Deep Sea Research Part I: Oceanographic Research Papers
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Cobalt-rich ferromanganese crusts on seamounts have attracted much attention due to high economic potential of various metals. Studies showed that seamounts in the Western Pacific Ocean are rich in cobalt-rich crusts, and Weijia Guyot (Ita Mai Tai) is one of the most promising one. Cobalt-rich crusts were drilled from this seamount in our previous investigation. This study evaluates promising areas of cobalt-rich crusts on the whole guyot. Combined the sub-bottom profiles, topography, scientific ocean drilling data with related studies, this paper studied sedimentary characteristic and their implications for cobalt-rich crusts mineralization prospective areas on the summit of Weijia Guyot. Three types of stratum reflection characteristics were identified: pelagic deposits, oolitic limestone, and lagoonal mud. Reflection sequences in Chirp sub-bottom profiler records are well matched to stratigraphy obtained at Deep-Sea Drilling Project Sites 200 and 202. Cobalt-rich crusts promising mineralization areas were delineated based on the water depth, slope gradient and pelagic pinch-out line, with the area approximately 576.4 km2. This estimated number is 10% higher than the results from previous studies (approximately 436.6 km2). It provides great implication for exploration and mining-lease-block selection in the future.
As cobalt-rich ferromanganese crusts (short for cobalt-rich crusts) constitute important submarine solid mineral, a series of investigations and studies have been carried out since the 1980s (Craig et al., 1982; Halbach and Manheim, 1984; Halbach et al., 1987; Glasby et al., 1987; Yamazaki, 1993; Yamazaki et al., 1996; Yamazaki and Sharma, 1998; Verlaan et al., 2004; Hein et al., 2009; Asavin et al., 2010; He et al., 2011; Du et al., 2017; Zhao et al., 2019a). Previous studies have indicated that cobalt-rich crusts occur on sediment-free surfaces of seamount slopes and summits. Crusts generate growing economic interest owing to potential of metal production, including manganese, cobalt, nickel, rare earth elements (REE), tellurium and platinum group elements (PGE)(Hein et al., 2000; Hein, 2000; Verlaan et al., 2004). To identify promising areas of mining exploration, it is vital to delineate zones of the highest abundance of cobalt-rich crusts in surveyed regions.
The mineralization and distribution of crusts are influenced by multiple ore-controlling parameters. Several evidence show a relationship between the coverage of cobalt-rich crusts/nodules and slope gradients of seamounts in the Pacific Ocean (Yamazaki and Sharma, 1998). Cobalt-rich crusts are enriched in areas where the slope gradients are greater than 15°, and coexist with sediments when the gradients are between 4° and 15°, according to photo and video evidence. Ma et al. (2014) indicated that low slope gradients (3–7°) contribute to the mineralization of crusts: as the slope increases, the thickness of crusts gradually decreases, according to submarine dredging, photos, videos, and gradient data from central Pacific Ocean seamounts. Kim et al. (2013) and Yang et al. (2016a) analyzed the correlation between photos, videos and geological sampling data with acoustic backscatter data, and concluded that acoustic backscatter results can be used to determine the regional spatial distribution of cobalt-rich crusts. However, similar backscatter intensity characteristics may implicate different surficial deposits. Geological prospecting investigations carried out by Russian scientists in the eastern segment of the Magellan Seamounts during the cruise of the R/V Gelendzhik in 2003–2010 (Mel'nikov et al., 2010, 2012), Asavin et al. (2010) and Novikov et al. (2014) attempted to delineate the most promising seamount areas for future mining by use of geo-acoustic studies, shallow drillings, and sampling of cobalt-rich crusts.
He et al. (2005a) and Zhao et al., 2019a explained interconnections between sub-bottom profiling and deep-sea video recordings in Western Pacific seamounts. They found the crust distribution can be revealed by synchronous application of sub-bottom profiling and video recordings. The lower boundary of the sediments corresponds with the upper boundary of crusts. Summarizing, the slope gradients, water depths, seafloor topography, sediments distribution and other parameters are main factors which control the distribution of mineral resources on seamounts. Several detailed research attempt to find the best method to delineate areas prospective with cobalt-rich crusts on seamounts.
