Uranium hydrogeochemical and stream sediment reconnaissance in Lincoln and Flathead Counties, northwest Montana
Description: Between mid-May and late June 1976, 3409 water and water-transported sediment samples were collected from 1781 locations spread over an approximate 17000-km/sup 2/ area of northwestern Montana. All of the samples were analyzed for total uranium at the LASL, using standardized procedures and rigorous quality controls, the waters by fluorometry and the sediment (and those waters with greater than 10 ppb uranium) by delayed-neutron counting methods. All of the field collection, treatment, and packaging of the samples was performed following strict LASL specifications. The uranium concentrations measured in the waters range from undetectable (less than 0.2) ppb to 173.6 ppb, but average only 0.66 ppb. The low uranium concentrations in the waters of this area are thought to be due primarily to a general lack of readily soluble uranium and dilution with spring runoff. Those locations which did have abnormally high uranium were examined more closely, and follow-up field examinations are recommended in the vicinity of some of these sites. The uranium content of the sediment samples range from 0.5 ppM to 52.2 ppM and average 4.56 ppM. Sample locations with high and/or anomalous uranium values were examined with respect to the local geology, water chemistry, and other relevant factors. A distinct correlation between the high uranium in sediment and epithermal and mesothermal veins associated with nearby faults and folds is evident at several locations. Areas believed to be favorable for follow-up field investigations based on the sediment data are indicated. A correlation between high uranium in water and high uranium in sediment is evident at only a single location. The generally low uranium concentrations in water and moderate concentrations in sediment seem to indicate that most of the uranium that does exist in this area is bound up in resistant minerals.
Date: May 1, 1977
Creator: Aamodt, P. L.