Research at the Kelvin kimberlite, NWT, is defining surface exploration practices and 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 ratio. Whole soil commercial Pb isotope analysis of select soils provide supplemental data to fingerprint the petrogenetic source of anomalous samples.
Additional research is being carried out to detect alteration signatures in the country rock induced by the emplacement of the kimberlite. Lithogeochemical data from four drill holes aims to identify and quantify the metasomatic enrichment and depletion of elements sourced from the kimberlite, while hyperspectral imaging will aim to detect secondary mineralogy and subtle changes in mineral composition. This data will be used to generate mineralogical and geochemical vectors beneficial in near-miss situations when drilling kimberlites and defining diatreme geometries.