A ‘CRITICAL MINERAL INDEX’: GEOCHEMICAL SIGNAL OF CARBONATITE-RELATED CRITICAL METALS IN PROVINCIAL DRAINAGE SEDIMENTS

Consisting of at least 30% primary carbonate minerals, carbonatites are rare igneous rocks that have become increasingly important exploration targets, because they are major sources of Nb, rare earth elements (REE), and other critical minerals. Demand for these minerals has rapidly increased as the world transitions to low-carbon technologies. The British Columbia alkaline province, which defines a long (at least 1000 km), narrow (ca. 200 km) orogen-parallel belt along the western flank of Ancestral North America, contains numerous carbonatites and related silica-undersaturated and alkaline silicate rocks that host REE and rare-metal resources. Using multi-element stream-sediment geochemical data collected as part of Regional Geochemical Survey (RGS) programs since 1976, we define a multivariate ‘critical mineral index’ to assess prospectivity for carbonatite-hosted critical metals. Based on discriminant analysis of a training sub-set of the data downstream of known carbonatite occurrences (n=26), our carbonatite index, which is validated by a test sub-set of the data (n=27), highlights numerous areas prospective for REE in the alkaline province. Stream-sediment data showing carbonatite index scores greater than the 93rd percentile (n = 50) reveal maximum contrast of REE, Nb, Ta, Ti, Zr, Hf, Th, U, P, K and other carbonatite indicators relative to the median (background) concentrations in stream sediments of the study area. Estimated predicted geochemical resources (in tonnes of metal per 1 m depth), based on productivities of metals in the stream basins, suggest significant potential for REE and other carbonatite-hosted critical metals. Based on data from known carbonatites, we propose a refined prospectivity approach to assess the critical metals potential of underexplored regions that includes detailed stream-sediment, panned heavy mineral concentrate, and soil lithochemical surveys and high-resolution airborne radiometric and magnetic data.