Ferromanganese Nodules: Rare Earth Element Mineralization Potential and Their Role as a Quaternary Paleoenvironmental Record

Abstract

Ferromanganese nodules are characterized by their concentrically layered structure and slow growth rates on the scale of several mm/Ma. During their formation period, ferromanganese nodules incorporate trace elements, including rare earth elements, from their ambient seawater. The purpose of this study was to investigate the rare earth element mineralization potential of ferromanganese nodules in order to determine whether they are viable as resources for rare earth elements. Additionally, this study aimed to investigate the role of ferromanganese nodules as paleoenvironmental indicators by analyzing their trace element composition throughout the Quaternary period. The resultant data are used in conjunction with 10Be dating, and compared with known climatic events. Laser ablation inductively coupled plasma-mass spectrometry was used to investigate two hydrogenetic ferromanganese nodules sourced from the Campbell Nodule Field in the Bollons Seamount. The average REE data of both nodules are compared with those of the rare earth element deposits Steenkampskraal, Mountain Pass, Bayan Obo, Saint Honoré Complex, Strange Lake, and Thor Lake. The resultant ferromanganese nodule trace element data were also compared with the timings of the Mid-Pliocene Warming Period, the Mid-Pleistocene Transition, and the Marine Isotope Stage stratigraphic system, the latter of which corresponds closely with Milankovitch orbital forcing theory. It was found that the rare earth element concentrations of ferromanganese nodules 1365–B2 and 1365–BM were comparable with those of the heavy rare earth element deposits Strange Lake and Thor Lake, indicating that ferromanganese nodules have the potential to be heavy rare earth element resources. Additionally, it was found that nodules 1365–B2 and 1365–BM displayed discrepancies in their trace element distribution patterns, possibly as a result of Deep Western Boundary Current and Antarctic Circumpolar Current influences on their growth rates. However, the trace element distribution profiles of both nodules, particularly nodule 1365–BM, correlated with the timing of the known climate events. Ultimately, these findings suggest that there is potential for ferromanganese nodules to be used as both rare earth element resources and paleoenvironmental indicators, albeit with certain caveats. More research still needs to be carried out to determine the extent of their usefulness in these two roles.