Different studies shown the spire seamounts indicate higher crust abundances and coverage, than guyots (Chu et al., 2006). However, restricted by the limitations of current mining technology, mining operations focus on the summit region of guyots, ridges, and plateaus on flat or shallowly inclined surfaces, such as summit terraces, platforms, and saddles, which show relatively smooth small scale changes with topography (Hein et al., 2000; Hein, 2000).
The cobalt-rich crusts which are widely developed on the surface of guyots in the Pacific Ocean have been studied for more than half a century (Asavin et al., 2010). The investigation of cobalt-rich crusts in China started around 1997 and has been carried out by more than twenty expeditions in the Central Pacific and Western Pacific seamounts. The Weijia Guyot (Ita Mai Tai) studied in this paper is one of these seamounts (He et al., 2001, 2005a; 2005b; Yang et al., 2016b; Wei et al., 2017; Hein et al., 2009; Zhao et al., 2019a).
The Weijia Guyot was drilled, dated, and surveyed with gravity, seismics, sub-bottom profiling, and magnetic methods (Heezen et al., 1973; Heezen and MacGregor, 1973; Koppers et al., 1998; Asavin et al., 2010; Lee et al., 2003, 2005). Geochemical composition of cobalt-rich ferromanganese crusts from Weijia Guyot contains mainly oxides of Mn (up to 22.9wt%), Fe (up to 21.4wt%), S (up to 0.42wt%), Co (up to 8960ppm), Ni, Cu, Zn, REE, Mo, Pt, and other trace and rare elements (Asavin et al., 2010; Wang et al., 2017). In addition, REE and PGE are found rich on the southern and southwestern slopes (Wang et al., 2017). Geological sampling and geophysical surveys undertaken by China Ocean Mineral Resource R&D Association has revealed the central summit of the Weijia Guyot is constituted of covered by calcareous pelagic oozes, while carbonate sediments cover the edges (Yang et al., 2016b; Wei et al., 2017; Wang et al., 2017).
As any of previous research identified the cobalt-rich crusts from Weijia Guyot as a metallogenically prospective, we analyzed high precision topographic data, sub-bottom profiles and archival materials and publications, for purpose of detailed sedimentary characteristics of guyot summits. The paper focus on architecture of sediments and deals with implications for exploration and mining-lease-block selection at Weijia Guyot.
The Weijia Guyot is located at the southern end of the Magellan Seamounts, in the Western Pacific Ocean (Fig. 1a). The Magellan Seamounts are adjacent to the Mariana Trench and East Mariana Basin (EMB) to the west and southwest, respectively. The Malkuswick Islands are located north and Marshall Islands southeast to the guyot (Fig. 1a). An L-shaped flank ridge extends west and south. The area of Weijia Guyot summit is approximately 1459.7km2. Plateau elevations are generally situated at depths
Data and methods
Sub-bottom profiling serve as an invaluable technology to study the depositional and erosional processes in deep-sea environments (Lee et al., 2002; Zhao et al., 2018). In marine geological survey, sub-bottom profiling can effectively identify pelagic sediments, basement outcrops, slide deposits and debris zones (He et al., 2005a; Lee et al., 2005; Mel'nikov et al., 2010; Zhao et al., 2019a).
