Non-traditional sources of critical minerals from the Western Canada Sedimentary Basin

Abstract

The material demands of the energy transition will be immense, requiring new sources of critical metals required in clean energy technologies. Among the most important of these are the rare earth elements (REE) and lithium (Li). The REE, which include the lanthanide elements and yttrium (Y), are currently produced from peralkaline igneous complexes, carbonatites, or ion-adsorption clay deposits and are prized for their unique chemical, magnetic, and catalytic properties. Their primary importance in the energy transition is their necessity in permanent magnets for wind turbines and electric vehicles. Conversely, Li is the lightest metal on the periodic table and is currently produced from pegmatites and continental brine deposits. It has the highest energy density among all metals and is therefore crucial in electric vehicle and grid storage batteries and is projected to have the largest increase in demand among all critical metals. Meeting the demand for these metals can be difficult since REE and Li ore deposits are rare and unevenly distributed globally which can lead to domestic supply concerns, exploration can be difficult, and production can be expensive and fraught with numerous environmental, social, and governance (ESG) concerns. In light of these factors, new sources of these metals are gaining prominence including waste from industrial processes and those from previously overlooked geological environments. This research seeks to increase the understanding and assess the resource potential of critical minerals from non-traditional sources of the Western Canada Sedimentary Basin (WCSB) with a focus on REE from coal combustion by-products (CCBs) and Li from basinal brines. The first phase of this work used machine learning to identify geochemical indicators of REE enrichment in sedimentary strata which can be used to predict where elevated abundances may be found and to inform supplementary sampling programs. It was found that REE were most associated with Th, Nb, and P and enriched in fine-grained clastic lithologies (i.e. shales and mudstones). As a result, the effects of clay minerals on REE transport and deposition were then studied via geochemical modelling and synchrotron x-ray absorption spectroscopy (XAS). Next, the REE potential of Alberta and Saskatchewan CCBs were assessed through geochemical, machine learning, and XAS methods. REE concentrations were comparable to those of other CCBs globally while similar geochemical relationships were identified as in the machine learning study. Leaching experiments and sequential extractions indicated that REE in the Ca-rich Poplar River ashes were most easily leached into solution, while XAS analyses found the REE were hosted in silicate and phosphate mineral phases that were transferred from the coals to the CCBs during combustion. The third phase studied the critical metal potential of WCSB basinal brines. While REE do not occur in economic abundances, Li concentrations across the basin can regularly exceed the economic threshold (~75 mg/L). However, the source of Li is poorly understood. Based on an increasing body of evidence, in-situ water-rock interactions are proposed to be the major process supplying Li to the brines. These findings can be incorporated into a broader deposit model which can aid exploration across the basin. This work is an important step in realizing the vast mineral potential that may occur in previously underexplored sources from the WCSB which can play a crucial role in providing the raw materials necessary for the transition away from carbon-intensive energy systems and mitigating future anthropogenic climate driven changes to the Earth system while providing new economic and employment opportunities.