Investigation of Uranium Potential of Precambrian Metasedimentary Rocks, Central Laramie Range, Wyoming. Final Report

摘要

This study is directed toward evaluation of potential uraniferous quartz-pebble conglomerate occurrences or strata-bound uranium occurrences in the Laramie Range. Geologic investigations pursuant to that evaluation provide that metasediments in the central Laramie Range constitute an Archean greenstone belt which overlies remobilized granite-gneiss basement terrane of the Archean Wyoming Province. This greenstone belt is formed of branching arcuate, synformal keels of supracrustal rocks infolded and enveloped by granitic domes. The stratigraphic succession of the belt is a triad formed of lower mafic-ultramafic rocks including komatiites, middle mafic volcanics including pillow basalts, and an upper metasedimentary sequence composed of boulder paraconglomerates, graywackes, marbles, quartzites, pelites, thin quartz-pebble conglomerates and thin, banded iron formation. Because the metasedimentary sequence does not contain a thick, mature clastic wedge, a thick fluvial section, basal quartz-pebble conglomerates, or significant geochemical or radiometric anomalies and because the sequence is structurally complex and regionally of amphibolite facies metamorphic rank, the potential for uraniferous fossil placers is considered nil. Occurrences of other types may be indicated by radiometric and geochemical anomalies discovered over sheared zones within the granite-gneiss terrane and small radiometric anomalies over a coarse-grained phase of granite located north of the greenstone belt. (ERA citation 06:008634)