Uranium and thorium in the Precambrian basement of western Canada. I. Abundance and distribution

Delayed neutron activation analyses of 182 core samples from the basement of the western Canada sedimentary basin give mean values of 4.13 ppm U and 21.1 ppm Th. These values are almost twice the published values for the Shield as a whole. Replicate analyses of a composite sample of all cores indicates an analytical precision of ±1% for uranium and ±7% for thorium.Histograms of number of samples vs. U and Th values indicate a negatively skewed frequency distribution. Analysis of composite samples prepared from a large number of hand specimens may tend to conceal this skewed nature. Mean abundance values will also be influenced by the form of the U and Th frequency distributions.Trend surface analysis, with smoothing to reduce the effect of high or low single sample values, indicates two 'highs' common to both U and Th. The helium-producing area around Swift Current, Saskatchewan is associated with a high U–Th plutonic complex. A linear belt trending northeast from Edmonton appears to be a Hudsonian metamorphic belt in which U and Th have been concentrated. Several local concentrations of U or Th are found in the Peace River Arch of northern Alberta.