Elucidation of the REY-enrichment mechanism on deep sea floor based on high-dimensional statistical techniques and multi-isotope analyses

2019 Fiscal Year Final Research Report

• Project/Area Number: 18K14168
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 31020:Earth resource engineering, Energy sciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: Yasukawa Kazutaka 東京大学, 大学院工学系研究科(工学部), 講師 (00757742)
• Project Period (FY): 2018-04-01 – 2020-03-31
• Keywords: レアアース泥 / 海底鉱物資源 / 多変量解析 / 独立成分分析 / クラスター分析 / 同位体分析 / 深海堆積物 / 地球化学

Outline of Final Research Achievements

The purpose of this study was to clarify the genesis of “extremely REY-rich mud” around Minamitorishima Island, in the western North Pacific Ocean. In this study, I statistically analyzed a huge geochemical dataset composed of 1646 samples x 41 elemental contents by using independent component analysis and k-means cluster analysis. Then, five independent components and ten clusters were extracted. The spatial distribution of the geochemical clusters in the real space demonstrated that the extremely REY-rich mud is accompanied by sedimentary erosion, suggesting that an enhanced bottom current could have physically accumulated REY-hosting minerals in the sediment. In addition, Sr-Nd-Pb isotopic analyses were performed on the samples representing these 10 clusters. The results indicated that the detrital components of the REY-rich mud could have originated from the Taklimakan Desert and Izu-Bonin volcanos.

Free Research Field

資源工学，地球化学

Academic Significance and Societal Importance of the Research Achievements

本研究の学術的意義は，近年発展が目覚ましいデータ科学的アプローチを資源工学・資源地質学分野に応用することで，一見均質な深海粘土が化学組成の統計的な特徴により明瞭に区別できることを示し，海洋底層流の強化によるレアアース濃集鉱物の物理的選別作用が有望なレアアース資源の形成に寄与したことを明らかにした点にある．本研究により，現在および過去の海洋底層流の強弱や流路といった物理的因子が，有望なレアアース泥の分布を推定する上で考慮すべき重要事項となった．現代社会の様々なハイテク機器に欠かせないレアアースの新規資源探査における新たな指針を提示したという点で，本研究の社会的意義は非常に大きい．