Special Issue "Deep-Sea Minerals and Gas Hydrates"

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (31 August 2018)

Special Issue Editors

Guest Editor
Prof. Dr. Georgy Cherkashov

Institute for Geology and Mineral Resources of the Ocean, Saint Petersburg State University, Saint Petersburg, Russian Federation
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Interests: marine minerals, deep sea mineral deposits, geochemistry and mineralogy, methods of exploration, seafloor massive sulfides, evolution of hydrothermal systems
Guest Editor
Dr. Bramley Murton

National Oceanography Centre Southampton, Southampton, United Kingdom
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Special Issue Information

Dear Colleagues,

The most promising mineral resources distributed out of the shelf zones are ferromanganese nodules and crusts, seafloor massive sulfides, phosphorites and gas hydrates. Marine minerals (nodules, crusts, sulphides and phosphorites) have different characteristics in their geological setting, grades of metals and genesis. They include such commodities as Cu, Co, Ni, Mn, P, Mo, rare earth elements, Au, Ag, Pt, Te, and others. Gas hydrates considered as giant potential hydrocarbons resource.

International activities directed towards deep-ocean mining are accelerating at an amazing pace and, to date, more than 2.5 million square kilometers of the seafloor are under contract for exploration and that number is increasing monthly. Global metal markets, establishment of regulatory frameworks by coastal nations and the International Seabed Authority, and technology developments are driving this global race. Technology now exists for the mining of deep-ocean seafloor massive sulfides, manganese nodules, and phosphorite, and is in the final stages of development for cobalt-rich ferromanganese crusts. Within the next few years, the first deep-ocean mines will have begun operations and a new industry will have been born.

A special session on “Marine Mineral Resources and Impacts of Potential Mining” has been established at the Goldschmidt 2017 Conference. Articles presented at this session will also be included in the Special Issue.

Prof. Dr. Georgy Cherkashov
Dr. Bramley Murton
Guest Editors

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Keywords

  • marine minerals
  • deep-sea mineral deposits
  • submarine gas hydrates
  • ferromanganese nodules
  • co-rich manganese crusts
  • seafloor massive sulfides and low-temperature hydrothermal mineralization
  • geological setting of deep-sea mineral deposits
  • composition of deep-sea mineral deposits
  • exploration and exploitation methods
  • impact of potential mining

Published Papers (15 papers)

