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Evolution et origine des saumures dans les bassins protérozoïques au voisinage de la discordance socle/couverture : l'exemple de l'environnement des gisements d'uranium associés aux bassins Kombolgie (Australie) et Athabasca (Canada)

Abstract : The nature evolution and origin of ftuids that circulate at the basis of two Proterozoilc sandstone basins (Kombolgie and Athabasca) associated with unconformity type uranium mineralization have been characterised.Several techniques (mlcrothermometry, Raman, LlBS) were used to analyse individual fluid inclusions from different quartz generations. The couplinq of these techniques enabled to determine the composition of the paleofluids that are probably irnplied in the genesis of these uranium deposits.The P, T, x evolution of these fluids has been reconstructed. A common model! of fîuid circulation for the two basin is proposed : A chloride-rich sodlum dominated brins (15-20 wt% NaCl + 4-12 wt% CaCl2), highly oxidising (equilibrated with hematite) is responsible for the early diagenetic silicification. The circulation of a calcium-rich brine (25-3Owt.%CaCl2+0-10wt%NaCl)was responsible for the deposition of a secondary quartz and dravite in the sandstone at the emergence of the reverse faults. The calcium content of this brine results from the evolution of the sodic brine through Na-Ca exchange in the basement. A low salinity fluid, which was heated in the basement and which contains sorne traces of methane, dilutes the erines at the basis of the Kombolgie basin, during tectonic movements and hydraulic brecciation. This fluid has been rarely observed in the Canadian deposits. This study has shawn many similarities between the fluid regimes of the Kombolgie and Athabasca basins. ln bath districts, the evolution ofa sodium-rich brine towards a calcium-rich one and their subsequent mixing have been evidenced. Estimated temperatures (160+/-20°C) and depths (4-6 km) are similar for the two basins.Howeverthe brines observed at the basis of the Athabasca basin are slightly more concentrated than brines observed in the Kombolgie sandstone. The low salinity fluid was rarely observed in the Canadian deposits, where it was strongly ccntaminated by H2 and 02 produced by the radiolysis of water at the contact with uranium. This fluid does not show evidences of mixing with the brines. The uranium ore deposition in the Athabasca deposits seems to be rather asscciated with the interaction of the oxidised uranium bearing brines with the reducing basement lithologies than with the mixinq between the brines and a reducing fluid. However, the latter corresponds to the conditions of uranium ore deposition in the Australien deposits. One of the major parameters that may have controlled the importance of these deposits seems to be the ability of these thick, intracontinental and highly oxidised mid-Proterozoic detrital and evaporitic sedimentary basins to generate highly concenffated sodi-calcic chloride brines.
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http://docnum.univ-lorraine.fr/prive/SCD_T_2002_0230_DEROME.pdf
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https://hal.univ-lorraine.fr/tel-01746740
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Submitted on : Thursday, March 29, 2018 - 10:43:52 AM
Last modification on : Wednesday, November 4, 2020 - 1:56:02 PM

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  • HAL Id : tel-01746740, version 1

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Donatienne Derome. Evolution et origine des saumures dans les bassins protérozoïques au voisinage de la discordance socle/couverture : l'exemple de l'environnement des gisements d'uranium associés aux bassins Kombolgie (Australie) et Athabasca (Canada). Sciences de la Terre. Université Henri Poincaré - Nancy 1, 2002. Français. ⟨NNT : 2002NAN10230⟩. ⟨tel-01746740⟩

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