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TitleComposition of large zoned Aluminium phosphate sulfate minerals: Implications for fluid evolution in the centennial Uranium deposit area, Athabasca Basin, Saskatchewan, Canada
AuthorReid, K D; Ansdell, K; Creighton, S; Potter, E G
SourceCanadian Mineralogist vol. 54, no. 5, 2016 p. 1205-1228,
Alt SeriesEarth Sciences Sector, Contribution Series 20150089
PublisherMineralogical Association of Canada
Mediapaper; on-line; digital
File formatpdf
ProvinceAlberta; Saskatchewan
NTS64E; 64L; 64M; 74E; 75F; 75G; 75H; 75I; 75J; 75K; 75L; 75M; 75N; 75O; 75P
AreaAthabasca Basin
Lat/Long WENS-112.0000 -104.0000 60.0000 57.0000
Subjectsmetallic minerals; regional geology; mineralogy; aluminum; aluminum geochemistry; phosphate; sulphate; mineral occurrences; alunite; kaolinite; illite; hydrothermal deposits; regoliths; alteration; alteration products; mineralization; mineralogical analyses; uranium; Rae Province; Carswell Formation; Douglas Formation; Otherside Formation; Locker Lake Formation; Wolverine Formation; Lazenby Lake Formation; Manitou Falls Formation; Fair Point Formation
Illustrationslocation maps; geological sketch maps; cross-sections; tables; photomicrographs; plots
ProgramSouth Rae Province Bedrock/Surficial geology, GEM2: Geo-mapping for Energy and Minerals
AbstractAluminum phosphate sulfate (APS) minerals associated with the Athabasca Basin are compositionally part of the alunite group. Typically 5 - 20 um in size, they accompany the regional diagenetic-hydrothermal illite-kaolinite-dickite assemblage in the Athabasca Group sandstones, the illite-sudoite assemblage of the altered paleo-regolith, and alteration zones surrounding uranium deposits. In the vicinity of the Centennial deposit, where illite and sudoite replace coarse-grained aluminosilicate porphyroblasts in the basement phyllitic pelites, cubic APS crystals are as large as 80 ?m. Detailed petrography indicates that the APS crystals form broadly coeval to illite. Backscattered electron imaging, elemental mapping, and compositional analysis reveal complex zoning as well as later hydrothermal alteration of the APS crystals. Growth-zoned crystals are a solid solution between crandallite-goyazite-svanbergite [Sr0.17 - 0.32Ca0.0.18 - 0.28LREE0.0.25 - 0.46(Al2.78 - 2.92Fe0.01 - 014)(PO4)1.82 - 2.03(SO4)0.14 - 0.35(OH)6], whereas the later alteration of the APS minerals results in a compositional shift to endmember florencite [Sr0.15Ca0.11LREE0.57(Al2.86Fe0.02)(PO4)1.98(SO4)0.15(OH)6]. Fluids responsible for the alteration of APS to florencite are paragenetically linked to late hydrothermal fluids associated with mafic Mackenzie dikes and do not appear to be related to proximity to uranium mineralization. Both zoned and altered portions of the crystals have bulk compositions that overlap with APS minerals in other areas of the basin suggesting a common genetic origin. However, it is critical to link the paragenetic context to observed compositional changes. An increase in MREE from early to late stages of zoned crystal growth correlates with the greatest concentration of REE found in uraninite from unconformity-related uranium deposits. This could be a link between broader APS growth and uraninite precipitation.
Summary(Plain Language Summary, not published)
Completed under phase I of the Geo-mapping for Energy and Minerals program, this study documents compositional variability of a key alteration mineral (aluminum phosphate sulphate or APS) formed during genesis of unconformity-related uranium deposits in the Athabasca Basin. Unlike previous studies, this work proposes that some of the compositional changes reflect later hydrothermal alteration, unrelated to the main ore-forming processes. Similar compositional changes in APS grains around uranium deposits and in 'apparently barren alteration haloes' suggests the effects of later mafic dyke driven hydrothermal activity in the Athabasca Basin could be more significant that previously considered and need to be considered when using APS chemistry in exploration.