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Research

Open AccessArticle Numerical Simulation on Authigenic Barite Formation in Marine Sediments
Minerals 2019, 9(2), 98; https://doi.org/10.3390/min9020098
Received: 29 December 2018 / Revised: 2 February 2019 / Accepted: 5 February 2019 / Published: 10 February 2019
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Abstract
Submarine cold seep and its associated authigenic minerals in sediment are meaningful to indicate the existence of underlying natural gas hydrate. The anaerobic oxidation of methane (AOM) is coupled with sulfate reduction (SR) and influences the dissolution and precipitation of barite. However, the [...] Read more.
Submarine cold seep and its associated authigenic minerals in sediment are meaningful to indicate the existence of underlying natural gas hydrate. The anaerobic oxidation of methane (AOM) is coupled with sulfate reduction (SR) and influences the dissolution and precipitation of barite. However, the forming mechanism of barite is not yet clearly understood. In order to investigate the forming process of authigenic barite and its relationship with methane leakage flux, based on the measured data of the Qiongdongnan Basin in the Northern slope of the South China Sea, we constructed a 1D model of a sedimentary column to reproduce the formation of barite using the numerical simulation method. The results show that the original equilibrium of barite was broken by the cold seep fluids and Ba2+ was carried upward to the sulfate-rich zone leading to the formation of barite front. When there is no flux of methane from the bottom of sediment, the barite front disappears. The relationship between methane leakage flux and authigenic minerals was also discussed. It can be concluded that high methane flux corresponds to a shallow barite front in the sediment, furthermore, the barite content first increases and then decreases as the methane flux increases. At the same time, an inverse relationship between the ratio of authigenic barite to calcite and methane flux was obtained. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
Open AccessArticle Mineralogical and Geochemical Signatures of Metalliferous Sediments in Wocan-1 and Wocan-2 Hydrothermal Sites on the Carlsberg Ridge, Indian Ocean
Minerals 2019, 9(1), 26; https://doi.org/10.3390/min9010026
Received: 28 November 2018 / Revised: 25 December 2018 / Accepted: 27 December 2018 / Published: 4 January 2019
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Abstract
In this paper, we conduct a comparative study on the mineralogy and geochemistry of metalliferous sediment collected near the active hydrothermal site (Wocan-1) and inactive hydrothermal site (Wocan-2) from Wocan Hydrothermal Field, on the Carlsberg Ridge (CR), northwest Indian Ocean. We aim to [...] Read more.
In this paper, we conduct a comparative study on the mineralogy and geochemistry of metalliferous sediment collected near the active hydrothermal site (Wocan-1) and inactive hydrothermal site (Wocan-2) from Wocan Hydrothermal Field, on the Carlsberg Ridge (CR), northwest Indian Ocean. We aim to understand the spatial variations in the primary and post-depositional conditions and the intensity of hydrothermal circulations in the Wocan hydrothermal systems. Sediment samples were collected from six stations which includes TVG-07, TVG-08 (Wocan-1), TVG-05, TVG-10 (Wocan-2), TVG-12 and TVG-13 (ridge flanks). The mineralogical investigations show that sediment samples from Wocan-1 and Wocan-2 are composed of chalcopyrite, pyrite, sphalerite, barite, gypsum, amorphous silica, altered volcanic glass, Fe-oxides, and hydroxides. The ridge flank sediments are dominated by biogenic calcite and foraminifera assemblages. The bulk sediment samples of Wocan-1 have an elevated Fe/Mn ratio (up to ~1545), with lower U contents (<7.4 ppm) and U/Fe ratio (<~1.8 × 10−5). The sulfide separates (chalcopyrite, pyrite, and sphalerite) are enriched in Se, Co, As, Sb, and Pb. The calculated sphalerite precipitation temperature (Sph.PT) yields ~278 °C. The sulfur isotope (δ34S) analysis returned a light value of 3.0–3.6‰. The bulk sediment samples of Wocan-2 have a lower Fe/Mn ratio (<~523), with high U contents (up to 19.6 ppm) and U/Fe ratio (up to ~6.2 × 10−5). The sulfide separates are enriched in Zn, Cu, Tl, and Sn. The calculated Sph.PT is ~233 °C. The δ34S returned significant values of 4.1–4.3‰ and 6.4–8.7‰ in stations TVG-10 and TVG-05, respectively. The geochemical signatures (e.g., Fe/Mn and U/Fe ratio, mineral chemistry of sulfides separates, and S-isotopes and Sph.PT) suggest that sediment samples from Wocan-1 are located near intermediate–high temperature hydrothermal discharge environments. Additionally, relatively low δ34S values exhibit a lower proportion (less than 20%) of seawater-derived components. The geochemical signatures suggest that sediment samples from Wocan-2 has undergone moderate–extensive oxidation and secondary alterations by seawater in a low–intermediate temperature hydrothermal environments. Additionally, the significant δ34S values of station TVG-05 exhibit a higher estimated proportion (up to 41%) of seawater-derived components. Our results showed pervasive hydrothermal contributions into station TVG-08 relative to TVG-07, it further showed the increased process of seafloor weathering at TVG-05 relative to TVG-10. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Rare Earth Elements and Other Critical Metals in Deep Seabed Mineral Deposits: Composition and Implications for Resource Potential
