From introduction: This report presents data gathered in a Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) conducted by the Los Alamos Scientific Laboratory (LASL) in southwestern Montana. The HSSR was initiated by the US Department of Energy (DOE) to outline areas favorable for uranium exploration by examining uranium concentrations in natural waters and stream sediments.
From 1995 sites in the San Juan Mountains area, 1706 water and 1982 sediment samples were collected during June-July 1976 and analyzed for uranium. The area includes the southern third of the Colorado mineral belt which has yielded rich ores of gold, silver, copper, lead, zinc, and molybdenum. The broadly domed mountains are capped by 2500 m of Tertiary volcanics, deeply eroded to expose a Precambrian crystalline core. Adjacent plateaus underlain by Mesozoic sedimentary rocks were included in the reconnaissance. Average value of uranium in water samples from mountains was less than 0.5 parts per billion, from plateaus was 1-2 parts per billion, from Mancos shale areas exceeded 2 parts per billion. Anomalous sediment samples, 40 ppm uranium, came from near Storm King Mountain and upper Vallecito Creek. Other anomalous areas, including the Lake City mining district, were well defined by 4-30 parts per million uranium in sediment and 3-30 parts per billion uranium in water. Anomalous areas not previously reported indicate favorable areas for future exploration.