Early diagenetic control on the enrichment and mobilization of rare earth elements and transition metals in buried ferromanganese crust

Ferromanganese crusts on seamounts represent a major reservoir of various critical metal elements (e.g., rare earth elements and transition metals) and hold substantial economic value. However, current research primarily focuses on crusts that are exposed to seawater, and little is known about the resource potential of buried crusts in sediments and the impact of early diagenesis on buried crusts. Here, we present in-situ high-resolution major and trace element analyses of a buried crust from the western Pacific Ocean to unravel how rare earth elements and transition metals are enriched and mobilized as burial. The elemental profiles of the buried crust indicate that as the crust is buried, dissolved nickel (Ni) and copper (Cu) are gradually released from it into the porewater. Manganese and cobalt (Co) contents of the buried crust remain relatively constant, while rare earth elements are incorporated into the buried crust. Collectively, the early diagenesis leads to the release of Ni and Cu into the porewater, whereas it facilitates the fixation of rare earth elements within the buried crust. Given the widespread distribution of buried crusts in modern oceans, they represent a potential resource for future economic extraction of critical metals, particularly rare earth elements and Co.