Northwest Territories Geological Survey

It took several decades to develop the necessary understanding of glaciation, geochemistry and mineralogy to refine exploration strategies and find the first kimberlite in the Northwest Territories, Canada. These fundamental drift prospecting strategies followed by geophysics and drilling have been used to locate many kimberlite occurrences over the years. Indicator minerals in surface sediments are still the primary datasets used to identify kimberlite exploration targets; however, many of the kimberlite sources for the well-defined indicator mineral dispersals have been identified. Exploration must now focus on regions with more complex surficial geology where primary dispersal patterns in till are obscured by post-depositional modification. These patterns are largely defined using data from historical ‘till’ surveys that often failed to properly scrutinize the sample media; reworked tills and other surficial materials were commonly collected. The regional surficial geology maps (e.g. 1:50,000 to 1:250,000) typically published by geological surveys to stimulate reconnaissance exploration in new areas are generally incapable of providing sufficient resolution to determine the genesis and post-glacial alteration of sample media or reconcile complex dispersal patterns. Furthermore, advances in analytical methods have yielded compiled datasets with results from multiple methods that are not always comparable. Without a new, more detailed and systematic approach to evaluating surface sediment data, exploration in areas with complex glacial, deglacial and post-glacial histories will be challenged to discover kimberlite.

The accessibility, quality and variety of high-resolution aerial or satellite imagery and topographic data has improved significantly over the years, affording a more detailed interpretation of the surficial environment. These detailed interpretations have allowed us to evaluate historical data with a new perspective and target the collection of new, high-quality data. Throughout the Slave Province, we have tailored surficial interpretations to distinguish in-situ till from reworked till and other materials, which have altered dispersion and indicator mineral concentrations. Using examples from the Lac de Gras area, this presentation demonstrates how a detailed surficial framework, combined with an understanding of the varied analytical methods, is applied to historical datasets to refine indicator dispersal patterns and identify new exploration targets. By standardizing the data based on sediment genesis and transport mechanisms, the dataset becomes more suitable for statistical evaluation and anomaly threshold determinations that are unique to specific data subpopulations. As a result, anomaly contrasts are improved, and complex dispersals can be unravelled. In addition, areas with insufficient data coverage are identified and the necessary framework to complete informed, efficient infill or new sampling is provided. The examples we share highlight that there is no replacement for project-scale understanding of surficial geology and its varied effects on mineral dispersals in the development and interpretation of a surface sediment dataset used to identify kimberlite exploration targets.