Geochemistry of rare earth elements in bottom sediments of the Brazil Basin, Atlantic Ocean

The sedimentation and ore formation were studied in sediments from nine stations located in the 24°W profile in the Brazil Basin of the Atlantic Ocean. The sediments are represented by mio- and hemipelagic muds, which are variably enriched in hydrothermal iron and manganese oxyhydroxides. As compared to the sediments from other basins of the Atlantic Ocean, these rocks are marked by extremely high manganese contents (up to 1.33%) and maximal enrichment in Ce. It was shown that the positive Ce anomaly is related to the REE accumulation on iron oxyhydroxides. Influence of hydrothermal source leads to the decrease of Ce anomaly and LREE/HREE ratio. In the reduced sediments, preservation of positive Ce anomaly and/or its disappearance was observed after iron and manganese reduction. The REE contents were determined for the first time in the Ethmodiscus oozes of the Brazil Basin. Ore deposits of the Brazil Basin are represented by ferromanganese crust and ferromanganese nodules. Judging from the contents of iron, manganese, rare, and trace elements, these formations are ascribed to the sedimentation (hydrogenic) deposits. They are characterized by a notable positive Ce anomaly in the REE pattern. The extremely high Ce content (up to 96% of total REE) was discovered for the first time in the buried nodules (Mn/Fe = 0.88).