Sub-bottom profiles and seabed bathymetry data used in this study were collected by the R/V “
Stratum reflection characteristics
Two sub-bottom profiles were selected for reflection characteristics analysis: line DY41SP1610, which passes through the DSDP20-200, and DY41SP1605 crossing the northwest of DSDP20-202 (Figs. 1b and 3). Stratum reflection of Weijia Guyot were divided into three types. Type I indicates sharp reflections of parallel layers and non-distracted horizontal continuity, extending from the center of the seamount till the edges, where sediments pinch-out (Fig. 3, Fig. 4). Type II, below Type I, exhibits
Cobalt-rich ferromanganese crusts are oxides and (oxy)hydroxides formed on the surfaces of submarine rocks or debris. Crusts are mainly distributed on guyots or top and slope of marine terraces above the carbonate compensation depth (CCD). Crusts form within the Oxygen Minimum Zone (OMZ) or below the OMZ, with depths between 500m and 3500m, especially enriched in the depth of 800–2500m (Halbach and Manheim, 1984; Halbach et al., 1987; Glasby et al., 1987; Hein et al., 2013).
Based on a sub-bottom profiles and topographic data, combined with the DSDP lithological data and related studies, this paper provide sedimentary characteristics and implications for mineralization of cobalt-rich ferromanganese crusts, on the summit of Weijia Guyot, Western Pacific Ocean.
Three types of stratum reflections are identified: (1) pelagic oozes, (2) oolitic limestones, and (3) mudstones, matching properly with DSDP coring results. Calculation results revealed that the sedimentary
Bin Zhao performed preliminary thoughts, data processing, interpretation and then wrote the main manuscript text; Yong Yang and Zhenquan Wei provided geological data, involved in geological interpretation and part of the text work; Xiangyu Zhang and Ning Huang prepared the figures in this article; Gaowen He and Wenchao Lü provided preliminary thoughts and manuscript review; Yinan Deng responsible for part of the text work; and Yuping Liu provided RadExPro software training. All authors reviewed
Declaration of competing interest
No potential conflict of interest was reported by the authors.
Thanks for the support for all of the expedition members of R/V “Haiyangliuhao” (GMGS). Thanks to Professor Weilin Ma from the Second Institute of Oceanography of Ministry of Natural Resources, for his valuable suggestions. Thanks to Doctor Neil Mitchell from University of Manchester, and three other anonymous reviewers, for their rigorous and scientific comments and suggestions on the manuscript. Thanks for the financial support from National Natural Science Foundation of China (No. 41606071
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Cobalt-rich ferromanganese crusts: global distribution, composition,origin and research activities
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Microstratigraphic evidence of oceanographic and tectonic controls on hydrogenetic ferromanganese crusts in the NW Pacific seamounts
2023, Marine Geology
Selected hydrogenetic ferromanganese crusts were characterized at a microstratigraphic scale across various NW Pacific seamounts. The crusts encompassed over 100 sites, and were mostly found on old rock outcrops. The crusts also exhibit spatial compositional variation and are largely enriched in Co and Ni. However, the parameters controlling this compositional variation remain unclear. To address this issue, we characterized the microstructure, mineralogical and chemical compositions of seven carefully selected samples from topographic highs in the mid-latitudes on the Philippine Sea and Pacific plates and revealed the following trends: (1) the lower phosphatized layer formed in the middle Miocene or earlier and only on the Pacific Plate, (2) an increasing Co/Mn ratio with younger age from the substrate to the surface, and generally higher in the Pacific Plate than the Philippine Sea Plate, and (3) an increase of detrital quartz and plagioclase since approximately 5Ma, with high Al/Mn ratios near the continental margin and to a lesser extent in pelagic areas. These results are partly congruent with those of other sediment cores from the other NW Pacific basins. Furthermore, the secular increase of Co and detrital minerals in the crust samples suggests a strong influence of oceanographic and tectonic conditions, especially the expansion of the oxygen minimum zone (OMZ) for the former and a significant input of detrital materials from the continents for the latter.
