Uraninite-Bearing Deposits, Charlebois Lake Area, Northeastern Saskatchewan

CIM Bulletin, 1952

J. B. Mawdsley

The uraninite-bearing deposits in the Charlebois Lake area of northeastern Saskatchewan are unusual and important concentrations of uranium. They were first discovered in 1949 and preliminary development work to the end of the 1951 field season indicates the probability that this will become another uranium producing di strict. The deposits are in zones bordering granite masses. These zones are of migmatite (mixed rocks ) composed of calcium-1ich meta-sediments intruded and replaced by a fine-grained white pegmatite. Locally this pegmatite is replaced by an end fraction which is relatively rich in fine-grained disseminated uraninite; it is these occurrences that constitute the bodies of economic inter- est. The fine-grained white pegmatirte contains plagioclase feldspar more lime-rich than t hat in the granites of which it is an end differentiate. This extra lime, evidently derived from the intruded Sediments, would result in the raising of the temperature of crystallization of t he pegmatite- forming magma, thus consolidating it rapidly near the granite contacts as a fine-grained pegmatite. The end liquor containing uranium was evidently locally concentrated in minor fracture zones in these pegmatites. Where no lime sediments were present. the coarse-grained alkaline pegmatites were formed. Their crystallization would not be accelerated and the uranium would tend not to be localized in the pegmatite but to migrate and consolidate at lower temperatures with the end products, possibly in some instances as pitchblende veins.
Keywords: Biotite, biotite, feldspar, granite, pegmatite, Uraninite, Feldspars, Fines, Granite, Granites, Pegmatite, Pegmatites, quartz, Rock, Rocks