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Rough surface of the pellet and the particle size effect limit better application of pressed pellet sample preparation to wavelength dispersive X-ray fluorescence spectrometry (WDXRF) for determination of multi-element composition in cobalt-rich crust samples. This paper explored the technique for preparing ultrafine powder of cobalt-rich crust samples by wet grinding, and an ultrahigh-pressure system was used to prepare pellets for WDXRF. Ultrafine cobalt-rich crust samples having 99% of the particle size < 4 μm (D99 < 4 µm) with narrow size distribution were successfully prepared. The advantages of the new approach were investigated and the developed WDXRF method was validated. Results showed that the detection limit and precision of the proposed method for major components were improved. The detection limit of the method was within the interval from 7.0 to 1704 μg/g, and the results of precision test showed that the relative standard deviation of the measured values of components was improved to between 0.2% and 1.6%. The present method was applied to determine major, trace and rare earth components in cobalt-rich crust samples, a good agreement was achieved between the reference and measured values with relative percentage difference not more than 6.7%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Systematic and detailed in-situ geochemistry analyses are utilized for the Co-rich crust from the Magellan Seamounts in the Western Pacific. • The expansion of the oxygen-minimum zone over the seamount can promote the Co enrichment during the growth period. • The presence of abundant detrital minerals and clay minerals is not conducive to Co enrichment. • The phosphatization was firstly proved to be critical for the secondary Co enrichment in the Co-rich crust. Marine cobalt-rich (Co-rich) crusts are submarine critical metal resources with high economic value. In this study, detailed in-situ fine-scale morphological, mineralogical, and geochemical analyses were conducted on Co-rich crust from the Western Pacific. The Co-rich crust can be divided into three layers: (1) Layer 1 is the oldest anthracite layer and contacts with the substrate, showing a very dense laminated/columnar texture. Layer 1 can be further divided into two distinct sublayers: a lower black, massive, dense sublayer (Layer 1–1) and an upper black-to-brown sublayer (Layer 1–2). (2) Layer 2 is porous and locally vuggy, and its pore space is filled with a large amount of silicate detrital minerals and clay minerals. (3) Layer 3, on the top, is black and dense, with a dendritic, columnar/laminated texture. Co is very unevenly distributed throughout the whole crust, with three distinct Co-rich areas. Layer 3 is a typical hydrogenetic crust and has not undergone late alteration. The main processes for Co enrichment are specific adsorption-oxidation on Mn-oxides and the structural incorporation of Co3+ into Mn-oxide phases. The average Co content of the Layer 3 is much higher than that of the other two layers. The presence of abundant detrital and clay minerals, along with high levels of Al, Si, and Ti in Layer 2, indicates the incorporation of terrigenous material, resulting in a high average growth rate. However, these processes are not conducive to Co enrichment. In the phosphatized Layer 1, fluctuations in element content are significantly greater than in the upper, non-phosphatized layers. Phosphatization has resulted in the partial decomposition of the initial Co-rich micro-layers, which may have reactivated and migrated Co, contributing to secondary Co enrichment. [ABSTRACT FROM AUTHOR]

To mine the cobalt-rich crust deposits at the substrate of the slope of the seamount, the mining vehicle needs to walk on the slope and strip the cobalt-rich crust from the substrate. To achieve safety and control, the vehicle needs to stably walk on the slope. In this paper, we propose a modeling method for mining vehicle performance based on slope stability and antislip and antiskid conditions. The specific energy of three types of mining vehicles is compared based on dimensionless parameters. The dual-drum type is determined to be the best choice in terms of energy costs, followed by the down-milling type. The performance of the compact mining vehicle based on different slope angles and two sea trial results in the South China Sea indicate that the slope angle, substrate, and crust have significant effects on the stability. The modeling method proposed in this paper can help designers estimate the structure and power of mining vehicles based on mining stability. [ABSTRACT FROM AUTHOR]

