Geochemical characteristics and resource significance of polymetallic nodules and cobalt-rich crusts in the southern Kyushu-Palau ridge

Deep-sea polymetallic nodules and cobalt-rich crusts are abundant in a variety of valuable metals with great resource potential. In this paper, 6 polymetallic nodules and 2 cobalt-rich crusts were collected from the southern section of the Kyushu-Palau ridge at a depth of about 3 000 m and their geochemical characteristics were analyzed and revealed. Results show that the Mn/Fe ratios of the samples range from 0.88 to 1.07, and the contents of Co and rare earth elements are high, which is similar to the polymetallic nodules in Cook Islands, showing typical hydrodiagenetic nodules and crusts. Compared to other high potential areas of the global ocean, our samples have higher Ca content, which might be related to the shallow water depth (above the carbonate compensation depth). Negative Y anomaly and high Nd content show characteristics of hydrogenic origin, but the weak positive Ce anomaly makes it different from other hydrogenic nodules/crusts, showing strong negative Ce anomaly, indicating that the samples grew in a weak oxidation environment. Therefore, distribution above CCD, growth in weak oxidation environment, and unique elements characteristics manifested that the nodule in the study area is a new type of polymetallic nodules, and the study of its elements source and mineralization mechanisms will provide a new insight to understand the formation and distribution of polymetallic nodules. In addition, with high Co and rare earth elements content, and shallow distribution, nodules and crusts in this area are easy to exploit with promising resource potential.