A possible link between seamount sector collapse and manganese nodule occurrence in the abyssal plains, NW Pacific Ocean
2021, Ore Geology Reviews
Citation Excerpt :
Most guyot summits are covered by ferromanganese crusts, with or without areas of thin layer of sediments due to the influence of strong bottom current. By contrast, the summit of the Magellan guyots are covered by reef limestone overlain by calcareous pelagic sediments that combined measure up to 180 m thick on Caiwei guyot, with ferromanganese crusts occurring around the periphery of the summit platform (Zhao et al., 2020a; Zhao et al., 2020b). Many guyots, such as Caiwei and Weijia (Fig. 1), have collapsed flanks and landslide topography, manifested by amphitheater-shaped headwalls on the upper flank, linear debris ridges and troughs along the middle flank, and a debris apron covering the lower flank (Yang et al., 2020; Zhao et al., 2020a; Zhao et al., 2020b).
Manganese nodules are a potential source of critical metals such as Cu, Ni, and Co and are widely distributed on the abyssal plains of the global oceans. A polymetallic nodule metallogenic belt with a heterogeneous and spatially clustered nodule distribution was recently discovered in NW Pacific inter-seamount basin (NPIB) areas. However, the geological processes that regulate the nodule occurrence in that region are unresolved. Here, we report on the characteristics of a high-density field of manganese nodules in the abyssal plain north of Suda Seamount. Ship-borne multibeam bathymetric data reveal a typical seamount sector-collapse topography characterized by radial lineaments of debris channels and ridges formed by rapid debris-avalanche flow. Backscatter data linked with underwater observation indicate that manganese nodules are more concentrated (50%–80% areal coverage) along the main body of the debris apron compared to adjacent neighboring areas (<30%). The extremely high concentrations (~80% areal coverage) characterized by overlapping nodules are apparently associated with downslope movement, possibly triggered by block movement along the fault slip plane or by gravity processes. Our results indicate that seamount sector collapse may have provided sufficient nucleus material for nodule growth and contributed to high nodule concentrations locally. The destruction of submarine volcanic edifices is universal, and the debris aprons and plains around such seamounts are potential prospecting areas for manganese nodule resources throughout the NPIB.
Enhancing the Coverage of Underwater Robot Based Mn-crust Survey Area by Using a Multibeam Sonar
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Separation of Cu, Co, Ni and Mn from acid leaching solution of ocean cobalt-rich crust using precipitation with Na<inf>2</inf>S and solvent extraction with N235
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Controls on ferromanganese crust composition and reconnaissance resource potential, Ninetyeast Ridge, Indian Ocean
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A reconnaissance survey of Fe–Mn crusts from the 5000km long (~31°S to 10°N) Ninetyeast Ridge (NER) in the Indian Ocean shows their widespread occurrence along the ridge as well as with water depth on the ridge flanks. The crusts are hydrogenetic based in growth rates and discrimination plots. Twenty samples from 12 crusts from 9 locations along the ridge were analyzed for chemical and mineralogical compositions, growth rates, and statistical relationships (Q-mode factor analysis, correlation coefficients) were calculated. The crusts collected are relatively thin (maximum 40mm), and those analyzed varied from 4mm to 32mm. However, crusts as thick as 80mm can be expected to occur based on the age of rocks that comprise the NER and the growth rates calculated here. Growth rates of the crusts increase to the north along the NER and with water depth. The increase to the north resulted from an increased supply of Mn from the oxygen minimum zone (OMZ) to depths below the OMZ combined with an increased supply of Fe at depth from the dissolution of biogenic carbonate and from deep-sourced hydrothermal Fe. These increased supplies of Fe increased growth rates of the deeper-water crusts along the entire NER. Because of the huge terrigenous (rivers, eolian, pyroclastic) and hydrothermal (three spreading centers) inputs to the Indian Ocean, and the history of primary productivity, Fe–Mn crust compositions vary from those analyzed from open-ocean locations in the Pacific.
