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Paragenesis, mineral chemical and microtextural studies of uranium bearing minerals in the brecciated albitites U-ores from the Kitongo shear zone, Poli region, northern Cameroon

Abstract : The Kitongo uranium deposit is located in the northwestern margin of the post-tectonic alkaline batholith of Kogué emplaced at ca. 550-530 Ma. The hydrothermal alteration system that affected the Kitongo granite is manifested by two albitization events characterized by the development of aegirine-albitites (Na-metasomatites). These albitization events that occurred respectively as pre-ore and ore stages were continuous, spacially bound one another and were accompanied by calcitization (Ca-metasomatites) and hematitization of various intensity. Tectonic breccias that were formed during the reactivation of wrench faults represent the most prevelent U-ore morphology types developed along the Kitongo shear zone (KSZ). These breccias were investigated for their mineral paragenesis, mineral chemical and microtextural features of uranium bearing phases. The results reveal that U-ore phases are spherical with a mineral nucleus, massive aggregates or in veinlets with some of these U-minerals showing areas of various brightness suggesting a heterogeneous composition of U-mineral phases. Radiation damage aureoles develop around idiomorphic uraninite crystals as a result of alpha radiations on the enclosing magnetite. The gangue minerals consist of albite, riebeckite, aegirine, amphibole, monazite, magnetite, calcite, zircon, epidote, apatite and titanite. U-ore phases are heterogeneous and represent complex U-ore mineral assemblage in which both primary and secondary uranium phases were observed. Uraninite, the primary uranium mineral occurred in the form of isolated euhedral to subhedral grains. It showed low SiO2, CaO, FeO, P2O5, ZrO2, ThO2 and Al2O3. The low ThO2 content in this uraninite grains indicated that U-primary mineralization formed at a relatively low temperature. Uraninite grains were progressively converted to coffinite. This progressive conversion was manifested by the occurrence of coffinitised U-phase. Coffinite occurred both as replacement or vein type U-phase however with no apparent chemical difference. The other U-phases include U-Zr-Si, U-Fe-Si and U-Ti. Overall, the physical and geochemical characteristics of the U-bearing phases in the studied breccias suggest alternating oxidizing and reducing conditions during the formation of uranium ore that occurred during the second albitization phase along the KSZ.
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Submitted on : Monday, July 4, 2022 - 11:26:30 AM
Last modification on : Tuesday, August 2, 2022 - 4:02:32 AM

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Arnaud Patrice Kouske, Martine Gerard, Jacques Etame, Ngouo Sylvestre Kanouo, Milan Stafford Tchouatcha, et al.. Paragenesis, mineral chemical and microtextural studies of uranium bearing minerals in the brecciated albitites U-ores from the Kitongo shear zone, Poli region, northern Cameroon. International Journal of Earth Sciences, 2022, 111, pp.1413-1436. ⟨10.1007/s00531-022-02186-1⟩. ⟨insu-03712805⟩

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