National Uranium Resource Evaluation: Sandpoint Quadrangle, Washington, Idaho, and Montana

The Sandpoint Quadrangle, Washington, Idaho, and Montana, was evaluated to identify and delineate areas favorable for uranium deposits in accordance with criteria developed for the National Uranium Resource Evaluation. Surface radiometric reconnaissance, geochemical sampling, and reconnaissance airborne radiometric surveying were used for overall evaluation of the quadrangle. Detailed airborne radiometric surveying, geologic mapping, and other types of surface studies were used in suspected favorable areas. Results of the work indicate favorability for Wyoming roll-front type uranium deposits in conglomerates and sandstones of the Tertiary O'Brien Creek and Tiger Formations. Synorogenic plutonic rocks are considered favorable in some areas for authigenic or anatectic deposits, and radioactive postorogenic plutons are favorable for magnetic-hydrothermal deposits. Small areas containing sulfide-bearing metamorphic rocks adjacent to radioactive plutons are favorable for allogenic deposits similar to those at the Midnite Mine 10km southwest of the quadrangle. Uraniferous conglomerates of possible Tertiary age in the southwest corner of the quadrangle may be favorable for sandstone-type uranium deposits. In the Cambrian Metaline Formation, the Josephine Breccia, contains local uranium concentrations and may be favorable for unclassified-type deposits. The overlying Ordovician Ledbetter Slate also contains uranium occurrences and might contain syngenetic or hydrothermal deposits. Although thorium-rich veins in Precambrian Belt Supergroup metasedimentary rocks in Idaho contain much less uranium than thorium, they may be favorable for polymetallic vein-type uranium deposits. Late Paleozoic and Mesozoic metasedimentary and metavolcanic rocks, nonradioactive plutonic rocks, Tertiary volcanic rocks, and Quaternary deposits are considered unfavorable for uranium deposits