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Geochemical Journal, Vol. 50 (No. 6), pp. 575-590, 2016
doi:10.2343/geochemj.2.0432

Geochemistry of REY-rich mud in the Japanese Exclusive Economic Zone around Minamitorishima Island

Koichiro Fujinaga,1,2 Kazutaka Yasukawa,3,1 Kentaro Nakamura,3 Shiki Machida,4 Yutaro Takaya,5,2,4 Junichiro Ohta,6 Shuhei Araki,3 Hanjie Liu,3 Ryo Usami,3 Ryota Maki,3 Satoru Haraguchi,6 Yoshiro Nishio,7 Yoichi Usui,4 Tatsuo Nozaki,4,8,2 Toshitsugu Yamazaki,9,10 Yuji Ichiyama,11 Akira Ijiri,12,4 Fumio Inagaki,12,4 Hideaki Machiyama,4 Koichi Iijima,4 Katsuhiko Suzuki,4 Yasuhiro Kato2,3,1,4* and KR13-02, MR13-E02 Leg 2 and KR14-02 Cruise Members

1Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
2Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
3Department of Systems Innovation, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
4Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan
5Department of Resources and Environmental Engineering, School of Creative Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjyuku-ku, Tokyo 169-8555, Japan
6Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan
7Department of Marine Resource Sciences, Faculty of Agriculture and Marine Science, Kochi University, 200 Monobe Otsu, Nankoku, Kochi 783-8502, Japan
8Department of Planetology, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan
9Department of Ocean Floor Geoscience, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan
10Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8561, Japan
11Department of Earth Sciences, Faculty of Science, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
12Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe Otsu, Nankoku, Kochi 783-8502, Japan

(Received March 8, 2015; Accepted June 25, 2016)

Abstract: We report detailed lithological and chemical characteristics of deep-sea sediments, including rare-earth elements and yttrium-rich mud (REY-rich mud), in the Japanese Exclusive Economic Zone (EEZ) around Minamitorishima Island. Three research cruises obtained fourteen sediment cores collected by piston coring. Based on the visual descriptions and geochemical analysis of the sediment cores, we confirm the presence of REY-rich mud containing more than 400 ppm total REY (ΣREY) in the southern and northwestern areas of the Minamitorishima EEZ. The REY-rich mud layers are characterized by abundant grains of phillipsite, biogenic calcium phosphate, and manganese oxides, and are widely distributed in relatively shallow depths beneath the seafloor. In contrast, relatively thick, non-REY-rich mud lies near the seafloor in the northern areas of the EEZ. In the three cores from the southern part of the EEZ, we also confirm the presence of highly/extremely REY-rich mud layers. Further accumulation of geochemical data from the sediments will be required to constrain the extent of the highly/extremely REY-rich mud layers.
Key words: REY-rich mud, rare-earth elements, geochemistry, deep-sea mineral resources, Minamitorishima Island


*Corresponding author E-mail: ykato@sys.t.u-tokyo.ac.jp


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