CONSTRAINING DEPOSITION AND DIAGENESIS OF SEDIMENTARY PHOSPHORITE DEPOSITS OF WESTERN CANADA TO EVALUATE THEIR POTENTIAL AS AN ECONOMICAL SOURCE OF REES

Elevated concentrations of rare earth elements (REEs) in phosphorites have sparked interest in these rocks as a potential source of REEs through extraction as a by-product of phosphate mining. Highly heavy REE (HREE) enriched phosphorite formations within North America may be able to meet 100% of global HREE demand. Importantly, understanding the processes by which REEs become enriched in these rocks is vital for efforts to pinpoint the highest-grade deposits, but these remain incompletely constrained. Specifically, REE enrichments in phosphorites have alternately been attributed to diagenetic alteration and temporal changes in ocean chemistry. Here, we evaluate the relative roles of these enrichment processes through a focused study of phosphorite occurrences in the Early Triassic Doig Formation and Early Jurassic Fernie Formation within the Western Canada Sedimentary Basin, where previous studies have documented high concentrations of La, Ce, and Y. Samples from both formations were collected from remarkably well exposed outcrops at Williston Lake in northeastern British Columbia. The phosphorites occur as phosphate nodules in the Doig Formation and granular phosphorites in the Fernie Formation, consistent with the different formation environments that have been proposed. These contrasting modes of formation present an opportunity to investigate the effect of palaeoenvironmental conditions on phosphorite REE contents and will hence aid in the development of exploration models. The Fernie Formation phosphorites in particular have been associated with euxinic to anoxic conditions during the End-Triassic Extinction, allowing us to evaluate the role of ocean anoxia in governing REE incorporation in phosphorites. Our ongoing efforts will allow us to characterize the REE contents and ratios and O isotopic compositions of these Triassic-Early Jurassic phosphorites. In turn, these efforts will allow us to explore the impacts of depositional environment, palaeoenvironmental conditions, and diagenetic history on the REE potential of phosphorites, and ultimately yield revised exploration models for REE extraction from these sedimentary deposits.