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Fe–Mn crusts from a dredge haul at 3412m water depth, 2°S latitude, are pervasively phosphatized along with the substrate rocks (site D7). Phosphatization took place through replacement of carbonate, preferential replacement of Fe oxyhydroxide relative to Mn oxide in the crusts, preferential replacement of silica-rich phases relative to Al-rich phases in the crusts, and precipitation of carbonate fluorapatite in pore space. The preferentially replaced silica may have been Si adsorbed on the Fe oxyhydroxide. The enrichment of Ni, Zn, and Cu in the phosphatized crust reflects preferential adsorption into the tunnel structure of todorokite. The rare earth element plus yttrium (REY) patterns indicate a lower oxidation potential during phosphatization of the NER crusts compared to Pacific phosphatized crusts. NER phosphatization occurred in a deeper-water environment than typical for phosphatization of Pacific crusts, occurred post-middle Miocene, a younger age than phosphatization the Pacific crusts, and had in part a different set of chemical changes produced by the phosphatization than did the Pacific crusts.
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The influence of suboxic diagenesis on the formation of manganese nodules in the Clarion Clipperton nodule belt of the Pacific Ocean
Marine Geology, Volume 357, 2014, pp. 123-138
Polymetallic nodules and a single Fe-Mn crust from the Clarion and Clipperton Zone (CCZ) of the equatorial eastern Pacific have been analyzed to determine their chemical and mineralogical compositions. ICP-OES analyses of bulk nodules from the CCZ indicate that the nodules formed under oxic-diagenetic conditions with typical Mn/Fe ratios of 4–6, Ni+Cu values of 2–3wt.%, Co contents of 0.12–0.17wt.%. However, detail analyses of individual growth layers by electron microprobe analyses (EMPA) reveal much larger chemical heterogeneity of individual layers with Mn/Fe ratios ranging from <1 to >800. Two different genetic types of layers can be distinguished:
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Mixed layer type 3: These layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm-thin layers of low or high reflectivity. The Mn/Fe ratios of this material range between 3 and 11, Ni+Cu of 1–4.6wt.%, and Co contents are between 0.02 and 0.77wt.%. In most cases these growth structures represent a mixture of type 1 and 2 layers.
X-ray photoelectron spectroscopy (XPS) of the recent outermost nm layers of nodules (top, rim and bottom side) indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water. The mixed-type CCZ nodules are interpreted to consist of an oxic-hydrogenetic and a suboxic-diagenetic end member. Calculations of the proportions of the individual layer end members show that suboxic layers make up about 50–60% of the chemical inventory of the CCZ nodules whereas oxic-hydrogenetic layers comprise about 35–40%. The remaining part (5–10%) consists of incorporated sediment particles occurring along cracks and pores.
These results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern CCZ. This is probably due to fluctuating bioproductivity in the equatorial Pacific surface waters during glacial–interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments. Furthermore, reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near-surface sediments.
Our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation.
Late Cretaceous and Cenozoic paleoceanography from north-east Atlantic ferromanganese crust microstratigraphy
Marine Geology, Volume 422, 2020, Article 106122
Oceanic hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from ambient seawater over millions of years. Their very slow growth rates and physio-chemical properties mean that they adsorb numerous elements from seawater. As such, they provide condensed records of seawater evolution through time that can be used for paleoceanographic reconstruction. Here, we present the results of a high-resolution, stratigraphic, textural and geochemical investigation of a core sample, obtained from a Fe-Mn crust pavement, located on the summit of Tropic Seamount in the tropical north-east Atlantic Ocean. A number of observations and interpretations are proposed, within the context of a well-constrained age model, spanning the last 75±2Myr. This core has textural stratigraphic coherence with Pacific Fe-Mn crusts formed since the Late Cretaceous, highlighting that global oceanic and climatic phenomena exert first-order controls on Fe-Mn crust development. All major hiatuses observed in the Fe-Mn crusts are contemporaneous with erosion events occurring throughout the Atlantic Ocean. High-resolution geochemical data indicate that there is variability in the composition of Fe-Mn crusts at the cm to μm scale. The dominant factors controlling this include major oceanographic events, mineral textures and micro-topography.