Minerals 2019, 9(1), 3; https://doi.org/10.3390/min9010003
Received: 27 November 2018 / Revised: 17 December 2018 / Accepted: 17 December 2018 / Published: 21 December 2018
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Abstract
The critical metal contents of four types of seabed mineral resources, including a deep-sea sediment deposit, are evaluated as potential rare earth element (REE) resources. The deep-sea resources have relatively low total rare earth oxide (TREO) contents, a narrow range of TREO grades [...] Read more.
The critical metal contents of four types of seabed mineral resources, including a deep-sea sediment deposit, are evaluated as potential rare earth element (REE) resources. The deep-sea resources have relatively low total rare earth oxide (TREO) contents, a narrow range of TREO grades (0.049–0.185%), and show characteristics that are consistent with those of land-based ion adsorption REE deposits. The relative REO distributions of the deep-seabed resources are also consistent with those of ion adsorption REE deposits on land. REEs that are not part of a crystal lattice of host minerals within deep-sea mineral deposits are favorable for mining, as there is no requirement for crushing and/or pulverizing during ore processing. Furthermore, low concentrations of Th and U reduce the risk of adverse environmental impacts. Despite the low TREO grades of the deep-seabed mineral deposits, a significant TREO yield from polymetallic nodules and REE-bearing deep-sea sediments from the Korean tenements has been estimated (1 Mt and 8 Mt, respectively). Compared with land-based REE deposits, deep-sea mineral deposits can be considered as low-grade mineral deposits with a large tonnage. The REEs and critical metals from deep-sea mineral deposits are important by-products and co-products of the main commodities (e.g., Co and Ni), and may increase the economic feasibility of their extraction. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessFeature PaperArticle Trace Metal Distribution in Sulfide Minerals from Ultramafic-Hosted Hydrothermal Systems: Examples from the Kairei Vent Field, Central Indian Ridge
Minerals 2018, 8(11), 526; https://doi.org/10.3390/min8110526
Received: 4 September 2018 / Revised: 3 November 2018 / Accepted: 5 November 2018 / Published: 11 November 2018
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Abstract
The ultramafic-hosted Kairei vent field is located at 25°19′ S, 70°02′ E, towards the Northern end of segment 1 of the Central Indian Ridge (CIR-S1) at a water depth of ~2450 m. This study aims to investigate the distribution of trace elements among [...] Read more.
The ultramafic-hosted Kairei vent field is located at 25°19′ S, 70°02′ E, towards the Northern end of segment 1 of the Central Indian Ridge (CIR-S1) at a water depth of ~2450 m. This study aims to investigate the distribution of trace elements among sulfide minerals of differing textures and to examine the possible factors controlling the trace element distribution in those minerals using LA-ICP-MS spot and line scan analyses. Our results show that there are distinct systematic differences in trace element distributions throughout the different minerals, as follows: (1) pyrite is divided into three types at Kairei, including early-stage euhedral pyrite (py-I), sub-euhedral pyrite (py-II), and colloform pyrite (py-III). Pyrite is generally enriched with Mo, Au, As, Tl, Mn, and U. Pyrite-I has high contents of Se, Te, Bi, and Ni when compared to the other types; py-II is enriched in Au relative to py-I and py-III, but poor in Ni; py-III is enriched in Mo, Pb, and U but is poor in Se, Te, Bi, and Au relative to py-I and py-II. Variations in the concentrations of Se, Te, and Bi in pyrite are most likely governed by the strong temperature gradient. There is generally a lower concentration of nickel than Co in pyrite, indicating that our samples precipitated at high temperatures, whereas the extreme Co enrichment is likely from a magmatic heat source combined with an influence of serpentinization reactions. (2) Chalcopyrite is characterized by high concentrations of Co, Se, and Te. The abundance of Se and Te in chalcopyrite over the other minerals is interpreted to have been caused by the high solubilities of Se and Te in the chalcopyrite lattice at high temperatures. The concentrations of Sb, As, and Au are relatively low in chalcopyrite from the Kairei vent field. (3) Sphalerite from Zn-rich chimneys is characterized by high concentrations of Sn, Co, Ga, Ge, Ag, Pb, Sb, As, and Cd, but is depleted in Se, Te, Bi, Mo, Au, Ni, Tl, Mn, Ba, V, and U in comparison with the other minerals. The high concentrations of Cd and Co are likely caused by the substitution of Cd2+ and Co2+ for Zn2+ in sphalerite. A high concentration of Pb accompanied by a high Ag concentration in sphalerite indicates that Ag occurs as Pb–Ag sulfosalts. Gold is generally low in sphalerite and strongly correlates with Pb, suggesting its presence in microinclusions of galena. The strong correlation of As with Ge in sphalerite from Kairei suggests that they might precipitate at medium temperatures and under moderately reduced conditions. (4) Bornite–digenite has very low concentrations of most trace elements, except for Co, Se, and Bi. Serpentinization in ultramafic-hosted hydrothermal systems might play an important role in Au enrichment in pyrite with low As contents. Compared to felsic-hosted seafloor massive sulfide deposits, sulfide minerals from ultramafic-hosted deposits show higher concentrations of Se and Te, but lower As, Sb, and Au concentrations, the latter often attributed to the contribution of magmatic volatiles. As with typical ultramafic-hosted seafloor massive sulfide deposits, Se enrichment in chalcopyrite from Kairei indicates that the primary factor that controls the Se enrichment is temperature-controlled mobility in vent fluids. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle He–Ar–S Isotopic Compositions of Polymetallic Sulphides from Hydrothermal Vent Fields along the Ultraslow-Spreading Southwest Indian Ridge and Their Geological Implications
