Geological Setting, Petrology, and Geochemistry of Granitic Pegmatites and Leucogranites Hosting U-Th-REE Mineralization at Fraser Lakes Zone B, Wollaston Domain, Northern Saskatchewan, Canada

Abstract The U-Th-REE mineralization at Fraser Lakes Zone B is hosted by granitic pegmatites and leucogranites, which lie along the deformed contact between Paleoproterozoic metasedimentary gneiss of the Wollaston Group and Archean orthogneiss, approximately 25 km from the southeastern edge of the Athabasca Basin. The pegmatites/leucogranites are subcordant to concordant with the regional foliation and are concentrated within a northeast-plunging antiformal fold nose, the study area, which lies west of Fraser Lakes. The mineralized pegmatites/leucogranites in the western part of the study area (Group A) are typically enriched in U (± Th) with Th/U ~1, and contain uraninite, thorite, zircon, and allanite. Those intruding the central part of the study area (Group B) are generally enriched in Th and LREE, with Th/U >2, and contain monazite, thorite (commonly U-enriched), and zircon. The pegmatites and leucogranites in Group A tend to be slightly enriched in SiO2 and depleted in TiO2 relative to those in Group B and are interpreted to represent more evolved crustal melts. Both groups are peraluminous and show varied chemistry. Partial melting (~850ºC and 9 kbar) of a metasedimentary rock-dominated source, entrainment of accessory minerals as xenocrysts, and assimilation–fractional crystallization processes combined to enrich the granitic pegmatites/leucogranites in U, Th, and REE elements. Transfer of melt from the source region to the crystallization sites was assisted by deformation within and along major structural zones, such as the folded Archean–Paleoproterozoic discontinuity. The character of mineralization and structural control in the study area is reminiscent of the alaskite-hosted deposits at Rössing, Namibia.
Keywords: U-rich pegmatites, Th-REE-rich pegmatites, Fraser Lakes Zone B, Wollaston Domain, Athabasca Basin, U metallogeny
Résumé La minéralisation en U-Th-ÉTR de la Zone B de Fraser Lake est contenue dans des pegmatites granitiques et des leucogranites localisés le long du contact déformé entre des gneiss métasédimentaires d’âge paléoprotérozoïque du Groupe de Wollaston et des orthogneiss d’âge archéen, à environ 25 km de l’extrémité sud-est du bassin d’Athabasca. Les pegmatites / leucogranites sont subcordants à concordants avec la foliation régionale et se concentrent dans la charnière d’un antiforme plongeant vers le nord-est dans la zone d’étude, laquelle est située à l’ouest de Fraser Lake. Les pegmatites minéralisées / leucogranites de la partie ouest de la zone d’étude (Groupe A) sont généralement enrichis en U (Th ±), présentent un rapport Th / U ~ 1, et contiennent de l’uraninite, de la thorite, du zircon et de l’allanite. Celles faisant intrusion dans la partie centrale de la zone d’étude (groupe B) sont généralement enrichies en Th et en terres rares légères, avec un rapport Th / U > 2, et contiennent de la monazite, de la thorite (communément enrichie en U), et du zircon. Les pegmatites et les leucogranites du groupe A tendent à être légèrement enrichis en SiO2 et appauvris en TiO2 par rapport à ceux du groupe B et proviendraient de liquides plus évolués d’origine crustale. Les deux groupes sont hyperalumineux et présentent des compositions chimiques variées. La fusion partielle (à ~ 850 ° C et à 9 kbar) d’une source dominée par des roches métasédimentaires s’est combinée à l’entraînement de minéraux accessoires en tant que xénocristaux, ainsi qu’aux processus d’assimilation et de cristallisation fractionnée expliquerait l’enrichissement des pegmatites granitiques / leucogranites en U, Th, et en éléments des terres rares. La déformation à l’intérieur et en périphérie de zones structurales majeures, tel la discordance plissée entre l’Archéen et le Paléoprotérozoique, a contribué à la migration des liquides de fusion partielle de la région source aux sites de cristallisation. La nature de la minéralisation et le contrôle structural dans la zone d’étude rappellent les gîtes contenus dans des alaskites à Rössing, en Namibie.
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Summary: We use the results of new bedrock mapping, combined with geochemical point data and airborne radiometric data (in particular equivalent uranium concentrations) to help determine which geological units in the Paleoproterozoic Great Bear magmatic zone (GBmz) contain elevated uranium. The data collectively indicate that the highest primary uranium concentrations are in equigranular granites and subvolcanic/volcanic porphyries. Notably, these rocks host the majority of known uranium-bearing...
