Rare earths in sediments

Abstract

The relative elemental abundances of the rare-earth elements (REE) in a composite of 40 North American shales and in the average for 38 individual sediment samples are found to be identical with each other and with the average determined for sediments of the Russian Platform, to within an experimental uncertainty of ±10% (standard deviation). The average RE distributions for 9 carbonates, 7 sandstones, 5 graywackes, and 8 ocean sediments are identical with the North American shale distribution to within a standard deviation of ±15%, and the average for 9 shales lacks only one element of being so. Only 14 of the 38 individual sediment distributions are identical with the North American shale composite to within ±15%, but fewer than 3% of the distributions differ in any part by a factor of 2 and fewer than 15% of them differ by a factor of 1.5. The spread in absolute RE content for sediments of a given type ranges from a factor of less than 3 for the ocean sediments to more than 30 for the sandstones. The average absolute RE contents increase in the order limestone, sandstone, graywacke, ocean sediment, shale. The absolute RE contents of the shale composites vary from somewhat more than 75 ppm to 335 ppm. The average total RE content of sediments is probably between 150 and 300 ppm. Preliminary results for separated minerals indicate that the bulk of the REE in the St. Peter sandstone is in the quartz, and in the Byron formation limestone it is in the carbonate. Experiments on adsorption of the REE on calcite are described.