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Caractéristiques pétrographiques et géochimiques et évolution diagénétique des bassins silicoclastiques mésoprotérozoïques intracontinentaux : Implications sur la genèse des gisements d'uranium de type discordance

Abstract : A mineralogical, petrographic and geochemical study of the proterozoic siliciclastic sedimentary intracontinental basins of Waterberg (Kaapvaal Craton, South Africa), Cariewerloo (Gawler Craton, South Australia), Satakunta and Muhos (Fennoscandian Shield, Finland), unconformably overlying archaean and paleoproterozoic basement, have been characterized and compared with other districts throughout the world similar in age and lithology (the basin of Athabasca in Canada, the basin of Kombolgie in Australia, and the basin of Pasha-Ladoga in Russia) which are associated with uranium ore deposits. The realized study made it possible to reconstitute the nature of the detrital phases and their evolution during diagenesis and hydrothermal events, in order to evaluate the interests that represent the sediments of these basins for the exploration of uranium by reference to strongly mineralized Athabasca and Kombolgie basins. This study shows that the clastic rocks of all of these basins are characterized by a high immaturity of sedimentary materials, a strong oxidation, as well as a diagenesis or a metamorphism of high temperature. These sediments, rich in potassic feldspar and plagioclase with frequently angular clasts, were transported over a short distance from the source area and subjected to a limited pedogenic alteration in a very active tectonic context, contrary to the sediments of the Athabasca and Kombolgie basins. However, significant fluid circulations took place as shown by the presence of an argillaceous alteration on the roof of the basement of the Cariewerloo, Satakunta and Muhos basins, as the argillaceous alteration. This alteration remains however moderate compared to that observed in the Athabasca and Kombolgie basins. These fluid circulations are related to zircon alterations, and essentially to the formation of Fe-chlorite and carbonate.
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Ahlam Ibrahim. Caractéristiques pétrographiques et géochimiques et évolution diagénétique des bassins silicoclastiques mésoprotérozoïques intracontinentaux : Implications sur la genèse des gisements d'uranium de type discordance. Sciences de la Terre. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10086⟩. ⟨tel-01748255⟩

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