[S-CG48] Ocean Floor Geoscience

[SCG48-P36] Geochemical characterization of pelagic clay in the North Atlantic Ocean and its potential as a resource for rare-earth elements

*Naoto Takada¹, Kazutaka Yasukawa¹, Daiki Terauchi¹, Mitsuki Ogasawara¹, Marshel Emmanuelle Tampah¹, Mori Shunsuke¹, Sho Yoshida¹, Moei Yano^2,1, Shiki Machida^2,1, Kana Ashida², Yusuke Kuwahara^1,2, Junichiro Ohta^1,2, Koichiro Fujinaga^2,1, Kentaro Nakamura^1,2, Kato Yasuhiro^1,2 (1.School of Engineering, The University of Tokyo, 2.Ocean Resources Research Center for Next Generation, Chiba Institute of Technology)

Keywords:North Atlantic Ocean, pelagic clay, REE-rich mud, bulk chemical composition, seafloor mineral resources

Deep-sea sediments enriched in rare-earth elements (termed as “REE-rich mud”) are widely distributed in the eastern South and central North Pacific Ocean [1]. They are attracting our attention as a new seafloor mineral resource because the rare-earth elements are essential for various high-tech industries [1]. Furthermore, REE-rich mud with the world's highest total REE concentration reaching 6,800 ppm was discovered in the Japanese Exclusive Economic Zone around Minamitorishima Island [2]. The presence of REE-rich mud was also confirmed in the central and eastern Indian Ocean [3,4]. Many studies on distributions and origins of REE-rich mud have been conducted in the Pacific and Indian Oceans [1–5]. In the Atlantic Ocean, however, the presence of REE-rich mud has only been reported in near-surface sediments at a few sites [6], and the distribution of REE at a deeper part of the sediment column remains uncertain.
In this study, we analyzed legacy core samples of deep-sea sediments collected by Deep Sea Drilling Project/Ocean Drilling Program in the North Atlantic Ocean. Bulk chemical compositions of major and trace elements were determined by XRF and ICP-MS, respectively. The highest REE concentration is 868 ppm around 330 m below the seafloor in the eastern North Atlantic Ocean. Elemental relationships in the North Atlantic sediments indicate that hydrogenous component, as well as biogenic calcium phosphate, strongly contributes to bulk chemical composition, including REE concentration, of the layers enriched in REE. A simple flux model of the REE sedimentation from seawater suggests that the sedimentation rates of bulk sediment required for the REE concentrations are consistent with the values described in or estimated from each cruise report. This indicates that the REE-enrichment in the North Atlantic Ocean is likely to be controlled by a sedimentation rate. Although further investigations of other areas are needed, the potential of the North Atlantic pelagic clays used in this study as a REE resource seems to be limited, comparing with that of the Pacific Ocean.

[1] Kato et al. (2011) Nature Geoscience, 4, 535–539. [2] Iijima et al. (2016) Geochemical Journal, 50, 557–573. [3] Yasukawa et al. (2014) Journal of Asian Earth Sciences, 93, 25–36. [4] Zhang et al. (2017) Journal of Rare Earths, 35, 1047–1058. [5] Liao et al. (2022) Chemical Geology, 595, 120792, [6] Menendez et al. (2017) Ore Geology Reviews, 87, 100–113.