| Summary: | The Aphebian aged Sosan Group consists dominantly of unmetamorphosed elastic sedimentary rocks within the lower part of the Great Slave Supergroup, in the East Arm graben, Crest Slave Lake, Canada. Fieldwork, petrographic techniques, X.R.D., X.R.F. and Gamma Ray Spectrometry were used to help unravel the stratigraphy, sedimentology and diagenesis (including the uranium mineralisation) of the Sosan Group. The Sosan Group is subdivided into the Hornby Channel, Duhamel, Kluziai and Akaitcho River Formation.The Hornby Channel Formation in the western East Arm is believed to be cut by the Easter Island dyke (dated at 2200 Ma), consists of a sequence of braided river deposits, and is considered to be earlier than the rest of the Hornby Channel Formation in the East Arm. In the central East Arm, towards the apparent source area of these sediments, this Formation consists of a sequence of shallow marine and coastal sandstones which grade to the northeast into a fluvial succession.The overlying Kluziai, Duhamel and Akaitcho River Formations are probably mostly of tidal channel, upper and lower tidal flat and alluvial plain origin. The facies vary widely, being dependent upon the supply of terrigenous sediment, depositional environment and, to varying extents, volcanism. The uranium mineralisation occurs as a cement within marine and fluvial sandstones of the Sosan Group, partially replacing mudetone clasts or mica, or as minor veinlets. The presence of detrital glauconite, jordisite and bravoite implies that the uranium deposits were formed at low temperatures. Oxidised ground waters migrating through the sandstones probably leached uranium and precipitated it at a reducing horizon. The latter may have developed as a result of trapped hydrocarbons within the sandstone.
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