Research and drilling by Japan’s Agency for Marine-Earth Science and Technology claims to have found deposits of rare earth minerals in deep sea muds in the Pacific, much of it in international waters surrounding Hawaii.
According to Reuters, the Japanese agency found “the minerals in sea mud extracted from depths of 3,500 to 6,000 meters (11,500-20,000 ft) below the ocean surface at 78 locations.” “One-third of the sites yielded rich contents of rare earths and the metal yttrium.” The deposits, in international waters in an area stretching east and west of Hawaii, as well as east of Tahiti in French Polynesia, are estimated to contain 80- to 100 billion tons of rare earth elements which could be extracted by simple acid leaching.
A letter in the British journal Nature Geoscience gives a little more detail:
World demand for rare-earth elements and the metal yttrium—which are crucial for novel electronic equipment and green-energy technologies—is increasing rapidly. Several types of seafloor sediment harbor high concentrations of these elements. However, seafloor sediments have not been regarded as a rare-earth element and yttrium resource, because data on the spatial distribution of these deposits are insufficient. Here, we report measurements of the elemental composition of over 2,000 seafloor sediments, sampled at depth intervals of around one meter, at 78 sites that cover a large part of the Pacific Ocean. We show that deep-sea mud contains high concentrations of rare-earth elements and yttrium at numerous sites throughout the eastern South and central North Pacific. We estimate that an area of just one square kilometer, surrounding one of the sampling sites, could provide one-fifth of the current annual world consumption of these elements. Uptake of rare-earth elements and yttrium by mineral phases such as hydrothermal iron-oxyhydroxides and phillipsite seems to be responsible for their high concentration. We show that rare-earth elements and yttrium are readily recovered from the mud by simple acid leaching, and suggest that deep-sea mud constitutes a highly promising huge resource for these elements.
It remains to be seen if these very deep resources can actually be economically recovered.