Conical picks are the core component of deep-sea mining vehicle in cobalt-rich crust cutting, and its cutting modes directly affects the deep-sea mining vehicle performance. In order to study the cutting modes and the influence of cutting modes on their comprehensive properties, the cobalt-rich crust cutting model is established by discrete element method, and the cobalt-rich crust crack evolution process, cutting modes and the forming law of broken block are studied in deep-sea environment. On this basis, a comprehensive evaluation model for the cutting performance based on each performance index game is established, the mapping relationships between the number of cracks, the length of lateral cracks, the specific energy and the comprehensive performances are studied. The results show that the cutting mode and comprehensive performance are different among different cutting parameters. According to the crack propagation, the cutting modes can be divided into mode I, mode II and mode III. The comprehensive performance of mode III is the best, mode II is the second and mode I is relatively worst under the same working conditions. [ABSTRACT FROM AUTHOR]

Cobalt-rich crust is a seabed metal mineral resource that is different from oceanic polymetallic nodules. Based on the higher Co content than polymetallic nodules, the commercial value of cobalt-rich crust may be better than that of polymetallic nodules. Due to the special distribution of valuable metals, commercial implementation is always limited. Herein, a novel process is proposed to efficiently and, in an eco-friendly way, recycle valuable metals from cobalt-rich crust. The results indicate that carbon could promote the decomposition of manganite in the cobalt-rich crust during the acid baking process, and the leaching ratio of Mn could increase by 50% when carbon is added during acid baking. In addition, it can be found that the promotion of carbon for Co is stronger at low sulfuric acid consumption than that at high sulfuric acid consumption; however, there is no promotion of carbon for leaching Ni and Cu during the acid baking process. The leaching ratio of Ni, Co, Cu, Mn, and Fe reached 98.59%, 91.62%, 93.81%, 41.27%, and 26.94%, respectively, when the mass ratio of the sulfuric acid and cobalt-rich crust was 0.567, the mass ratio of the carbon and cobalt-rich crust was 0.1, the temperature was 200 °C and the time was 240 min. This research could provide an alternative economic process for recycling valuable metals from cobalt-rich crusts. [ABSTRACT FROM AUTHOR]

In order to study the cobalt-rich-crust cutting mechanism of conical picks under conditions of different types of joints, a simulation model of cobalt-rich-crust cutting is establish based on the discrete element method. The cutting pattern, cutting efficiency, crack growth ability, and size of broken cobalt-rich crust are analyzed and similar cutting experiments are conducted. The results thus obtained show that the cutting pattern is directly affected by the joint of the cobalt-rich crust and bedrock and the cutting space and load modes, and there are six basic cutting patterns under various working conditions. As the joint angle is increased, the cutting efficiency of the conical pick decreases gradually. The cutting efficiency of a simultaneous pattern is greater than that of a sequential pattern. When the cutting space is less than 35 mm, the size of the broken cobalt-rich crust produced using the simultaneous pattern is smaller than that produced using the sequential pattern. The cutting experiments verify the accuracy of the simulation. [ABSTRACT FROM AUTHOR]

Cobalt-rich crusted deposits are found all over the world’s oceans, and their distribution is closely related to the submarine topography. The determination of crusting area is the basic work for the exploration and mining of these deposits. Many factors affect the accumulation of crusts, and topography is a crucial factor. Mineralization forecast requires comprehensive consideration of geological background and experts’ views and opinions, the prior knowledge of prospectors is the biggest factor affecting the results. In the course of ocean research, especially with the rapid development of space information technology, a huge amount of ocean data that cover about 70% of the total surface area have been accumulated rapidly; how to extract valuable information from large, fast, complex, and multisource data has become a hot topic in current ocean research. Machine learning- and deep learning-related research methods can read feature signs from mineral data to obtain existing mineral knowledge to further serve mine prediction work. Based on the study of terrain features of cobalt-rich crust in high-producing areas, the numerical matrix of altitude of 1 km2 ocean surface was obtained, with the geographical coordinates of cobalt-rich crust sites as the center. Using the analysis method of convolutional neural network, the numerical matrix is trained to learn regional features such as slope and flatness and to distinguish the cobalt-rich crust–crust site topography from other submarine topography. According to the training model, the high-producing cobalt-rich crusting area was predicted and better forecasting value is obtained. Meanwhile, the accuracy of the selection of crusting target area was improved by combining the influence of other factors.

