Le système métallogénique des gisements d’uranium associés à la faille d’Arlit (Bassin de Tim Mersoï, Niger) : diagenèse, circulations des fluides et mécanismes d’enrichissement en métaux (U, Cu, V)

Abstract : The main U-deposits of Niger (Arlit, Akouta, and Imouraren) are all located in the Tim Mersoï Basin, east of the Arlit Fault. The deposits of Arlit and Akouta are hosted in Carboniferous formations and have a substantially reduced uranium mineralization, while the Imouraren deposit is contained in a Jurassic formation in the form of predominantly oxidized uranium mineralization with some pockets of reduced mineralization. New ore bodies discoveries west of the Arlit Fault in the regions of Arlit and Akouta and the differences between the U-deposits in the Carboniferous and Jurassic, have encouraged a reevaluation of the previous metallogenic models. The objective is to determine whether the uranium mineralizations of Tim Mersoï Basin were formed during the same diagenetic/hydrothermal event in relation with a major geotectonic event, or if they are polyphase over time, in order to propose a general metallogenic model. A multi-technique approach involving a detailed study of diagenesis, fluid circulations, mineralization, geochronology and geothermometry was applied to trace the burial history of the basin and constrain the P-T conditions of uranium deposition. Two main phases of uranium mineralization are distinguished: (i) A diagenetic/hydrothermal episode between 100 and 135 Ma in which primary uranium and copper minerals precipitate in reduced environment under conditions close to maximum burial (P : 80-120 bars, T : 115-150 °C), in relation with Atlantic rift periods during Cretaceous. (ii) A serie of remobilizations of primary uranium minerals in oxidizing environment to form secondary uranium, vanadium and copper minerals under supergene conditions related to uplift since 50 Ma, during the major events of oxidation in western Africa.
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Marah Mamane Mamadou. Le système métallogénique des gisements d’uranium associés à la faille d’Arlit (Bassin de Tim Mersoï, Niger) : diagenèse, circulations des fluides et mécanismes d’enrichissement en métaux (U, Cu, V). Géologie appliquée. Université de Lorraine, 2016. Français. ⟨NNT : 2016LORR0231⟩. ⟨tel-01673827v2⟩

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