Regional Structure of the Thompson-Moak Lake Nickel Belt

CIM Bulletin, 1961


. The Thompson-Moak Lake nickel belt lies along the root of a Precambrian mountain range of the islandarc or alpine type. This range coincides with the boundary between the Superior and Churchill blocks of the Canadian Precambrian shield. The nickeliferous peridotites and nickel ores occur along a negative gravity strip, which also coincides with strong thrust faulting and the axis of greatest deformation of the mountain range. Similar structures and highly nickeliferous peridotites occur in present-day island arcs. Much of the belt is covered by Paleozoic rocks, but a length of 270 miles may be explored by presentday methods. Nickel deposits have been located along 60 miles of the belt. The length of the favorable structure and the size of the known deposits suggest that this will be one of the world's major nickel regions. The regional gravity anomalies, which consist of a branching negative strip bordered by two positive strips are best explained by major warps of a crust consisting of a granitic and basaltic layer. The ore deposits occur in serpentinized peridotite or in gneiss near peridotite. The sulphide mineralogy is similar to that of the Sudbury ores, but the structure of the ore in gneiss is different, and the Manitoba ores are almost entirely nickel. The mineralogy of the silicate gangue in the gneiss1c ore is typical of the almandine- amphibolite facies, sillimanitealmandine subfacies. Possible igneous and metamorphic origins are considered as a guide to further research on the problem of genesis.
Keywords: gneiss, gravity anomalies, island arc, Nelson River, peridotites, Gravity, Manitoba, Ore, Ores, Rocks, Structure, sulphide, Sulphides