An overview of vis-nir-swir field spectroscopy - Spectral International

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UNCONFORMITY URANIUM DEPOSITS
Unconformity-associated uranium (U) deposits consist of pods, veins, and semimassive
replacements of uraninite which are overlain by zoned, quartz
dissolution, kaolinite, sudoite, illite, dravite, quartz alteration halos and located
near unconformities between Paleo- to Mesoproterozoic siliciclastic basins and
metamorphic basement.
In major producing basins (e.g. Athabasca, Kombolgie) the 1-2 km, flat-lying,
and apparently un-metamorphosed, mainly fluvial strata include red to pale tan
quartzose conglomerate, arenite and mudstone deposited from ~1730 to > Au, Pt, Cu, REE and Fe.
(Source: by C.W. Jefferson1, D.J. Thomas2, S.S. Gandhi1, P. Ramaekers3, G.
Delaney4, D. Brisbin2, C. Cutts5, P. Portella5, and R.A. Olson6: Mineral
Deposits of Canada, Unconformity Associated Uranium Deposits
http://gsc.nrcan.gc.ca/mindep/synth_dep/uranium/index_e.php)
The paleo-weathered basement immediately below the Athabasca Group has a
vertical profile ranging from a few centimeters up to 70 meters thick, with much
deeper pockets and slivers developed along fault zones. The following
description is after Macdonald (1980, 1985). The regolith is variably affected by
diagenetic iron reduction resulting in a bleached zone at the top, interpreted as
hematite removal from the upper "red zone" of the paleo-weathered basement
section. This bleached zone, always present immediately below the
unconformity, is composed of buff-colored clay and quartz. It crosscuts and
therefore post-dates the red zone beneath. Below this, the upper portion of the
regolith profile exhibits a strong red hematitic alteration that grades into
underlying greenish chloritic alteration. In profiles developed on the basement
meta-arkose, a white zone of white clay replacement of feldspars and mafic
minerals separates the red and green zones. A downward progression from this
kaolinite to illite and chlorite is common through the regolith profile.
Discussion continues regarding the respective contributions of paleo-weathering,
diagenesis and hydrothermal processes to the alteration preserved at the
unconformity. Cuney et al. (2003) stated that the regolith may represent a redox
front controlled by the degree of percolation of the oxidized diagenetic brines in
the basement, and that the lack of Ce-anomalies is not in favour of a lateritic
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