Over 100 samples of ‘pegmatite’ and associated host rocks from the Cree Lake Zone of northern Saskatchewan have been studied. The degree of U and Th enrichment of the pegmatites appears to depend on the parent material of the anatectic melts produced during the Hudsonian thermotectonic event. Evidence for Archaean granulite-facies depletion of U and Th is inconclusive; however, important enrichment of U and Th in the basal Aphebian is associated with metamorphosed black shales and possibly evaporates.