UBC Theses and Dissertations
Till geochemistry and lithogeochemical exploration for a concealed kimberlite, Northwest Territories, Canada Wickham, Andrew
Research at the Kelvin kimberlite, NWT, is helping to define surface exploration practices and is testing new host rock lithogeochemical exploration tools that will result in reduced costs and improved discovery success. In regions where recent glaciation has buried kimberlites under glacial sediments, surface geochemical detection methods are best interpreted when coupled with a comprehension of the landscape formation processes. The glacial, post-glacial, and cryoturbation processes that have affected the landscape have, in turn, affected the dispersal of geochemical signatures in the till that can be detected and exploited by detailed surface mapping, sampling, and geochemical analysis. The Kelvin kimberlite is an inclined pipe that subcrops from metaturbidite country-rock beneath a lake. No indicator mineral train has been detected at Kelvin by traditional indicator mineral methods. Relative uniformity of surficial material (<6m thick till blanket) allows for extensive B-horizon soil sampling above the kimberlite, up-ice, and up to 1 km down-ice. Four acid and aqua regia ICP-MS results of the -180 μm fraction indicate the presence of subtle pathfinder element trains originating from the kimberlite subcrop location and extending for >1km down-ice. Dry sonic sieving and four acid digestion results provide interpretations of geochemical partitioning and the ideal size fraction for geochemical sampling. Trace elements demonstrate systematically elevated concentrations in the fine and very fine silt fractions; however, background is higher and anomalous-to-background contrast is not enhanced compared to bulk -180 μm ratios. Elevated pathfinder concentrations in the fine to very fine sand fraction are attributed to fine kimberlite indicator minerals and their fragments, and display the best anomalous-to-background contrast. Additional research aims to detect mineralogical and metasomatic alteration signatures in the country-rock surrounding the Kelvin kimberlite in an attempted to develop exploration vectors. Hyperspectral scanning of drill core shows that the emplacement of the kimberlite did not produce pervasive mineralogical alteration of the surrounding country-rock. Evidence of alteration is limited to breccias and is vein-controlled, only extending a few meters from pipe contacts. Hyperspectral imaging and partial- and whole-rock lithogeochemical results do not detect evidence of pervasive alteration and preclude the identification of mineralogical or geochemical exploration vectors.
Item Citations and Data
Attribution-NonCommercial-NoDerivatives 4.0 International