Perspectives of Mining in Pacific Ocean

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PUBLISHED ONLINE: 3 JULY 2011 | DOI: 10.1038/NGEO1185

Deep-sea mud in the Pacific Ocean as a potential resource for rare-earth elements Yasuhiro Kato1 *, Koichiro Fujinaga1 , Kentaro Nakamura2 , Yutaro Takaya1 , Kenichi Kitamura1 , Junichiro Ohta1 , Ryuichi Toda1 , Takuya Nakashima1 and Hikaru Iwamori3 World demand for rare-earth elements and the metal yttrium—which are crucial for novel electronic equipment and green-energy technologies—is increasing rapidly1–3 . Several types of seafloor sediment harbour high concentrations of these elements4–7 . 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 metre, 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 kilometre, 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. At present, 97% of the world’s production of rare-earth elements and yttrium (REY) is accounted for by China, although China has only one-third of global reserves and the Commonwealth of Independent States, the United States, and Australia together have another one-third of reserves1 . China’s dominance pertains to heavy rare-earth elements (HREE; conventionally Gd to Lu, but Eu is included here), which are especially important materials for high-technology products including electric automobiles and flatscreen televisions8 . HREE reserves are almost all in ion-absorptiontype ore deposits in southern China, whereas light REE (LREE) can be obtained from carbonatite/alkaline igneous complexes in other countries1–3 . We report here the great potential of deep-sea REY-rich mud in the Pacific Ocean as a new mineral resource for REY, especially HREE, because the mud commonly has a higher HREE/LREE ratio than the southern China ion-absorption-type deposits, as described below. We studied drill core samples from 51 sites obtained by the Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) and piston core samples from 27 sites obtained by the Ocean Research Institute, the University of Tokyo (Supplementary Table S1), which cover a major portion of the Pacific Ocean (Fig. 1). Many of the DSDP/ODP holes penetrated a depth greater than 50 m below seafloor (mbsf), whereas most of the University of Tokyo piston

cores are ∼10 m long and some are less than 3 m long (Fig. 2 and Supplementary Fig. S1). We measured chemical compositions of 2,037 bulk-sediment samples to evaluate the potential of seafloor sediment as a REY resource (Supplementary Data S1 and also see Methods). REY-rich mud (generally metalliferous sediment, zeolitic clay, and pelagic red clay in lithology) is mainly distributed in two regions: the eastern South Pacific and central North Pacific (Fig. 1). In the eastern South Pacific (5◦ –20◦ S, 90◦ –150◦ W), the REY-rich mud has high REY contents, 1,000–2,230 ppm total REY ( REY) and 200–430 ppm total HREE ( HREE). REY contents of the mud are comparable to or greater than those of the southern China ion-absorption-type deposits ( REY = 500–2,000 ppm; HREE = 50–200 ppm; refs 9,10); notably, the HREE are nearly twice as abundant as in the Chinese deposits. The core profiles reveal that the REY-rich mud has...
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