Uranium hydrogeochemical and stream sediment reconnaissance of the Denver and Greeley NTMS Quadrangles, Colorado

Abstract

Although this report covers two National Topographic Map Series 2/sup 0/ quadrangles, the data for each quadrangle are presented separately. Evaluation of the data by quadrangle resulted in the delineation of areas in which water and/or sediment uranium concentrations are notably higher than surrounding background concentrations. The major clusters of anomalous water samples were found in areas of the Denver Basin underlain by the Pierre, Laramie, Fox Hills, Denver, and Arapahoe formations. Most of the anomalous sediment samples were collected in areas of the Front Range underlain by Precambrian crystalline rocks, particularly granites of the Silver Plume-Sherman group. Many of the anomalous sediment samples are from sites located near fault zones. The data in this report are also presented by geologic/physiographic province because background uranium concentrations in Front Range samples differ significantly from those in the Denver Basin. Denver Basin waters have higher mean uranium concentrations (mean 14.4 ppB) than Front Range waters (mean 3.3 ppB). Conversely, Front Range sediments are more uraniferous (mean 14.7 ppM) than those in the Denver Basin (mean 6.1 ppM). These differences in background uranium concentrations between Front Range and Denver Basin samples can be attributed to differences in regional geology, physiography, and (in the case of water) the ratio of surface water to ground water sites sampled. There is a significant northward increase in uranium concentrations in water samples from the Denver Basin. The higher uranium concentrations in water samples from the northern part of the basin are probably due to leaching of uraniferous strata in the Pierre and Laramie formations which crop out in that area.