La genèse des gisements de type roll front dans le bassin d'Erlian, Chine

Abstract : The Erlian Basin located in NE China developed during the late Mesozoic continental extension in eastern Asia. This basin lies on a basement corresponding to the eastern part of the Central Asia Orogenic Belt. Indosinian magmatism (236.8±5.8 Ma) is widely represented by high-K calcalkaline granites derived from an enriched mantle (low 143Nd/144Ndi; negative epsilon Nd(t)) and correspond to major U sources. Braided fluvial systems of post-rift sediments of the Erlian Basin correspond to favorable sedimentary conditions for the genesis of permeable and reduced sandstones. Post-rift sediments contain significant synsedimentary U concentrations, mainly adsorbed on clay minerals. These pre-concentrations are redistributed in situ, during the diagenetic evolution, and mineralized as coffinite and pitchblende replacing pyrite or pyritized OM (e.g. Nuheting). The OM occurring within these sediments is mainly terrigenous and corresponds to kerogens of type IV, thermally immature. Finally, the roll front-type Bayinwula deposit is characterized by a biogenic model involving reactions between OM, U-rich Fe/Ti oxides and sulfate-reducing bacteria. In the pyrite zone, the OM is degraded by bacteria and replaced by pyrite. H2S production contributes in the dissolution of Fe/Ti oxides that are progressively epigenized into pyrite, characterized by strongly negative values of delta 34S. U concentrations from Fe/Ti oxides and OM are liberated and can be leached by oxygenated groundwater. H2S creates a reducing barrier contributing in the reduction of uranium that precipitates at the redox front as coffinite and ningyoite
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Christophe Bonnetti. La genèse des gisements de type roll front dans le bassin d'Erlian, Chine. Sciences de la Terre. Université de Lorraine, 2013. Français. ⟨NNT : 2013LORR0282⟩. ⟨tel-01750627⟩

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