Distribution of Uranium in the crust of the northwestern canadian shield as shown by lake-sediment analysis

Abstract

In 1972 a reconnaissance geochemical survey was carried out by the Geological Survey of Canada in the northwestern Canadian Shield. Samples of nearshore lake sediment were collected, by helicopter, from 36,000 sq. miles of the Bear and Slave Structural Provinces. Sample density was one per 10 miles. These samples have since been analyzed for 27 elements. This paper is concerned with the distribution of uranium in 1,241 samples from the western third of the survey area. This region mainly comprises the Bear Province, of Proterozoic age.The Bear Province, which is a metallogenic province for uranium, also appears to be a geochemical province for this element. Uranium is four times more abundant in lake sediments from this area (5.3 p.p.m. U) as compared to the eastern part of the Slave Province (1.3 p.p.m. U). The lake-sediment data are in agreement with analyses of composite rock samples from two parts of the survey area.Within the Bear Province the regional distribution of uranium is controlled mainly by the distribution of Proterozoic granitic rocks. Nearly all areas of 5 p.p.m. U or greater in lake sediments are underlain by Proterozoic granites, or are near to these rocks. Within the granite areas, uranium is distributed along two sets of regularly spaced linear trends. The highest contents in lake sediment, which include values up to 300 p.p.m. U, commonly occur near the intersections of the two trends. These trends correspond to a set of northeast and a set of northwest strike-slip faults and lineaments that were produced by east-west compression of the Bear Province during and after the Hudsonian Orogeny (1750 m.y.). Outside the western margin of the survey area, complex epigenetic mineralization is associated with northeasterly-trending faults. Uranium has been produced from veins of this type at Port Radium and at the Rayrock Mine. Since it is associated with faults, this type of mineralization tends to occur in topographic depressions, that often contain lakes and swamps. Lake-sediment analysis is believed to be an excellent means of detecting such mineralization, both within the survey area and possibly elsewhere in the Canadian Shield. The data obtained during 1972 provide a basis for more detailed prospecting in the region.