CHARACTERIZING URANIUM OCCURRENCES AND DISTRIBUTION IN VIRGINIA

The tendency for uranium to concentrate in preferred rock types is clearly evident in the reported average “background” abundances in igneous, metamorphic and sedimentary rocks worldwide. In Virginia, the natural variability of uranium concentrations in rocks that tend to be enriched (i.e. high background) is poorly understood. This makes assessments of public health impacts related to natural environmental radioactivity difficult. Evaluating the geologic factors that have influenced uranium enrichment can help characterize this variability. This may also lead to the identification of important mineralization processes within broader metallogenic provinces with the potential for undiscovered energy fuel resources.

Notable occurrences of uranium-enriched rocks were compiled from published reports, unpublished geochemical data, and field scintillometer measurements. The criteria for selection included the documented presence of uranium-bearing minerals, the detection of elevated natural radioactivity, and geochemical data indicating elevated uranium content when compared to the expected natural background concentrations. To date, over 55 occurrences have been identified. Preliminary characterization of the lithotectonic framework of these occurrences highlights an affinity for uranium enrichment in seven geologic terrains in Virginia that include: (1) Tertiary-age marine phosphatic sedimentary rocks, (2) Late Jurassic-Early Cretaceous alkalic igneous rocks, (3) Triassic-Jurassic carbonaceous sedimentary strata and contact metamorphic aureoles, (4) late Paleozoic pegmatites and late magmatic stage granitic rocks, (5) Late Devonian and Early Mississippian black shales and sandstones, (6) Middle and Late Proterozoic alkali-rich plutonic rocks, and (7) major cataclasite/mylonite zones. Follow-up sampling and geochemical analysis is expected to further elucidate the metallogenic significance of these occurrences. It is hoped that the results will provide not only a better understanding of the natural variability of uranium in Virginia’s geological environment, but also a guide for the exploration of potentially undiscovered resources.