Publication: Exploration & Mining Geology
Author(s): LUKE OOTES, JEFF HARRIS, VALERIE A. JACKSON, BRONWYN AZAR, AND LOUISE CORRIVEAU
Keywords: Wopmay orogen, Great Bear magmatic zone, bedrock geochemistry, IOCG, unconformityrelated uranium
Issue: 1
Volume: 21
Year: 2013
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Summary: A 10-cm thick clay-rich layer near the top of the Manitou Falls Formation of the Athabasca Group is unusual in its breccia texture, alteration, and detrital mineral composition relative to the adjacent overlying and underlying sedimentary beds. This layer is composed of angular quartz grains set in an illite >> kaolinite + dickite matrix. Deformed clay-rich fragments within the layer have very similar mineral assemblages. The presence of euhedral accessory minerals including Ti-oxides and...
Publication: Exploration & Mining Geology
Author(s): JEANNE B. PERCIVAL, SEAN A. BOSMAN, ERIC G. POTTER, PAUL RAMAEKERS, KATHERINE E. VENANCE, PAT A. HUNT, WILLIAM DAVIS, AND CHARLES W. JEFFERSON
Keywords: microbreccia, hydrothermal alteration, hydraulic fracturing, uranium mineralization
Issue: 1
Volume: 21
Year: 2013
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Summary: The nature and distribution of radiation-induced defects (RIDs) in quartz from the Maw Zone, a yttrium- and rare-earth-element-enriched sandstone breccia complex exhibiting intense hydrothermal alteration, have been investigated by electron paramagnetic resonance (EPR) spectroscopy. EPR spectra show that detrital quartz in sandstone, from five diamond drill holes intersecting the Maw Zone and one above the crest of the so-called Quartzite Ridge, contain only background-level RIDs, indicating...
Publication: Exploration & Mining Geology
Author(s): YUANMING PAN, GARY YEO, BRETT ROGERS, CHRISTINE AUSTMAN, AND BAOQUAN HU
Keywords: quartz EPR, radiation-induced defects, hydrothermal alteration, uranium exploration, Athabasca Basin
Issue: 1
Volume: 21
Year: 2013
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Summary: The use of CR-39 plastic polymer as a solid state nuclear track detector in the textural analysis of radioactive minerals in geological samples was first described by I.R Basham in 1981. CR-39 autoradiographs provide a detailed, high-resolution image of the in situ distribution of the radioactive minerals within geological samples on both the macroscopic and microscopic scales. This technique is an inexpensive and effective means of obtaining detailed textural information that provides...
Publication: Exploration & Mining Geology
Author(s): G.W. SPARKES
Keywords: uranium, CR-39, autoradiograph, Labrador, uraninite
Issue: 1
Volume: 21
Year: 2013
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Summary: A new method for mapping faults within basement rocks underlying the Thelon Formation and glacial overburden was developed and tested in the Aberdeen Sub-basin. This method utilizes newly acquired aeromagnetic data, the Blakely algorithm for defining magnetic source edges, a calculated dip-direction map, a digital elevation model (DEM) derived from the Canadian Digital Elevation Database, and the positions of identified, inferred and newly mapped faults that are within and adjacent to this...
Publication: Exploration & Mining Geology
Author(s): VICKI TSCHIRHART, BILL MORRIS, AND CHARLES JEFFERSON
Keywords: faults, uranium, Thelon Basin, source edge detection, lineament analysis
Issue: 1
Volume: 21
Year: 2013
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Summary: The Dragon Lake Zone (uranium prospect) comprises a N160º trending vein that is approximately 110 m long, up to 5 m wide and from 1 to 40 m high. The zone is mostly within altered sandstone of the Fair Point Formation, the basal unit of the Paleoproterozoic Athabasca Group, but it also extends downward (up to 3.5 m) into basement rocks that occupy the northerly trending Maybelle River Shear Zone (MRSZ). This subvertical shear zone separates graphitic paragneiss and weakly deformed granitoid...
Publication: Exploration & Mining Geology
Author(s): K. WHEATLEY AND C. CUTTS
Keywords: uranium, unconformity, Alberta, Maybelle River, Dragon Lake, Athabasca
Issue: 1
Volume: 21
Year: 2013
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Summary: Lac Cinquante is a mineralogically simple, vein-hosted uranium deposit in Archean basement rocks (Angikuni greenstone belt) that originally were unconformably overlain by Proterozoic sedimentary and volcanic rocks of the Baker Lake Group (BLG). Basement rocks are mainly pillowed and massive tholeiitic lavas (N-MORB) with interbedded tuff; overlying sedimentary rocks comprise a basal talus/fault breccia that grades upward into fluvial sedimentary rocks and subaerial, trachytic volcanic rocks;...
Publication: Exploration & Mining Geology
Author(s): N.J. BRIDGE, N.R. BANERJEE, S. PEHRSSON, M. FAYEK, C.S. FINNIGAN, J. WARD, AND A. BERRY
Keywords: NW Hearne, Archean basement, Baker Lake Group, Angikuni subbasin, vein-hosted uranium, graphite
Issue: 1
Volume: 21
Year: 2013
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