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4.6.2. Hydrothermal alteration and uranium mineralization
Following metamorphism and pre-ore alteration of the basement and diagenesis of
the overlying Coronation sandstone of the El Sherana Basin, the rocks were affected by the
main U mineralization event associated with an intense brecciation that is likely related to
tectonic reactivation along the El Sherana-Palette fault system (Lally and Bajwah, 2006).
Petrographic and textural observations indicate a spatial relationship between the intensity
of the pre-ore alteration and the location of the U mineralization. Fault reactivation was
likely more focused in zones of pre-existing tectonic weakness that were previously
affected by pre-ore alteration, creating structural traps that were open for fluid flow,
hydrothermal alteration, and uranium mineralization. Syn-ore Ms 2 muscovite has δ 18 O and
δ 2 H isotopic compositions typical of low latitude basinal brines (Fig. 4.11) similar to those
of unconformity-related U-deposits in the Athabasca (e.g. Fayek and Kyser, 1997; Cuney
and Kyser, 2008) and Kombolgie basins (e.g. Polito et al., 2004, 2006). The ore-forming
fluid most likely originated in the El Sherana Basin and descended downward into the
basement rocks along fracture systems created by brittle reactivation of the El Sherana-
Palette fault system (Fig. 4.15B). The mineralizing brine contained U, Au and PGE, the
former most likely leached from detrital U-bearing minerals (e.g. monazite and apatite) in
the El Sherana Basin sandstone, and the Au and PGE from alteration of felsic volcanics and
mafic rocks that comprised much of the El Sherana Group subsequent to burial and
diagenesis (Fig. 4.15B).
The syn-ore alteration is associated with precipitation of U 1 ±Au 1 mineralization in
faulted and brecciated contact between reducing carbonaceous and cherty ferruginous shale
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