Abstract
In 1980, the Bureau of Mines and the Bureau of Land Management made a mineral reconnaissance in the Selawik Hills area of northwestern Alaska. The Selawik Hills are partially underlain by three Cretaceous alkaline complexes that have given rise to uranium and thorium mineral occurrences locally associated with columbium, fluorite, and rare-earth elements. Anomalous uranium occurs in altered zones in syenite that contains xenotime, zircon, fluorite, thorianite, and an unidentified columbium-uranium-titanium mineral found by microprobe examination; quartz vein systems associated with altered tectonic lineaments; and slightly uraniferous lamprophyre dikes. A low-grade occurrence of uranium in carbonaceous sandstone also was found within Tertiary coal-bearing sediments. Multiple thin seams of lignitic coal exposed in two outcroppings indicate that the sedimentary basin north of the Selawik Hills contains coal deposits of unknown extent. The uranium and thorium occurrences in igneous rock and the uranium at the adjacent sedimentary series both warrant further investigation. Detailed sampling, mapping, and geophysics followed by core drilling would be needed to estimate the economic significance of these occurrences.
