SP44 Chapter 14: Till Geochemistry for Kimberlite Exploration
by L. Wilkinson, J.R. Harris, B. Kjarsgaard and M.B. McClenaghan.
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This chapter is from GAC's Special Paper 44: "GIS For the Earth Sciences" editted by Dr. Jeff Harris. To purchase the entire book in hardcopy or disc formats, please see the Special Papers section of our bookstore.
ABSTRACT: GIS visualization and analysis techniques were used to identify, and map, kimberlite exploration targets from till geochemical data, in the Lac de Gras area of Canada's Northwest Territories. Three surveys using different till size fractions allows for a comparison of kimberlite pathfinder elements Ba, Ce, Cr, La, Mg, and Ni, with respect to varying till size fraction. In addition, directional bias due to glacial dispersal in the various till size fractions is also assessed.
The best spatial structure in the various till datasets, assessed using geostatistical techniques (variograms) is observed in the local-scale Diavik clay+silt+sand survey data in a NESW direction, perpendicular to the dominant glacial transport direction. Similar patterns are observed in the regional till survey clay fraction data but not in the clay+silt fraction, suggesting the difference in behaviour may lie in surficial processes affecting the silt material.
Variogram analysis indicates no difference in anisotropy between samples from the areas of thick till and those obtained from areas of thinner till, consistent with the presence of a single till sheet having a similar glacial dispersal history. However, areas underlain by thicker till deposits are characterized by higher concentrations of kimberlite pathfinder elements Ba, Cr, and likely Mg, and Ni, for all till size fractions. This is likely related to differences in bedrock source material and transport distances. Identification of thresholds present in normal probability plots (i.e., based on thick versus thin till region) is used to identify and map geochemical anomalies for kimberlite exploration.
Geological Association of Canada
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