This paper proposed a compact design of the subsea cobalt-rich crust mining vehicle with a general purpose support vessel for subsea resource exploration, sample collection, and research. The necessary functions were considered in the concept design, including walk, crushing/mining, sample collection, cutter head adaptation, vehicle orientation, crust texture measurement, awareness, positioning, and navigation. The prototype was tested in both tank and subsea environment. The sea trials were carried out with the support of a general purpose support vessel. The track design worked well in both the tank and subsea environment and the mining vehicle walked smoothly in the sea trial. The crust was crushed to the size of 2 mm and 10 mm with different cutting parameters and successfully collected by the jet pump, 6 kg in total. The crust texture was measured by the onboard sonar successfully and can be used for cutting parameter selection. The cameras captured the images of the subsea environment, but the actions of crushing and sample collection produced plumes, which blocked the camera vision. In the situation, the front image sonar can be used to keep the vehicle away from big rocks. The mining vehicle is not limited to the mining and sampling of subsea cobalt-rich crust. Most of the subsea solid resources on the seabed can be considered to use the compact mining vehicle for sampling and related research. The only issues to be considered are the crushing ability and sample size required.

Keywords: Cobalt-rich crust; Compressive strength; Abrasivity; Friability; Cutting test EN Cobalt-rich crust Compressive strength Abrasivity Friability Cutting test 2929 2934 6 06/05/20 20200601 NES 200601 Introduction Hydrogenetic cobalt-rich ferromanganese crusts (cobalt-rich crusts, CRCs) are expected as potential mineral deposits for rare earth elements and platinum group elements as well as cobalt, nickel, and manganese (Manheim [8]; Rona [13]). Thereafter, Yamazaki et al. ([17]) reported the compressive strength of CRCs and substrate rocks, and then Wu and Chen ([16]) reported the shear strength of CRCs. 1 Porosity, P-wave velocity, and uniaxial compressive strength of the cobalt-rich crusts (CRCs) and substrate rocks. a Relation between porosity and uniaxial compressive strength. The curves for the CRCs are located on the left side of those for the substrate rocks; that is, the debris of the CRCs is smaller than that of the substrate rocks after crushed. [Extracted from the article]

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The spatial distribution of cobalt-rich crust thicknesses on seamounts is partly controlled by water depth and slope gradients. Conventional distance–direction-based variogram have not effectively expressed the spatial self-correlation or anisotropy of the thicknesses of cobalt-rich crusts. To estimate resources in cobalt-rich crusts on seamounts using geostatistics, we constructed a new variogram model to adapt to the spatial distribution of the thicknesses of the cobalt-rich crusts. In this model, we defined the data related to cobalt-rich crusts on seamounts as three-dimensional surface random variables, presented an experimental variogram process based on the distance–gradient or distance–“relative water depth,” and provided a theoretical variogram model that follows this process. This method was demonstrated by the spatial estimation of the thicknesses of cobalt-rich crusts on a seamount, and the results indicated that the new variogram model reflects the spatial self-correlation of the thicknesses of cobalt-rich crusts well. Substituted into the Kriging equation, the new variogram model successfully estimated the spatial thickness distribution of these cobalt-rich crusts. [ABSTRACT FROM AUTHOR]

