DISTRIBUTION OF URANIUM IN GRANITES AND MOBILITY OF URANIUM DURING LOW-TEMPERATURE ALTERATION PROCESSES

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Date
1989-09
Authors
Bala, Bello Muhammad Dewu
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Abstract
The Nigerian Younger Granites are significantly enriched in U. The medium-grained types are more enriched in U than the coarsegrained varieties. It was found that U and Th are well correlated in the granites with an average Th:U ratio of 2.9. Both elements increase with increasing fractionation of the granites, but U abundance was subsequently greatly modified by late- and postmagmatic alteration processes. Potash metasomatism was observed to be associated with U depletion in the granites. The high U abundance and its geochemical associations suggests that the granites form a U province with the likely occurrence of veincontrolled U mineralisation in addition to the disseminated U-Sn mineralisation. Most of the U in the granites is held in U-rich minerals. These minerals account for over 80% of the whole-rock U. Among these, uranothorite and some Rare Earth minerals have been identified, with the possible occurrence of large amounts of uraninite. Radioactive accessory minerals that also contribute to the whole-rock U abundances in the granites are, zircon, allanite, sphene, apatite, monazite, rutile and thorite. Zircon, allanite and sphene are especially common. Most of the U in the near-surface environment has been remobilised, such that in surface samples only only resistate minerals are preserved. During weathering, U has
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Submitted by Bala Bello Muhammad Dewu to the University of Exeter as a Dissertation for the degree of Doctor of Philosophy in the Faculty of Science. I certify that all material in this thesis which is not my own work has been identified and that no material is included for which a degree has previously been conferred upon me. September, 1989
Keywords
DISTRIBUTION,, URANIUM,, GRANITES,, URANIUM,, LOW-TEMPERATURE,, ALTERATION PROCESSES
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