Mineralogy, geochemistry and ore genesis of Kanawa uranium mineralization, Hawal Massif, eastern Nigeria terrane: Implications for uranium prospecting in Nigeria and Cameroon

摘要

The Kanawa area, Eastern Nigeria Terrane (ENT), located proximal to Pan-African shear zone, has U prospects with an average U concentration of similar to 0.1 wt%. Samples taken from the fault breccia, mylonite, cataclasite and ore zone show increasing U contents of 2.2-6.7 ppm, 4-7 ppm, 36-253 ppm, and 165->1000 ppm, respectively. U-Pb dating of magmatic zircons from the granite hosting the U prospect yield Pb-206/U-238 concordia age of 603 +/- 5.9 Ma suggesting Pan-African (Ediacaran) age for the host granite. In contrast, zircon grains from the U-ore zone yield Pb-206/U-238 concordia age of 228 +/- 2 Ma, considered here as the estimated age of U mineralization, an interpretation that need to be supported by additional data. The Pan-African granite hosting Kanawa U mineralization has very low U content (U = 1.0-6.7 ppm) and therefore could not have been the main source of the U mineralization. Considering that the Kanawa U ore zone shows broadly similar geochemical signature and yield roughly similar age with its spatially associated Mesozoic rocks in area, we suggest that the U mineralization was probably sourced from the Mesozoic volcanics rocks. Uranium, Zr, V may have been leached out from the Mesozoic volcanic by hydrothermal fluid circulating along the channel ways provided by Pan-African wrench fault. Taken together, our combined major and trace element data in conjunction with previously reported data of U mineralization from western Cameroon allow us re-evaluate the geochemical signatures of Pan-African granite hosting U mineralization in these regions and reassess their U potential in relation to some well-known U deposits elsewhere in the world. It is noteworthy that the Kanawa U mineralization shows broadly similar geochemical features with the volcanic-related Streltsovskoye-Antei U deposit, Transbaikalia, Russia. The highly evolved Ekomedion granites in Cameroon have high U and F content and exhibit geochemical features typical of U-fertile granite suggesting that U mineralization Ekomedion area was probably sourced from the granites. In contrast, Pan-African granites from Kitongo have low U and F content and may not have been the primary source of the Kitongo U mineralization. As suggested for Kanawa U mineralization, the Kitongo U mineralization was probably sourced from the Mesozoic rocks in the area. These chains of Mesozoic volcanic and plutonic suites, largely emplaced within Pan-African mega-shear zones, extend from Nigeria into Cameroon and Niger, and could be linked to other mega shear zones in Egypt and Saudi Arabia where similar U mineralization have been reported. This study, therefore, allows for an initial correlation of U occurrences and provides a framework for further regional investigation.