Geochemical characteristics and genesis of the ferromanganese nodules in the middle western margin of the Parece Vela Basin

Deep-sea ferromanganese nodules have been widely recognized as important records of the geological events and the climatic and environmental changes of deep oceans. They are also commonly regarded as potential resources in near future for their richness in a variety of valuable metals. In this paper, 12 stations of ferromanganese nodule are newly discovered from the middle of western margin of the Parece Vela Basin and samples collected and analyzed for their geochemical characteristics. These ferromanganese nodules are low in Mn, Ni, Cu and Mo (8.20%～25.24%, 0.11%～0.54%, 0.08%～0.31% and 0.01%～0.03%, respectively), high in Ti, REY (0.45%～1.88% and 0.04%～0.19%, respectively)and moderate in Co (0.06%～0.27%) when compared to the high potential areas of the global oceans such as CCZ, CIOB, PB and CI. The Ni, Cu and Mo are strongly enriched in manganese oxides, but the Ti and REY are mainly absorbed from ocean water by the iron oxyhydroxides, and the REY³⁺ with a monovalent element of similar size are easily replaced through coupled substitution by Ca²⁺ from the Ca phosphates in the iron oxyhydroxides. The Ce and Y show pronounced positive and negative anomalies in the REY_SN patterns, respectively. The Ce³⁺ oxidation and Ce⁴⁺ fixation occur easily on the surface of the ferromanganese nodules. Once the Ce³⁺ in the ferromanganese nodules is oxidized to Ce⁴⁺, it is usually less mobile and will participate less in exchange reactions with the surrounding seawater. With time, this oxidative scavenging of Ce results in the preferential accumulation of redox-sensitive Ce relative to the non-redox-sensitive REY, but part of the Y is desorbed easily from the ferromanganese nodule surface, which produces positive Ce anomalies and negative Y anomalies. The research area is relatively young, and the growth of the ferromanganese nodules is not sufficient. Moreover, the surrounding terrain of the Parece Vela Basin is relatively high and there are less gateways connecting with the outside, which prevents the large-scale entry of the cold, dense and dissolved oxygen-rich bottom water such as Antarctic bottom water. The ferromanganese nodules of the region is dominated by hydrogenetic precipitation. However, the supply of the diagenetic precipitation components is too low, which will reduce the contents of valuable metals in the research aera. Therefore, it is low in resource potential.