Preliminary Economic Feasibility Study of Ferromanganese Nodule Mining by Mechanical Lifting and Small-Scale Collectors

Ferromanganese nodules have been recognized as a potential future metal source for over 50 years. Many research and development efforts have been conducted by many organizations. Most of the efforts have been concentrated into the mining technologies especially for hydraulic lifting through riser pipes with bulk-scale nodule collector. However, no commercial mining venture exists. Uncertainty in the economy of nodule mining is considered to be the reason for this. In order to improve the economy, a mining subsystem based on mechanical lifting and small-scale collectors is proposed and the preliminary economic feasibility is examined in this study. The benefit was at a favorable level compared with that using hydraulic lifting with bulk-scale collector. From the viewpoint of environmental impact assessment, environmental considerations of deep-sea sediment plume are explained.

Intermittent Beginning to the Formation of Hydrogenous Ferromanganese Nodules in the Vast Field: Insights from Multi-Element Chemostratigraphy Using Microfocus X-ray Fluorescence

Vast ferromanganese nodule fields have been found on the deep-sea floor of all oceans worldwide. They have received attention because they potentially provide high-grade metal resources to develop future high- and green-technology. However, how these vast nodule fields were formed and developed owing to their widespread nature or tendency to be denser with an increasing number of nodules has not yet been established. In this study, the fine-scale inner structure of nodules of various sizes was analyzed on the basis of chemical mapping using microfocus X-ray fluorescence. We found that nodules distributed in the vast field around Minamitorishima (Marcus) Island have several types of innermost layers, which correspond to different chemostratigraphic layers of nodules that have been previously reported by us in this region. As nodules grow in order from the center to the outside, the different types in the innermost layer indicate a difference in the timing of the beginning of their growth. Moreover, because the differences in the chemical features of each layer reflect differences in the composition of the original deep-sea water, our results imply that the beginning of nodule formation occurred intermittently at each time of a water mass replacement due to new deep-sea currents flowing into this region. We recognized that the northern part of the study area was dominated by large nodules that started to grow in relatively earlier times, while the southern part tended to have many nodules that grew in relatively later times. Based on these observations, we hypothesize that the intermittent beginning of nodule formation is governed by the northward inflow of the deep-sea current that originated from the Lower Circumpolar Deep Water for an extended time to form the vast nodule field. Because patterns in the timing of nodule formation were different in the eastern and western regions, we thus further propose that the topographic framework, i.e., the arrangement of individual large seamounts and the cluster of small knolls and petit-spot volcanoes, strongly regulates the flow path of the deep-sea current, even if the position of the entire seamount changes owing to plate motion. The deep-sea current might supply some materials to be nuclei, resulting in the nodule formation at the beginning of the process.

Three-Dimensional Structural Analysis of Ferromanganese Nodules from the Western North Pacific Ocean Using X-ray Computed Tomography

The three-dimensional layered growth structure of 934 ferromanganese nodule samples collected from dives in the Pacific Ocean around Minamitorishima Island was assessed using X-ray computed tomography (X-ray CT) to elucidate their growth history. The thickness of the layered structure measured in three orthogonal directions showed that the ferromanganese nodules grew equally in all directions regardless of shape and size. Based on differences in CT numbers, a layered structure was subdivided into sublayers I, II, III, and IV, which corresponded to petrological features. The nodules were then classified as Types I, II, III, and IV according to whether they had sublayers I, I and II, I–III, or I–IV, respectively. Correlations between the total thickness of the layers and the number of sublayers indicated that both represented the relative age of the nodules. Nodules with all these types were recovered from most of the sampling sites, and histograms of the total layer thickness at each dive site showed several peaks. These findings indicated that the initiation of nodule growth was intermittent, rather than simultaneous. Three distinct thickness peaks were found at many sites throughout the study area, suggesting that at least three nodule initiation events covering hundreds of kilometers initiated the growth of ferromanganese nodules.

