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