PRELIMINARY GEOCHEMICAL INVESTIGATIONS OF RARE EARTH ELEMENTS IN COAL-BEARING STRATA OF ALBERTA

Coal and coal byproducts are of considerable research interest worldwide as potential sources of rare earth elements (REEs), and researchers have already begun to demonstrate their prospectivity in several regions. Shales and claystones have also generated research interest as potential sources of REEs and are often associated and interbedded with coals. These strata tend to be discarded in coarse reject piles during mining, and therefore this waste stream could also be a potentially important source of REEs.

There are various possible mechanisms by which REEs may become enriched in coal, and the impact and relative significance of these mechanisms are dependent on regional and local factors such as geological setting, depositional history, metamorphism, and diagenesis. Thus, the sources and host phases of REEs associated with coals can vary significantly by geospatial location and geological time interval. In addition, REE content in coal mine waste depends on feed coal composition, processing, and storage conditions, with the consequence that REE anomalies and occurrences can vary by region and by mine.

Alberta has an estimated 2000 Gt of ultimate in-place coal reserves, primarily in Upper Jurassic, Cretaceous, and Lower Tertiary strata (AER ST31), and produced a cumulative 13.1 Mt of marketable subbituminous, metallurgical bituminous, and thermal bituminous coal in 2022 (AER ST98). However, the currently available data on REE content of coal deposits and waste streams in the province is limited, and location-specific data collection is required to understand the extent and potential of these resources in Alberta.

This study involved sampling and geochemical analyses of coal seams and related fine-grained sedimentary strata throughout the province. Approximately 40 drill cores representative of multiple localities and stratigraphic intervals were analyzed using portable X-ray fluorescence (n=16,222) and total REE abundances were inferred from proxy elements and partial REE suites. Lateral and vertical trends, anomalies, and correlations within the data were used to: (1) make preliminary interpretations of REE enrichment modes and phase associations in coal seams and related sedimentary units within a stratigraphic context, and (2) characterize the relative potential of different localities and intervals.