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TitleFe and Mg signatures of the Bong Uranium Deposit, Thelon Basin, Nunavut
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AuthorPotter, E G; Sharpe, R; Girard, I; Fayek, M; Gammon, P; Quirt, D; Robbins, J
SourceTargeted Geoscience Initiative 4: unconformity-related uranium systems; by Potter, E G (ed.); Wright, D M (ed.); Geological Survey of Canada, Open File 7791, 2015 p. 52-60, https://doi.org/10.4095/295783 (Open Access)
Year2015
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
RelatedThis publication is contained in Potter, E G; Wright, D M; (2015). Targeted Geoscience Initiative 4: unconformity-related uranium systems, Geological Survey of Canada, Open File 7791
File formatpdf
ProvinceNunavut
NTS66A; 66B
AreaSissons Lake
Lat/Long WENS -99.0000 -97.0000 64.7500 64.2500
Subjectsstructural geology; radioactive minerals; geochemistry; unconformity-type deposit; unconformities; uranium deposits; uranium; mineral deposits; mineral occurrences; mineralization; iron geochemistry; magnesium geochemistry; structural features; faults; alteration; hydrothermal alteration; illite; Athabasca Basin; Bong deposit; Kiggavik deposit; Thelon sub-basin; Woodburn Lake group
Illustrationslocation maps; photographs; cross-sections; profiles
ProgramUranium Ore Systems, Targeted Geoscience Initiative (TGI-4)
Released2015 03 02 (08:30)
AbstractThe Bong deposit is one of several uranium occurrences located ca. 5 km southeast of the faulted margin of the Proterozoic Thelon sub-basin, within altered metasedimentary rocks of the Woodburn Lake group. The deposit exhibits features in common with unconformity-related deposits of the Athabasca Basin, in particular a spatial association with the regional unconformity, alteration and ore mineralogy and structural context. Primary uranium enrichment is associated with a broad hydrothermal alteration halo characterized by an inner illite-rich zone and an outer chlorite-rich zone. Whole rock and clay-sized fraction ?57FeIRMM-014 and ?26MgDSM-3 values of the least-altered host rocks cluster near 0 ‰, within range of average values of crustal materials. Zones characterized by intense illite alteration have high ?57Fe and ?26Mg values, with average whole-rock values of ?57Fe = 0.87 }0.23‰ and ?26Mg = 0.61 }0.29‰, and clay-size fraction values of ?57Fe = 0.77 }0.29‰ and ?26Mg = 0.82 }0.09‰. These isotopic values correlate with reductions in Fe2+ concentrations (average of 0.47 mol. % versus average of 2.30 mol. % Fe2+ in least-altered hosts). The high ?57Fe values support leaching of Fe2+ (aq) with low ?57Fe compositions from the system, causing precipitation of iron-bearing minerals with ?57Fe values higher than the host rocks. The ?57Fe values may have been locally influenced by the formation of hematite and Fe-oxyhydroxide minerals in secondary miniature roll-front mineralization due to redox reactions. The high ?26Mg values coincide with formation of illite, which preferentially incorporated heavier magnesium isotopes during the intense hydrothermal alteration observed in both the ore zone and an upper hematitic horizon. Despite the significant shifts in isotopic compositions, the net iron depletion in the ore zone via selective leaching of Fe2+ without Fe3+ enrichment implies that redox reactions were not the dominant mechanism of primary uranium mineralization at the Bong deposit. Mineralogical and geochemical data support primary uranium precipitation through reduction and neutralization of an oxidized, acidic fluid. As Fe2+ was leached from the system in solution, enrichment of Fe-oxides and low whole-rock ?57Fe values may be a distal signature of these systems.
GEOSCAN ID295783