The progress in the study of REE-rich deep-sea sediments

The deep-sea sediments rich in rare earth elements discovered in recent years in the Pacific and Indian Ocean basin are a potential rare earth mineral resource. The metalliferous sediments, zeolite clay and pelagic clay are thought to be the main types of REY-rich sediments with high total REY(REE+Y) content (400×10^-6-2000×10^-6, the highest up to 6600×10^-6) and heavy rare earth content (HREE). The HREE values of the sediments are nearly twice as abundant as those in the southern Chinaion-absorption-type deposits. Previous chemical and mineral studies suggest that Fe/Mn oxide and oxyhydroxide precipitated from hydrothermal activities is the main host of the REY in the metalliferous sediments, while phosphate whose chemical composition is equivalent to apatite (such as fish debris) is the main carrier of rare earth elements in the zeolite clay and pelagic clay. The NASC-normalized REE patterns of deep-sea sediments are similar to those of seawater, indicating that the rare earth elements of the sediments were taken up from ambient seawater. REY were mainly enriched at the early diagenetic stage of apatite without differentiation. Many achievements have been made about the rare earth elements in deep-sea sediments in recent years. However, the enrichment mechanisms of rare earth elements in deep-sea sediments and influencing factors still need further study. China has been the dominant producer of REE and hosts the most known global reserves. In order to safeguard China's right in the competition for REE in the international seabed and safeguard China's benefit, it is very necessary and critical to search for and evaluate potential marine REE resources.