The uniaxial compressive breaking process of energy of deep-sea Cobalt-Rich Crust was selected as researching content, and the calculation of energy conversion of breaking Cobalt-Rich Crust under loading and unloading conditions was described in detail, and also the specimens of Cobalt-Rich Crust were tested in rock mechanical testing system under the specified stressing paths. From experimental data, the elastic energy, the dissipated energy and the total inputting energy of unloading points were analyzed systematically. The conclusions are as follows: (1) the specimens of Cobalt-Rich Crust are anisotropic rock, and different testing specimens need to load different axial forces to break, and the maximum of axial force is 8KN, and the minimum is 5KN; (2) when increasing the axial force, the elastic energy, the dissipated energy and the total inputting energy of the unloading points increased nonlienearly; (3) Cobalt-Rich Crust is not the same with other ordinary elastic rock, the elastic energy is lower than the corresponding dissipated energy, and with the increasing of the axial force, the difference between two values becomes more and more. [ABSTRACT FROM AUTHOR]

A method for determining levels of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) in marine geological samples using wavelength dispersive X-ray fluorescence is presented here. Samples are prepared as pressed powder pellets. The method makes full use of the advantages of the ability of the modern X-ray fluorescence spectrometer to detect ultra-light elements and high-powered X-rays. A series of calibration standards with an appropriate concentration range was developed using a standard addition method. Empirical coefficients were used to correct for matrix effects in the case of F and Cl, the rhodium Kα -Compton peak was used as internal standard for Br matrix corrections, and the rhodium Kb-Compton peak was used to correct for the matrix effect on I. For % concentration of the analyte, the precision (relative standard deviation) of the method was <5%. For concentrations <0.1%, the relative standard deviation depended heavily on the count rates (or concentration). The accuracy of the method was validated by comparison of the results to similar reference materials. The detection levels of this method (counting time100 s) were 100, 5, 0.5, and 10 µg g−1for F, Cl, Br, and I, respectively. The method was here used to determine the levels of halogens in samples of 19 marine sediments (China, Russia, Canada, American), 10 marine manganese nodules (China, Russia, American, Germany, India, Japan), 4 cobalt-rich crust reference materials (Russia, China), reference materials, and 3 phosphorites. [ABSTRACT FROM PUBLISHER]

Elemental geochemistry is an essential part of understanding mineralization mechanisms. In this paper, a data set of 544 cobalt crust samples from seamounts of the Western Pacific are used to study the enrichment characteristics of metal elements. REE normalization is utilized to reveal the origin of the crusts; effects of water depth on Co enrichment and impacts of phosphatization on mineral quality are discussed to obtain the evolution of these marine mineral deposits, which gives support to further resource assessment. Conclusions are reached as follows: 1) Elemental abundances, inter-element relationships, and shale-normalized REE patterns for phosphate-poor crusts from different locations reflect hydrogenetic origin of the crusts. EFs (enrichment coefficients) of REE exhibit exponential increase from surface sediments to phosphorite to polymetallic nodules to crusts, suggesting that the improved degree of hydrogeneous origin induces the enrichment of REE. 2) The crusts in the Western Pacific, formed through hotspot produced guyots trails, have relatively lower REE than those in the Mid-Pacific. The latter could be attributed to the peculiar submarine topography of seamounts formed by intraplate volcanism. 3) The non-phosphatized younger crust layers have 40% higher Co than the phosphatized older layers. This indicates the modification of the elemental composition in these crusts by phosphatization. A general depletion of hydroxide-dominated elements such as Co, Ni, and Mn and enrichment of P, Ca, Ba, and Sr is evident in phosphatized crusts, whereas non-phosphatized younger generation crusts are rich in terrigenous aluminosilicate detrital matter. 4) Co increases above the carbonate compensation depth (CCD) from less than 0.53% to over 0.65% in seamount regions with water depth of less than 2,500 m, suggesting the significance of the dissolution of carbonate in the sea water column to the growth and composition of crusts. [ABSTRACT FROM AUTHOR]

