Abstract:
Despite the fact that previous studies have been conducted in great detail on oceanic ferromanganese nodules, research on the ferromanganese nodules located on marginal sea slope seamounts remains relatively insufficient. In this study, the ferromanganese nodule collected from Lichun Seamount on the northern slope of the South China Sea was selected as the research subject. By comprehensively employing analytical techniques such as XRD mineralogy, LA-ICPMS in-situ major and trace element geochemistry, and layered isotope geochemistry, the origin and material source of the ferromanganese nodule in Lichun Seamount, northern South China Sea, were investigated.The results reveal that the ferromanganese nodule in Lichun Seamount exhibits four distinct layers (layer 1, layer 2, layer 3, and layer 4), and the mineral composition of each unit layer varies, implying that it has experienced different hydrodynamic conditions and terrigenous input rates during its formation. This nodule is mainly composed of vernadite, quartz, and plagioclase. However, in addition to vernadite, the manganese-phase minerals in layer 3 and layer 4 also contain birnessite and todorokite, suggesting a diagenetic origin. The results of principal component analysis indicate that the ferromanganese nodules in Lichun Seamount are characterized by multi-stage and multi-source mineralization, with the main mineralization features being the formation of iron-phase minerals and the growth of manganese-phase minerals. The Mn/Fe ratio was less than 2.5 at most of the points in each layer, while at a few points in layer 3 and layer 4, the Mn/Fe ratio was greater than 2.5 or even exceeded 5. The REY partition pattern of the detection points within the nodule displayed a strong positive Ce anomaly, and most of them were mirror-symmetric with the South China Sea seawater. The REY partition pattern of a few detection points in layers 3 and 4 was similar to that of the sediment pore water. The Sr-Nd isotope is located between and close to the South China Sea seawater and sediment, and the Pb isotope exhibits the provenance characteristics of Taiwan Island. Therefore, the ferromanganese nodule in Lichun Seamount is mainly of hydrogenetic origin, with a small amount of diagenetic components incorporated during the later growth stage. The materials mainly originate from the surrounding seawater and are also influenced by the input of terrigenous materials from Taiwan Island.