High-accuracy acoustic sediment classification using sub-bottom profile data
Estuarine, Coastal and Shelf Science, Volume 265, 2022, Article 107701
Sub-bottom sediment classifications have been widely used in marine science and engineering to obtain high-resolution information on types of sediments; however, these are often plagued by inaccuracies. Classification difficulties arise from the inability to effectively filter multiple reflections, extract representative lithology characteristic parameters, identify sub-bottom layer interfaces, extract image samples, control sample quality, optimise characteristic parameters, etc. To generate a highly accurate sub-bottom profile sediment map, a five-step classification method that considers two key lithology characteristic parameters of sub-bottom profile acoustic data was proposed. First, multiple reflections were filtered from the sea surface and sub-bottom layer interfaces of the primary signal. Second, two key characteristic parameters (relative backscattering intensity difference and attenuation compensation residual) were calculated. These reflect the relative differences in backscattering intensity and the attenuation compensation between adjacent interfaces based on the sound intensity attenuation model of a sub-bottom profile. Third, a combined method based on the sediment quality factor and peak trough of the echo signal loss level curve was employed to identify the actual interfaces between layers. An additional technique was proposed to determine the image sample width and preferred characteristic parameters. The resulting high-quality image samples and preferred characteristic parameters not only resulted in a faster convergence rate and increased ability of self-aggregation and identification, but also ensured that the training results met the convergence accuracy requirement. Ultimately, the preferred image samples were trained to classify the overall sub-bottom map of a selected test area of approximately 36km2 in Bahai Bay, China. Compared with traditional methods, a considerably higher sediment identification accuracy was obtained. The experimental results indicate that the contribution rate of the two key lithology characteristic parameters was 65.49% according to principal component analysis, and the internal and external compatibilities were 97.98% and 84.76% for the training image samples, respectively. The total identification accuracy for the sub-bottom profile map was 98.2%. The two key characteristic parameters accurately captured the acoustic characteristics of sub-bottom sediments, significantly improving sediment classification. These results show that this method could be used to help refine the distributional estimates of submarine mineral resources.
Formation of Fe-Mn crusts within a continental margin environment
Ore Geology Reviews, Volume 87, 2017, pp. 25-40
This study examines Fe-Mn crusts that form on seamounts along the California continental-margin (CCM), within the United States 200 nautical mile exclusive economic zone. The study area extends from approximately 30° to 38° North latitudes and from 117° to 126° West longitudes. The area of study is a tectonically active northeast Pacific plate boundary region and is also part of the North Pacific Subtropical Gyre with currents dominated by the California Current System. Upwelling of nutrient-rich water results in high primary productivity that produces a pronounced oxygen minimum zone. Hydrogenetic Fe-Mn crusts forming along the CCM show distinct chemical and mineral compositions compared to open-ocean crusts. On average, CCM crusts contain more Fe relative to Mn than open-ocean Pacific crusts. The continental shelf and slope release both Fe and Mn under low-oxygen conditions. Silica is also enriched relative to Al compared to open-ocean crusts. This is due to the North Pacific silica plume and enrichment of Si along the path of deep-water circulation, resulting in Si enrichment in bottom and intermediate waters of the eastern Pacific.
The CCM Fe-Mn crusts have a higher percentage of birnessite than open-ocean crusts, reflecting lower dissolved seawater oxygen that results from the intense coastal upwelling and proximity to zones of continental slope pore-water anoxia. Carbonate fluorapatite (CFA) is not present and CCM crusts do not show evidence of phosphatization, even in the older sections. The mineralogy indicates a suboxic environment under which birnessite forms, but in which pH is not high enough to facilitate CFA deposition. Growth rates of CCM crusts generally increase with increasing water depth, likely due to deep-water Fe sources mobilized from reduced shelf and slope sediments.
Many elements of economic interest including Mn, Co, Ni, Cu, W, and Te have slightly or significantly lower concentrations in CCM crusts relative to crusts from the Pacific Prime Crust Zone and other open-ocean basins. However, concentrations of total rare earth elements and yttrium average only slightly lower contents and in the future may be a strategic resource for the U.S.
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