Occurrence of REY-rich mud in the Pigafetta and East Mariana basins, western Pacific

Abstract

There is a growing interest in pelagic sediments enriched in rare earth elements and yttrium (REY) as one of the new mineral resources in the deep-sea. The Pacific Ocean, where much of the seafloor lies below the calcium compensation depth, has preferable conditions for the REY-rich mud to accumulate. The western Pacific was initially estimated to have a lower potential for REY than other parts of the ocean with stronger hydrothermal influence, but reports of extremely high levels of REY in sediments around Minamitori Island (Japanese EEZ) indicate that a reevaluation is needed. We analyzed the piston cores from the abyssal plains of the Pigafetta and East Mariana basins, western Pacific. The dominant lithology was brown pelagic clay, consisting of varying amounts of Fe-Mn (oxyhydr)oxides, zeolite (phillipsite), and biogenic calcium phosphate in addition to clay-sized particles. Bulk chemical analysis confirmed the presence of REY-rich mud (∑REY > 400 ppm) in the studied cores. While surface sediments contained respectable amounts of REY, the maximum concentrations were reached at certain depths. The covariation of total REY and P contents along the depth profile, together with the REY patterns characterized by the negative Ce anomaly and the HREE enrichment, supports that bioapatite is the major host of REY. Our results are generally consistent with the previous results from the Japanese EEZ in the north of the stu