RECOVERY FROM THE EARLY TRIASSIC HOTHOUSE LED TO REGIONAL FORMATION OF RARE EARTH ELEMENT ENRICHED PHOSPHORITES (Invited Presentation)

Rare Earth Element (REE) potential of sedimentary rocks in the Sverdrup Basin, Canadian Arctic Archipelago, were examined. Over 870 mudstone samples were analysed to form a composite profile through a large part of the sedimentary column - from Carboniferous through to Late Triassic strata, as well as Cretaceous strata. The Jurassic portion of the basin has incomplete sample coverage. Throughout the sampled intervals, SREE values show minor variability (21.3 to 557 ppm, mean 157 ± 48 ppm), indicating that REEs are generally not enriched throughout most of the depositional history. One anomaly is the Middle Triassic Murray Harbour Formation, an organic-rich black shale characterised by abundant phosphate nodules. Phosphate nodules are highly enriched in REEs (417 to 3260 ppm, 1290 ± 622 ppm). Such sedimentary phosphorite deposits are a particularly appealing source of REEs as they are nearly 100% recoverable during phosphate extraction.

The Murray Harbour Formation was deposited during final cooling following the Early Triassic hothouse, in response to a rising thermocline and renewed nutrient upwelling. This global event was expressed across NW Pangea as deposition of organic rich phosphatic black shales. Phosphatic units temporally equivalent to the Murray Harbour Formation include the Doig Phosphate zone in the Western Canada Sedimentary Basin, the Shublik Formation of northern Alaska, and Botnehia Formation of Spitsbergen. Similar REE enriched units may be widespread.