Section 20
Chapter 19,036

Geological setting and genetic aspects of mineral occurrences in the southern Great Bear magmatic zone, Northwest Territories

Gandhi, S.S.

Bulletin - Geological Survey of Canada: 63-96


Accession: 019035636

The southern part of the Great Bear magmatic zone is characterized by abundant continental felsic volcanic rocks and related plutons, which were emplaced 1870-1840 Ma ago. The basement rocks include remnants of an early Proterozoic metamorphosed platform-shelf sequence and granitic plutons intrusive into the sequence. Mineral occurrences and deposits in the area are of six distinct metallogenic types. The argillaceous and silty beds of the Proterozoic metasedimetary sequence host synsedimentary/diagenetic sulphide and magnetite concentrations, some of which also served as favourable host rocks for later epigenetic mineralization. Occurrences genetically related to the Great Bear magmatic activity are of four types: felsic volcanic-associated uranium occurrences; monometallic and polymetallic iron oxide-rich veins and breccia-fillings exemplified by the magnetite-apatite-actinolite veins of Kiruna-type and the copper-uranium-gold-silver-rare-earth-bearing breccia zones of Olympic Dam-type; granite-related molybdenum-uranium + copper occurrences; and bismuth - cobalt - copper - gold-bearing hydrothermal arsenopyrite-pyrite veins and disseminations. The occurrences that postdate the Great Bear magmatic activity are the fracture-fillings and quartz veins containing pitchblende and copper sulphides, and include those in a giant quartz vein at the Rayrock mine that produced uranium in the 1950s. The most attractive targets from the standpoint of present exploration are the polymetallic Olympic Dam-type deposits. Evolution of the magmatic zone and the geological setting of the selected occurrences of each metallogenic type are described. Their genetic aspects are discussed and some comments on the resource potential and guides to exploration are provided.

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