Composition of phosphorites from the ocean floor and ocean islands

Rhenium contents were determined in 12 samples of oceanic phosphorites using kinetic and ICP-MS techniques, the latter of which appeared to be more correct. Rhenium contents in phosphorites from the ocean floor varied from 3 to 50 ppb, whereas that in phosphorites from the Christmas and Nauru islands are 1.3 and less <1 ppb, respectively and are similar to average rhenium content in sedimentary rocks (about 1 ppb). Rhenium does not show any relationship with phosphorus, aluminosilicates, or iron and manganese oxyhydroxides, but a correlation trend with organic carbon and total sulfur (partially bound in pyrite) is revealed. Enclosing reduced biogenic sediments enriched in hydrogenic rhenium serve as a primary rhenium source for phosphorites. Rhenium concentration in phosphorites possibly depends on duration of their presence in reduced environment and on conditions of their subsequent exposure on the ocean floor.