The Mechanism of Microbial-Ferromanganese Nodule Interaction and the Contribution of Biomineralization to the Formation of Oceanic Ferromanganese Nodules

Ferromanganese nodules are an important mineral resource in the seafloor; however, the genetic mechanism is still unknown. The biomineralization of microorganisms appears to promote ferromanganese nodule formation. To investigate the possible mechanism of microbial–ferromanganese nodule interaction, to test the possibility of marine microorganisms as deposition template for ferromanganese nodules minerals, the interactions between Jeotgalibacillus campisalis strain CW126-A03 and ferromanganese nodules were studied. The results showed that strain CW126-A03 increased ion concentrations of Fe, Mn, and other metal elements in solutions at first. Then, metal ions were accumulated on the cells’ surface and formed ultra-micro sized mineral particles, even crystalline minerals. Strain CW126-A03 appeared to release major elements in ferromanganese nodules, and the cell surface may be a nucleation site for mineral precipitation. This finding highlights the potentially important role of biologically induced mineralization (BIM) in ferromanganese nodule formation. This BIM hypothesis provides another perspective for understanding ferromanganese nodules’ genetic mechanism, indicating the potential of microorganisms in nodule formation.

Assessment of potential efficient development of the World ocean ferromanganese nodules in the context of global copper, nickel, cobalt and manganese market evolution

The paper analyzes implications of ferromanganese nodule mining and copper, nickel, cobalt and manganese production for their land-based producers. Potential scenarios are considered for consumption development, onshore production and long-term development of these metals’ mineral bases through 2035. It is shown that each metal market could be undersupplied over this period; this shortage can be offset by deepsea production. However, conditions and deficit emergence for various metals vary greatly. As a result, coincidence of nodule mining with the earliest deficit signs in the remaining markets will lead to oversupply, which will negatively affect onshore production, new mining and exploration projects; this will also reduce profitability of deepsea mining even making it uneconomic. It is not until 2030 that nodule mining involving copper, nickel, cobalt and manganese production can be implemented with no negative effects for market players.

Understanding Mn-nodule distribution and evaluation of related deep-sea mining impacts using AUV-based hydroacoustic and optical data

In this study, ship- and autonomous underwater vehicle (AUV)-based multibeam data from the German ferromanganese-nodule (Mn-nodule) license area in the Clarion–Clipperton Zone (CCZ; eastern Pacific) are linked to ground-truth data from optical imaging. Photographs obtained by an AUV enable semi-quantitative assessments of nodule coverage at a spatial resolution in the range of meters. Together with high-resolution AUV bathymetry, this revealed a correlation of small-scale terrain variations (< 5 m horizontally, < 1 m vertically) with nodule coverage. In the presented data set, increased nodule coverage could be correlated with slopes > 1.8∘ and concave terrain. On a more regional scale, factors such as the geological setting (existence of horst and graben structures, sediment thickness, outcropping basement) and influence of bottom currents seem to play an essential role for the spatial variation of nodule coverage and the related hard substrate habitat. AUV imagery was also successfully employed to map the distribution of resettled sediment following a disturbance and sediment cloud generation during a sampling deployment of an epibenthic sledge. Data from before and after the “disturbance” allow a direct assessment of the impact. Automated image processing analyzed the nodule coverage at the seafloor, revealing nodule blanketing by resettling of suspended sediment within 16 h after the disturbance. The visually detectable impact was spatially limited to a maximum of 100 m distance from the disturbance track, downstream of the bottom water current. A correlation with high-resolution AUV bathymetry reveals that the blanketing pattern varies in extent by tens of meters, strictly following the bathymetry, even in areas of only slightly undulating seafloor (<1 m vertical change). These results highlight the importance of detailed terrain knowledge when engaging in resource assessment studies for nodule abundance estimates and defining mineable areas. At the same time, it shows the importance of high-resolution mapping for detailed benthic habitat studies that show a heterogeneity at scales of 10 to 100 m. Terrain knowledge is also needed to determine the scale of the impact by seafloor sediment blanketing during mining operations.