| Summary: | Fission track analyses of minerals host rocks, and fission track mapping of uranium in samples from four Canadian Mississippi Valley type deposits, indicates that uranium concentrations in these samples are very minute (0.001 - 8.4 p.p.m.). The lowest values are found in the sulfides (galena 0.04 p.p.m., sphalerite 0.03 p.p.m., marcasite 0.06 p.p.m.), Sparry carbonates vary within three orders of magnitude (0.01 to 8.4 p.p.m.), while fluorite and pyrobitumen are very poor in uranium. The host rock dolostones contain generally more uranium than the ores (ca. 1.0 p.p.m.). Impurities within the host dolostones contain relatively higher concentrations (up to 5.56 p.p.m.). These results are unexpectedly low, in light of recently published values for sulfide minerals from other environments. Physio-chemical considerations would suggest that, if available, uranium should have precipitated in spatial association with the metallic sulfides. The extremely low values encountered suggest that the ore forming fluids did not have access to an appreciable supply of uranium. Economic concentrations of uranium in Mississippi Valley type deposits appear, therefore, unlikely. The coincidence of the numerous physical and chemical requirements for such a concentration might be met only in exceptional circumstances. Keywords: Pages: 95 Supervisor: Marcos Zentilli
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