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Lithostratigraphy and Geochemistry of the High-Grade Metasedimentary Rocks in the Thompson Nickel Belt and Adjacent Kisseynew Domain, Manitoba: Implications for Nickel Exploration^*

H. V. Zwanzig, J. J. Macek and C. R. McGregor

Manitoba Science, Technology, Energy and Mines, Manitoba Geological Survey, 360–1395 Ellice Avenue, Winnipeg, Manitoba R3G 3P2, Canada

Corresponding author: e-mail: herman.zwanzig{at}gov.mb.ca

Exploration for nickel in the Thompson nickel belt is focused on specific paragneiss units within the Paleoproterozoic sedimentary and volcanic cover succession (Ospwagan Group) on the northwestern margin of the Archean Superior craton. These units host ultramafic bodies and all significant nickel deposits in the Thompson nickel belt. Knowledge of the lithostratigraphy is therefore essential for finding the units with the highest potential for the discovery of new nickel deposits. This is made practical by a distinctive stratigraphic succession with numerous marker units, including metamorphosed quartzite, carbonate, pelite, iron formation, and graywacke, as summarized in this paper. However, the sedimentary rocks are generally highly deformed and metamorphosed, making the recognition of some units difficult and their sedimentary origin obscure.

To better recognize the sedimentary protoliths of orehosting and related units, a simple plot of SiO₂ versus Al₂O₃ is used to estimate the approximate proportions of siliciclastic and chemical sedimentary components. This demonstrates that much of the succession, which was previously considered to be derived from calcareous and ferruginous chemical sediments, is a hybrid containing a substantial siliciclastic component, thus explaining the present mineralogy and geochemistry and assisting in the recognition of units at various metamorphic grades.

Extended-element plots, using the most abundant metapelite unit in the Ospwagan Group as the normalizing factor, show a common provenance for the entire group. They also illustrate a clear difference between the Ospwagan Group and the underlying basements gneiss and allow the Ospwagan Group to be distinguished from petrographically similar but economically barren, younger paragneiss units of the Burntwood and Grass River groups. Unlike the Ospwagan Group, the younger units, which predominate in the Kisseynew Domain adjoining the Thompson nickel belt, were derived mainly from an exotic Paleoproterozoic arc-related source and therefore have a different geochemical signature. This geochemical difference can be utilized in areas of sparse geologic information, such as beneath Phanerozoic or glacial cover, where initial exploration drilling tests new geophysical targets.

Combined litho- and chemostratigraphy improve insight into basin evolution, which probably occurred on a ca. 2 Ga passive continental margin or shelf. The ca. 1880 Ma maficultramafic magmatism related to the nickel deposits may have formed in a different tectonic environment, possibly in a continental back arc associated with a recently proposed episode of felsic calc-alkaline plutonism.

This article has been cited by other articles:

				C. O. Boehm, C. O. Bohm, H. V. Zwanzig, and R. A. Creaser Sm-Nd Isotope Technique as An Exploration Tool: Delineating the Northern Extension of the Thompson Nickel Belt, Manitoba, Canada Economic Geology, November 1, 2007; 102(7): 1217 - 1231. [Abstract] [Full Text] [PDF]