A GLOBAL ASSESSMENT OF REE’S IN SEDIMENTARY PHOSPHATE DEPOSITS
Published values for known horizons and/or published values for equivalent-age horizons, combined with the supposition that REE concentrations in francolite from specific phosphate horizons are relatively consistent, can be used to approximate REE grades and tonnages of currently mined phosphorites. These speculative estimates provide approximations of REE flux through mining, beneficiation, and dissolution operations associated with ongoing phosphate fertilizer production.
Moreover, recognition that the tonnages and HREE concentrations of some unmined phosphorite deposits dwarf the world’s richest REE deposits suggests that these deposits might constitute standalone REE deposits. Documented global-secular REE abundance variations identify phosphorite occurrences deposited during periods that were favorable for deposition of high-REE containing strata. The hypothesized genesis of these REE-rich occurrences strongly supports the long-debated suggestion that oceanic REE contents vary in a secular fashion and that associated high-grade REE abundances reflect oceanic redox state transitions during specific time periods. This new process-based model, based on observed variations in global-secular REE abundances, identifies phosphorite horizons deposited during periods favourable for high-grade REE accumulation.