Till Geochemistry and Lithogeochemical Exploration for a Concealed KimberliteTuesday, November 20, 2018 - 11:20 to 11:39 Theatre 1
Research at the Kelvin kimberlite, NWT is defining surface exploration practices and developing new exploration tools based on host rock lithogeochemical alteration, 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. Additionally, the application of geochemical and hyperspectral data to country rock alteration core can aid in the detection of kimberlites during near-miss drilling campaigns.
The Kelvin kimberlite is located eight kilometers from the Gahcho Kué diamond mine in the Northwest Territories. The inclined pipe sub-crops beneath a lake and dips into gneiss country rock towards the northwest with a surface projection of more than 600m long. Relative uniformity of surficial material (<6m thick till veneer) allows for extensive b-horizon soil sampling above the kimberlite, up-ice, and up to 1 km in the down-ice direction. Samples were sieved to -180 microns and analyzed by four acid digest ICP-MS and aqua-regia digest ICP-MS. Results indicate the soils to be very immature and identify the presence of a subtle Ni-Cr-Mg-Nb train originating from the lake side extending for >1km from source following the most recent ice direction to the west. The material for the train was abraded by the ice from the kimberlite, now sub-cropping beneath a lake, and would have provided additional support to drill what was initially targeted from geophysics.
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 accounting for country-rock lithology variation. Hyperspectral imaging of the same drill core will aim to detect and quantify secondary mineralogy and subtle changes in mineral composition that otherwise cannot be detected visually. This data will be used to generate mineralogical and chemical vectors beneficial in near-miss situations when drilling kimberlites and defining diatreme geometries.