Geological and geochemical characteristics of shallow-buried ferromanganese crusts from Weijia Guyot and their resource potential

Numerous buried ferromanganese (Fe-Mn) crusts covered by surface sediments, such as foraminifera ooze, were found on the platforms of certain guyots in the Western Pacific Ocean. To examine the origin of these shallow-buried (<100 cm below the seafloor) Fe-Mn crusts and evaluate their resource potential, we conducted mineralogical and geochemical studies on seven drill cores from the Weijia Guyot(Ita Mai Tai Guyot), which is in the Co-rich Fe-Mn crust contract area of the China Ocean Mineral Resources Research and Development Association (COMRA).The buried Fe-Mn crusts exhibit multilayer structures and are composed of disordered vernadite, similar to the exposed Fe-Mn crusts. Moreover, they show comparable contents of major metallogenic elements (e.g., Mn, Cu, Co, and Ni) and platinum group elements when compared to exposed Fe-Mn crusts. However, they have much higher contents of rare earth elements (REEs) than those of exposed Fe-Mn crusts, indicating a comparable resource potential. The high P contents and collophanite observed in the petrographic microscope indicate that an evident phosphatization event occurred. Based on the tectonic evolution and sedimentation rate, we infer that the phosphatization event mainly took place before the crusts were buried. The phosphatization of shallow-buried Fe-Mn crusts results in an enrichment of REEs and their fractions. This process can also modify the sedimentary environment for Ce precipitation, which may, in turn, alter the diagenetic microenvironment of the shallow-buried Fe-Mn crusts. The mineralogical and geochemical results reveal that burial doesn't cause a significant difference between shallow-buried and exposed Fe-Mn crusts from Weijia Guyot, and they are still of hydrogenetic origin. The findings and research on shallow-buried Fe-Mn crusts indicate that they have comparable resource potentials with exposed Fe-Mn crusts. These results will influence future decisions related to the exploration, exploitation, and utilization of Co-rich Fe-Mn crusts in the contract area of COMRA. Furthermore, it could provide valuable insights for other contractors investigating the platform.