For cobalt-rich crusts in a contract area, the regular-shaped cells for relinquishment are obviously different from the natural ore distribution, and this brings challenges in evaluating the resources within them. Based on survey data in the China Ocean Mineral Resources Research and Development Association (COMRA) contract area, this study analyzed factors that could influence the relinquishment of cobalt-rich crusts. According to the guidelines of the International Seabed Authority, each original block of the COMRA contract area was subdivided into 16 cells. The contract areas were then divided into orebodies, unclear areas, and non-resource areas based on the distribution of the orebodies. Then, these attributions were assigned to the cells and the resources inside each cell were evaluated and identified, according to resource quantity, as resource cells, unclear cells, and non-resource cells. Finally, relinquishment was assessed by a step-by-step method in the following priority order: non-resource cells, unclear cells, and resource cells. This method was applied to the Caiqi Guyot (a guyot in the COMRA contract area) as a case study. The results show that the proposed method is suitable for the relinquishment of cobalt-rich crusts in the COMRA contract area and can also be applied to other contract areas worldwide.

The Clarion–Clipperton Fracture Zone of the east Pacific contains numerous shallow buried nodules that are in direct contact with pore water in sediment, providing a direct reflection of the interaction between nodules and sediment. However, research on the geochemical behavior of these shallow-buried nodules is limited. This study used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) to compare mineral and element distribution in shallow buried nodules with surface nodules. The shallow buried nodules are products of nodules entering the burial stage. In comparison to surface nodules, shallowly buried nodules develop a fourth oxidized-suboxic diagenetic growth layer after entering the burial stage, in addition to the three main growth inner layers (L1, L2, L3). We suggest that L4 is not influenced by the bottom water source and that the presence of todorokite and the high flux of Mn²⁺ in the sediment pore water compete with other metal elements to enter the lattice of manganate, resulting in significantly higher Mn, W, and Li contents in L4 compared to L2. However, the content of Ni, Mg, and other hydrogenetic elements is much lower in L4 compared to L2. We suggest that the instantaneous change in surface primary productivity results in a sudden shift in the redox environment of the upper sediment layer. This reaction leads to the reduction of solid-phase Mn, providing growth opportunities for the buried nodules. Simultaneously, this may also be the reason why the growth layer of the nodules is jointly controlled by the sedimentary processes of hydrogenetic, oxic diagenetic, and suboxic diagenetic processes.