Confining pressure and cutting sequence of conical picks directly affect the ocean mining efficiency. The simulation model of cobalt-rich crust cutting with two-dimensional discrete element method is established to simulate the whole process of crack growth. According to the obtained crack growth patterns and the rules of fracture-block formation, four typical fracture modes are summarized, and the fracture mechanism is further studied from three aspects: the efficiency of cobalt-rich crust cutting, the ability of crack growth and the size of fracture-block. The results show that with the increase of confining pressure, the cutting efficiency and crack growth ability decrease, and the cutting efficiency of simultaneous loading is larger than that of the sequential loading, while the crack growth ability is just the opposite. In addition, the size of fracture-block is related to fracture modes. • At present, the research on fracture characteristics of cobalt-rich crust cutting in ocean environments are still in primary stage. • The four fracture modes of cobalt-rich crust cutting are first proposed creatively. • The optimal loading method under different confining conditions is determined. In this field, these studies are innovative. [ABSTRACT FROM AUTHOR]

Two records of the crust laminae from the Marcus-Wake Seamounts and the Magellan Seamount were biostratigraphically studied. Based on biological imprints of the calcareous nannofossils, the geological ages of the two records were determined, with CM1D03 from the Marcus-Wake Seamounts being of late Paleocene to Pleistocene and CM3D06 from the Magellan Seamount of Late Cretaceous (more than 70.0 Ma). There are the obvious temporal-spatial differences in the initial formation period and enrichment characteristics of the cobalt-rich crusts of the two seamount chains and differences in the combination and distribution of microfossils in the inner crust layers between the seamounts. These differences are due to the adaptabilities of oceanic species in different environments. Ecological research was carried out in terms of population size of the calcareous nannofossils preserved in the crustal layers to discern the relation of the geological events at the Eocene-Oligocene (E/O) transition. The results show the transitions and recombination of species in the biotic community during the E/O transition obviously corresponded to 25 mm depth in the CM1D03 crust and 58 mm depth in the CM3D06 crust. The changes in biological species and the formation of particular ecological structures indicate the adaptive response of the paleo-biological community in the western Pacific Ocean to the global cold-climate events and the close correlation between the formation of the crust and the global climate change. [ABSTRACT FROM AUTHOR]

Organic matter in cobalt-rich crust (CRC) from the Marcus-Wake Seamounts of the western Pacific Ocean, Sample CM1D03, has been analyzed to understand the source, geochemistry and mineralization of organic matter, and the mineralization environment. Biomarkers, including n-alkanes, isoprenoids, terpanes and sterols, have been detected in various layers of the CRC sample, using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The content of organic carbon (OC) and its stable isotope (δC), and the combined features of the biomarkers show that the mineralized organic matter in CM1D03 CRC was mainly derived from microorganisms and lower plankton (e.g., bacteria and algae, respectively) from marine surface water, with some terrestrial higher plant components. The ratio of chloroform bitumen 'A': OC was high in the CRC, between 10.51 and 20.66, showing significant migration characteristics of n-alkanes. Four mineralization categories of organic matter were recognized based on GC chromatograms of n-alkane molecules: (1) primitive type (bacteria and algae), which is characterized by moderately mature of n-alkanes preserving the original characteristics of the organic matter from microorganisms and lower plankton; (2) microbial degradation type, which is characterized by low contents of n-alkanes and rising baseline in the chromatogram, with the 'bulge' being the products of organic matter by biodegradation; (3) organic matter migration type, which is characterized by low carbon number of n-alkanes with nC as the main peak carbon, without odd even predominance, and low concentrations of isoprenoids and hydrocarbons with high carbon number; and (4) organic matter hydrothermal type, which is characterized by relatively low concentration of small molecular weight n-alkanes, pristane, and phytane, accompanied by higher concentration of n-alkanes with carbon number greater than nC. This study shows that biomarkers can record controlling factors of mineralization and their variation. [ABSTRACT FROM AUTHOR]

