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<p>Oceanic phosphatization events episodically precipitate carbonate fluorapatite (CFA), inducing phosphatization of ferromanganese crusts and significantly influencing rare earth elements plus yttrium (REY) and associated metal concentrations. Western Pacific ferromanganese crusts archive multiple phosphatization events, yet the absence of accurate chronological constraints hindered detailed investigations into the mechanisms of REY redistribution during distinct phosphatization episodes. Building upon previously established phosphatization events through CFA U-Pb geochronology, this study investigates three ferromanganese crusts from different water depths on Ita Mai Tai Guyot (Western Pacific) to evaluate the impacts of phosphatization on REY enrichment. Results show that all three hydrogenetic crusts experienced phosphatization, with phosphatized layers exhibiting higher average REY concentrations (2090, 1885, and 1854 ppm) than non-phosphatized layers (1413, 1174, and 1519 ppm), indicating that phosphatization enhances REY enrichment. However, when the crusts are precisely divided based on phosphatization episodes, one phosphatized layer (1293 ppm) exhibits lower REY concentrations than the unphosphatized layer (1413 ppm). This is attributed to a dilution effect from the precipitation of REY-poor authigenic CFA; the apatite within this specific layer contains only 602 ppm REY, a value lower than that of the unphosphatized crust. Concurrently, “REY-rich” vein-like CFA (2703 ppm) is associated with slow depositional processes, indicating its potential to increase the REY content of crusts. Therefore, this study reveals the dual role of phosphatization on REY enrichment. It can either promote enrichment by enhancing REY adsorption onto iron-manganese oxides and by forming REY-rich CFA, or cause dilution through the precipitation of REY-poor CFA. The net effect is ultimately controlled by a combination of environmental factors, including sedimentation rate and water depth, revealing the complex mechanisms of REY in phosphatized ferromanganese crusts.</p>

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Dual effects of phosphatization events on the enrichment of rare earth elements in Western Pacific ferromanganese crusts

  • 期刊论文

  • 发表日期：

    2025年10月17日

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  • Jinzhou Peng,
  • Dengfeng Li,
  • Xiaoming Sun

摘要

Oceanic phosphatization events episodically precipitate carbonate fluorapatite (CFA), inducing phosphatization of ferromanganese crusts and significantly influencing rare earth elements plus yttrium (REY) and associated metal concentrations. Western Pacific ferromanganese crusts archive multiple phosphatization events, yet the absence of accurate chronological constraints hindered detailed investigations into the mechanisms of REY redistribution during distinct phosphatization episodes. Building upon previously established phosphatization events through CFA U-Pb geochronology, this study investigates three ferromanganese crusts from different water depths on Ita Mai Tai Guyot (Western Pacific) to evaluate the impacts of phosphatization on REY enrichment. Results show that all three hydrogenetic crusts experienced phosphatization, with phosphatized layers exhibiting higher average REY concentrations (2090, 1885, and 1854 ppm) than non-phosphatized layers (1413, 1174, and 1519 ppm), indicating that phosphatization enhances REY enrichment. However, when the crusts are precisely divided based on phosphatization episodes, one phosphatized layer (1293 ppm) exhibits lower REY concentrations than the unphosphatized layer (1413 ppm). This is attributed to a dilution effect from the precipitation of REY-poor authigenic CFA; the apatite within this specific layer contains only 602 ppm REY, a value lower than that of the unphosphatized crust. Concurrently, “REY-rich” vein-like CFA (2703 ppm) is associated with slow depositional processes, indicating its potential to increase the REY content of crusts. Therefore, this study reveals the dual role of phosphatization on REY enrichment. It can either promote enrichment by enhancing REY adsorption onto iron-manganese oxides and by forming REY-rich CFA, or cause dilution through the precipitation of REY-poor CFA. The net effect is ultimately controlled by a combination of environmental factors, including sedimentation rate and water depth, revealing the complex mechanisms of REY in phosphatized ferromanganese crusts.