Mechanism and Influencing Factors of REY Enrichment in Deep-Sea Sediments

Abstract

Deep-sea sediments with high contents of rare-earth elements and yttrium (REY) are expected to serve as a potential resource for REY, which have recently been proved to be mainly contributed by phosphate component. Studies have shown that the carriers of REY in deep-sea sediments include aluminosilicate, Fe-Mn oxyhydroxides, and phosphate components. The ∑REY of the phosphate component is 1–2 orders of magnitude higher than those of the other two carriers, expressed as ∑REY = 0.001 × [Al2O3] − 0.002 × [MnO] + 0.056 × [P2O5] − 32. The sediment P2O5 content of 1.5% explains 89.1% of the total variance of the sediment ∑REY content. According to global data, P has a stronger positive correlation with ∑REY compared with Mn, Fe, Al, etc.; 45.5% of samples have a P2O5 content of less than 0.25%, and ∑REY of not higher than 400 ppm. The ∑REY of the phosphate component reaches n × 104 ppm, much higher than that of marine phosphorites and lower than that of REY-phosphate minerals, which are called REY-rich phosphates in this study. The results of microscopic observation and separation by grain size indicate that the REY-rich phosphate component is mainly composed of bioapatite. When ∑REY > 2000 ppm, the average CaO/P2O5 ratio of the samples is 1.55, indicating that the phosphate composition is between carbonate fluoroapatite and hydroxyfluorapatite. According to a knowledge map of sediment elements, the phosphate component is mainly composed of P, Ca, Sr, REY, Sc, U, and Th, and its chemical composition is relatively stable. The phosphate component has a negative Ce anomaly and positive Y anomaly, and a REY pattern similar to that of marine phosphorites and seawater. After the early diagenesis process (biogeochemistry, adsorption, desorption, transformation, and migration), the REY enrichment in the phosphate component is completed near the seawater/sediment interface. In the process of REY enrichment, the precipitation and enrichment of P is critical. According to current research progress, the REY enrichment is the result of comprehensive factors, including low sedimentation rate, high ∑REY of the bottom seawater, a non-carbonate depositional environment, oxidation conditions, and certain bottom current conditions.

REE distribution in sequential leached phases from deep-sea polymetallic nodules and sediments

“…The carriers of REE in deep-sea nodules and sediments include Fe-Mn oxyhydroxides, phosphate components and clay minerals (Dubinin, 2004;Abbott et al, 2019;Hein et al, 2020). The content of REE in the phosphate component is 1-2 orders of magnitude higher than those of the other two carriers (Ren et al, 2021). Our results show that the main important carrier is the phosphate component but the other two carriers cannot be excluded.…”

REY in pore waters of sediments hosting Fe-Mn nodules of the Interoceanmetal exploration area in the Clarion-Clipperton Fracture Zone, NE Pacific

“…The same station shows the highest REY contents of both sediments and pore waters that suggest some input from the neighboring volcanoes (Hikov et al, 2022). Elevated phosphorous content may also play an important role for the REE accumulation (Ren et al, 2021) for this station.…”

A Global Marine Sediment Compilation and a Cerium Anomaly Perspective on Metasomatized Mantle Sources for REE‐Mineralized Carbonatites

“…We obtained a compilation containing ∼6,000 REE analyses of modern marine sediments (Ren et al, 2021). The compilation includes data from the Atlantic, Pacific, and Indian oceans, and typically includes the top few of meters to tens of meters below the sea floor (Y.…”

“…There was no attempt to separate REE contributions from specific sediment fractions, such as clay, carbonate, phosphate, or nodules. REE patterns from the previously compiled marine sediment data (Ren et al, 2021) and the newly acquired Mianning-Dechang rock samples were analyzed using the lambda method via the online BLambdaR application (Anenburg & Williams, 2022). This method allows deconvolution of various curvature components of patterns into independent coefficients (Anenburg & Williams, 2022;O'Neill, 2016).…”