about the sub-basin distribution of units and structures, making exploration targeting very tenuous. We constructed a geological map of the basement beneath the unconformity by extrapolating exposed features into the subsurface. The new map is constrained by detailed geological, geophysical, and rock property observations of outcrops adjacent to the basin and by aeromagnetic and gravity data over the geophysically transparent sedimentary basin. From rock property measurements, it is clear that the diverse magnetic and density characteristics of major rock packages provide quantitative three-dimensional constraints. Gravity profiles forward modelled in four cross sections define broad synforms of the Amer Belt and Archean volcanic rocks that are consistent with the structural style outside the basin. Major lithotectonic entities beneath the unconformity include: supracrustal rocks of the Archean Woodburn Lake group and Marjorie Hills meta sedimentary gneiss and associated mixed granitoid and amphibolitic gneiss; the Amer Mylonite Zone and inferred mafic intrusions oriented parallel and sub-parallel; other igneous intrusions of 2.6 Ga, 1.83 Ga, and 1.75 Ga vintage; and the <2.3 Ga to >1.84 Ga Amer Group. Four main brittle regional fault arrays (040° - 060°, 075° - 90°, 120°, and 150°) controlled development and preservation of the basin. The reactivated intersections of such faults along fertile basement units such as the Rumble assemblage, Marjorie Hills assemblage, Nueltin igneous rocks, and Pitz formation are the best targets for uranium exploration.
Summary(Plain Language Summary, not published)
The ultimate goal of the NE Thelon consortium (LOA among 9 companies, McMaster U and NRCan) was to integrate new geophysical and geological data and extend knowledge of surrounding hard rock geology beneath flat lying sandstone called the Aberdeen Sub-basin. The <1.75 billion year old sandstone hides the hard rock, but gravity and magnetic data can see through, it to remotely predict what lies beneath. Six main rock belts were tracked under an area the size of SE Ontario. Three of these belts contain uranium occurrences outside the basin, so are favourable trends for exploration beneath it. Gravity data also constrained sandstone thickness (a key cost factor for exploration drilling) and five regional fault arrays (sets of near-vertical fractures where the rocks moved up or down on opposite sides) that controlled how the Aberdeen Sub-basin sank, was filled with river sand, and where hot groundwater circulated and was focused to form uranium deposits.