Rare-Earth Elements and Noble Metals in Phosphorites of the Gremuchy Occurrence, Lesser Khingan, Far East of Russia

Numerous phosphorite occurrences are located among the Riphean–Early Cambrian rocks of the Khingan Group (Lessr Khingan, JAO). They are associated spatially and genetically with uranium, iron, and manganese ore occurrences. The phosphorites of the Gremuchy occurrence are enriched in rare-earth elements (REE) and yttrium (up to 813.58 g/t), uranium (up to 52.23 g/t), and gold (up to 17.03 g/t), and can be considered as a complex of phosphorus–uranium–gold–rare-earth ores. REE-rich fluorapatite is the main concentrator of phosphorus in these rocks. REE do not form their own minerals, while gold, silver, and platinum are found as microinclusions. The concentrations of phosphorus, radioactive, and rare-earth elements are positively correlated with the organic carbon content, which supports their coprecipitation from seawater enriched in rare and rare-earth elements supplied by hydrothermal vents on the surface of the slope of seamount volcanoes.