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TitleBasement to surface expressions of deep mineralization and refinement of critical factors leading to the formation of unconformity-related uranium deposits
AuthorPotter, E GORCID logo
SourceInternational Symposium on Uranium Raw Material for the Nuclear Fuel Cycle: Exploration, Mining, Production, Supply and Demand, Economics and Environmental Issues (URAM 2014), abstracts; 2014.
Alt SeriesEarth Sciences Sector, Contribution Series 20130508
PublisherInternational Atomic Energy Agency (IAEA)
MeetingInternational Symposium on Uranium Raw Material for the Nuclear Fuel Cycle: Exploration, Mining, Production, Supply and Demand, Economics and Environmental Issues (URAM 2014); Vienna; AT; June 23-27, 2014
RelatedThis publication is related to Basement-to-surface expressions and critical factors in the genesis of unconformity-related uranium deposits
File formatpdf
ProvinceSaskatchewan; Northwest Territories; Nunavut; Quebec
NTS74H; 66A; 32P/09; 32P/16
AreaKey Lake; McArthur River; Thelon River; Camie River
Lat/Long WENS-106.0000 -104.0000 58.0000 57.0000
Lat/Long WENS -98.0000 -96.0000 65.0000 64.0000
Lat/Long WENS -72.5000 -72.0000 52.0000 51.5000
Subjectseconomic geology; geochemistry; geochemical anomalies; uranium; uranium deposits; mineralization; mineral deposits; geochemical analyses; sedimentary rocks; sandstones; unconformities; unconformity-type deposit; alteration; basement geology; Athabasca Basin; Phoenix Deposit; Millennium Deposit; McArthur River Deposit; Dufferin Lake zone; Thelon Basin; Bong deposit; Otish Basin; Camie River deposit; Precambrian
ProgramTargeted Geoscience Initiative (TGI-4) Uranium Ore Systems
ProgramTargeted Geoscience Initiative (TGI-4) Uranium Ore Systems
AbstractUnder the Targeted Geoscience Initiative Four (TGI-4) program operated by the Geological Survey of Canada, a collaborative project between government, academia and industry is examining unconformity-related U ore systems in the Proterozoic Athabasca (Phoenix, Millennium McArthur River and Dufferin Lake zone), Thelon (Bong) and Otish (Camie River) basins in order to refine genetic models and exploration tools for these U deposits.
Examination of basement graphite-depleted zones underlying U-bearing zones at the Dufferin Lake zone has revealed the presence of low-ordered carbon species (carbonaceous matter) that may be interpreted as products of graphite consumption (± later carbon precipitation) by oxidizing Athabasca Basin fluids that migrated downward into the basement. This may have produced a mobile reductant (gas or fluid), which could then have played a role in deposition of UO2. Alternatively, new numerical modelling supports a previous hypothesis that fluid overpressures may have caused hydrocarbons generated from oil shale at the top of the Athabasca Group to migrate downwards to the sites of U precipitation. A preliminary Fe and Mg isotopic study of the basement-hosted Bong deposit revealed that high ?57Fe and ?26Mg values are associated with U-bearing illite+chlorite alteration and a bright red hematitic zone that is often ascribed to 'paleoweathering' in the literature. The higher isotopic values correlate with depletions in molar Fe2+, indicating that the processes that formed both alteration zones mobilized Fe2+ while enriching the exiting fluids in the lighter isotopes of Fe and Mg.
Petrological, geochemical and isotopic studies of intense alteration concentrated along the P2 fault hosting the McArthur River deposit reaffirm previous studies that the alteration overprinted earlier paleoweathered and diagenetic altered horizons along the unconformity and that the fault served as a conduit for basinal fluids to modify basement rocks through fluid-rock interactions. This fault-control is also manifested regionally, with new 3D modeling of the unconformity surface highlighting the influence of northeast-trending reverse faults in formation of a narrow ridge between the Phoenix and McArthur River deposits. Regional clay anomalies documented in previous studies, associated with the majority of deposits and prospects, are also broadly aligned with this feature.
Athabasca Group sandstones overlying the Phoenix deposits show relatively high concentrations of U, B, Pb, Ni, Co, Cu, As, Y and REEs above the deposit up to the uppermost sandstones and along the ore-hosting WS shear zone. In support of previous studies, some of the metals (U, Mo, Co, Ag and W) also occur in elevated concentrations in humus and B-horizon soil overlying the Phoenix and Millennium deposits. However, these new results enhance the sensitivity of these surficial geochemistry detection methods for deeply buried (ca. 600'750 m) uranium deposits. The locations of these anomalously high metal concentrations coincide with surface projections of the reactivated shear zones, consistent with the fault conduit model. Elevated concentrations of the U decay product 4He in groundwater overlying the deeply buried Millennium deposit also supports this model.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. This conference presentation summarizes key results of the TGI-4 uranium ore systems project that is focused on unconformity-related uranium deposits. Using examples from Saskatchewan, Nunavut and Quebec, the results further refine the ore deposit models (defining the role of graphite underlying the deposits, iron plus magnesium isotope signatures and 3D modelling), enhance existing exploration tools (surficial geochemistry) and outline potential new exploration tools (i.e. helium in groundwater) for these highly prospective deposits.

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