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TitreGraphite-bearing and graphite-depleted basement rocks in the Dufferin Lake zone, south-central Athabasca Basin, Saskatchewan
TéléchargerTéléchargement (publication entière)
AuteurPascal, M; Ansdell, K M; Annesley, I R
SourceTargeted Geoscience Initiative 4: unconformity-related uranium systems; par Potter, E G (éd.); Wright, D M (éd.); Commission géologique du Canada, Dossier public 7791, 2015 p. 83-92, (Accès ouvert)
ÉditeurRessources naturelles Canada
Documentdossier public
Mediaen ligne; numérique
Référence reliéeCette publication est contenue dans Potter, E G; Wright, D M; (2015). Targeted Geoscience Initiative 4: unconformity-related uranium systems, Commission géologique du Canada, Dossier public 7791
Lat/Long OENS-108.0000 -107.5000 57.5000 57.2500
Sujetsgîte de type discordance; discordances; gisements d'uranium; uranium; gisements minéraux; gîtes minéralogiques; minéralisation; géologie du socle; graphite; pétrographie; Bassin d'Athabasca ; géologie économique; minéraux radioactifs
Illustrationslocation maps; photographs; cross-sections; plots
ProgrammeÉtude des gîtes d'uranium, Initiative géoscientifique ciblée (IGC-4)
Diffusé2015 03 02 (08:30)
Résumé(disponible en anglais seulement)
Unconformity-type uranium deposits from the Athabasca Basin are interpreted to be the result of mixing between oxidized basinal brines and basement-derived reduced fluids/gases, and/or reduced basement rocks. Graphite and/or its breakdown products may be responsible for uranium mineralization by acting as a reductant that could trigger deposition of uranium. Also, graphite is considered to be indicative of basement structures as it is often concentrated along structures which can be identified as electromagnetic conductors. Underlying the sedimentary rocks of the basin in the Dufferin Lake zone (south-central Athabasca Basin) are variably graphitic pelitic schists (VGPS), which are altered to chlorite and hematite (Red/Green Zone: RGZ), and locally bleached (BZ) near the unconformity. These “graphite-depleted zones” contain rocks which are similar in texture to the VGPS, and are assumed to have contained graphite prior to alteration. The major element composition of the VGPS and RGZ are similar, but the RGZ and BZ are characterized by lower concentrations of carbon and sulphur. The BZ also has higher concentrations of uranium and boron. Raman analyses indicate that well-ordered carbon species (graphite to semi-graphite) are present in the VGPS, with both types more common within shear zones. In contrast, only rare low-ordered carbon species (carbonaceous matter) were detected in the graphite-depleted samples within the RGZ. Secondary fluid inclusions (FI) examined in different quartz vein generations provide an indication of the fluids that have interacted with the basement rocks. Monophase vapor, dominated by CH4 and N2 as identified by Raman, are the most common type of fluid inclusion in the VGPS, whereas aqueous two-phase (L+V) and three-phase (L+V+Halite) FI occur in the RGZ. The latter are rich in NaCl and CaCl2 and are similar to brines identified elsewhere in the basin.
Overall, several events are considered to be potentially responsible for graphite consumption. However, the most important processes likely occurred during retrograde metamorphism, and during fluid-rock interactions that ultimately created the RGZ and BZ. CH4 can be generated by the breakdown of graphite during hydration reactions and/or cooling of C-O-H fluids, and N2 could have been generated by the breakdown of ammonium (NH4 +)-bearing feldspar and micas. Basinal brines that circulated through the RGZ could also have broken down graphite and sulphides, and released gases/fluids into the sedimentary rocks of the basin. However, the absolute timing of graphite consumption is not known, and so the direct link with uranium deposition remains unclear.