Comparative petrochemistry of two cogenetic monzonitic laccoliths and genesis of associated uraniferous actinolite-apatite-magnetite veins, east arm of Great Slave Lake, District of Mackenzie

Two cogenetic mazonitic laccoliths, one hosting uraniferous actinolite-apatite-magnetite veins, were sampled for a comparative petrochemical study as an aid to understanding the genesis of the veins and to provide guides for exploration of other similar intrusions in the east arm of Great Slave Lake. The results reveal that the two bodies are very similar in chemical and mineralogical composition. They show a small compositional range and a calc-alkaline differentiation trend. They are subalkaline in character but locally show effects of alkali metasomatism. Uranium and thorium contents of both intrusions average about 6 and 27 ppm respectively. Most of the variation in the contents of uranium and thorium occurs at local rather than regional level in each of the laccoliths and the variance between the laccoliths is negligible. Although the range and mean of uranium values in both laccoliths are similar, the laccolith barren of veins has the values showing a clustered distribution within the range in contrast to the laccolith hosting the veins, which shows a scattered distribution suggesting some uranium mobility