Aim The benthic fauna of seamounts typically includes organisms that are slow-growing, long-lived and sensitive to mechanical disturbance, making seamounts susceptible to anthropogenic impacts. Such impacts may arise from mining cobalt-rich crusts, envisaged for seamounts in the central North Pacific; this scenario requires that environmental guidelines for mining operations on seamounts be developed. Here, we provide the biological information essential for effective conservation planning of deep-sea features targeted for such mining. Location Central North Pacific, Hawaiian Seamount Chain. Methods Spatial analysis of seamount benthos using a large biological dataset (> 600 taxa) obtained from 144 submersible dives (depth range: 113-1985 m) on 27 seamounts covering a distance of over 2200 km of ocean. Results Benthic assemblages of invertebrates are structurally different between seamounts located inside and outside a region with cobalt-rich crusts. This spatial contrast results from variations in species composition and relative abundance of species, rather than differences in species richness, challenging historical notions of an impoverished cobalt-rich crust fauna in the region. Seamount assemblages also have high species turnover with depth and distance at the scale of individual seamounts, but geographic separation was a poor predictor of ecological separation for the region at large. Main conclusion Several implications for the design of spatial management and conservation tools with respect to mining emerge: (1) conservation of seamounts outside the cobalt-rich crust region is unlikely to capture the full range of ecological features found inside the region; (2) conservation areas need to encompass a broad bathymetric gradient; (3) ideally, mining blocks on individual seamounts should not exceed 2 km in length. Overall, the life history characteristics and morphological traits of the deep-water invertebrate fauna typical of seamounts in the region imply that any recovery from mechanical impacts is likely to be very slow. [ABSTRACT FROM AUTHOR]

A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age. The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous, late Paleocene, (early, middle, late) Eocene, middle Miocene, late Pliocene, and Pleistocene. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) were used to test the Co-rich crusts, and a variety of molecular fossils were detected, such as chloroform bituminous 'A', n-alkane, isoprenoid and sterol. Peak carbon and molecular indices (such as ΣC23−/ΣC24+, CPI, Pr/Ph, Pr/nC17, Ph/nC18 and δ13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter. Researches on calcareous nannofossils, molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene (P/E) global event is recorded in the cobalt-rich crusts from the northwestern Pacific Ocean. A succession of biomes can be observed near the 85 mm boundary (about 55 Ma), i.e., the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis, and Broisonia parka microbiotas above the P/E boundary, and the bloom of Coccolithus formosus, Discoaster multiradiatus, Discoaster mohleri and Discoaster sp. below the boundary. Typical parameters of molecular fossils, such as saturated hydrocarbon components and carbon-number maxima, Pr/Ph, Pr/C17, Ph/C18, distribution types of sterols, Ts/Tm ratios and bacterial hopane, also exhibit dramatic changes near the P/E boundary. These integrated results illustrate that the biome succession of calcareous nannofossils, relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event [ABSTRACT FROM AUTHOR]

This paper proposed a compact design of the subsea cobalt-rich crust mining vehicle with a general purpose support vessel for subsea resource exploration, sample collection, and research. The necessary functions were considered in the concept design, including walk, crushing/mining, sample collection, cutter head adaptation, vehicle orientation, crust texture measurement, awareness, positioning, and navigation. The prototype was tested in both tank and subsea environment. The sea trials were carried out with the support of a general purpose support vessel. The track design worked well in both the tank and subsea environment and the mining vehicle walked smoothly in the sea trial. The crust was crushed to the size of 2 mm and 10 mm with different cutting parameters and successfully collected by the jet pump, 6 kg in total. The crust texture was measured by the onboard sonar successfully and can be used for cutting parameter selection. The cameras captured the images of the subsea environment, but the actions of crushing and sample collection produced plumes, which blocked the camera vision. In the situation, the front image sonar can be used to keep the vehicle away from big rocks. The mining vehicle is not limited to the mining and sampling of subsea cobalt-rich crust. Most of the subsea solid resources on the seabed can be considered to use the compact mining vehicle for sampling and related research. The only issues to be considered are the crushing ability and sample size required. [ABSTRACT FROM AUTHOR]