Minerals 2018, 8(11), 512; https://doi.org/10.3390/min8110512
Received: 28 August 2018 / Revised: 2 November 2018 / Accepted: 5 November 2018 / Published: 7 November 2018
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Abstract
Noble gases have become a powerful tool to constrain the origin and evolution of ore-forming fluids in seafloor hydrothermal systems. The aim of this study was to apply these tracers to understand the genesis of newly discovered polymetallic sulphide deposits along the ultraslow-spreading [...] Read more.
Noble gases have become a powerful tool to constrain the origin and evolution of ore-forming fluids in seafloor hydrothermal systems. The aim of this study was to apply these tracers to understand the genesis of newly discovered polymetallic sulphide deposits along the ultraslow-spreading Southwest Indian Ridge (SWIR). The helium, argon, and sulphur isotope compositions of metal sulphide minerals were measured for a number of active/inactive vent fields in the Indian Ocean. The helium concentrations and isotopic ratios in these ore samples are variable (4He: 0.09–2.42 × 10−8 cm3STP∙g−1; 3He: 0.06–3.28 × 10−13 cm3STP∙g−1; 3He/4He: 1.12–9.67 Ra) and generally greater than the modern atmosphere, but significantly lower than those in massive sulphides from the fast-spreading East Pacific Rise (EPR), especially for three Cu–Fe-rich samples from the ultramafic-hosted Tianzuo and Kairei vent fields. On the contrary, most of the SWIR sulphide deposits have somewhat higher 40Ar/36Ar ratios of trapped fluids (ranging from 290.6 to 303.4) when compared to the EPR ore samples. Moreover, the majority of sulphide minerals from the Indian Ocean have much higher δ34S values (3.0‰–9.8‰, ~5.9 on average, n = 49) than other basaltic-hosted active hydrothermal systems on the EPR. Overall, these He–Ar–S results are well within the range of seafloor massive sulphide deposits at global sediment-starved mid-ocean ridges (MORs), lying between those of air-saturated water (ASW) and mid-ocean ridge basalt (MORB) end members. Therefore, our study suggests that the helium was derived mainly from the MORB mantle by degassing during the high-temperature stage of hydrothermal activity, as well as from a mixture of vent fluids with variable amounts of ambient seawater during either earlier or late-stage low-temperature hydrothermal episodes, whereas the argon in ore-forming fluids trapped within sulphide minerals was predominantly derived from deep-sea water. Additionally, relatively high δ34S values exhibit a great estimated proportion (up to nearly 40%) of seawater-derived components. In summary, sub-seafloor extensive fluid circulation, pervasive low-temperature alteration, shallow seawater entrainment, and mixing processes, may make a larger contribution to the SWIR hydrothermal ore-forming systems, compared to fast-spreading centres. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessFeature PaperArticle Integrated Geochemical and Morphological Data Provide Insights into the Genesis of Ferromanganese Nodules
Minerals 2018, 8(11), 488; https://doi.org/10.3390/min8110488
Received: 18 September 2018 / Revised: 16 October 2018 / Accepted: 19 October 2018 / Published: 26 October 2018
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Abstract
Ferromanganese nodules grow by precipitation of metals from seawater and/or sediment pore water. The formation of different genetic types depends on the composition and redox conditions of the water and upper sediment layers, water depth, and primary productivity in surface waters. Many characteristics [...] Read more.
Ferromanganese nodules grow by precipitation of metals from seawater and/or sediment pore water. The formation of different genetic types depends on the composition and redox conditions of the water and upper sediment layers, water depth, and primary productivity in surface waters. Many characteristics of nodules have been used to investigate their genesis. In this paper, we compare nodules from different environments using Computed Tomography, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy, and Micro X-ray Fluorescence data to better understand how geochemical differences are linked to different morphological features. We use representative samples of purely hydrogenetic nodules and mixed-type nodules with various proportions of hydrogenetic and diagenetic growth laminae. Our results show a micrometric alternation between high-absorbance massive Mn-enriched (Mn/Fe up to 40) laminae and low-absorbance dendritic Mn-depleted (Mn/Fe about 1) laminae in mixed-type nodules, suggesting the rhythmic alternation of hydrogenetic oxic conditions and suboxic diagenetic input. This micro-rhythmic alternation is absent in purely hydrogenetic nodules, which are homogenous both chemically and morphologically. A conceptual model is proposed to account for these geochemical and morphological differences in terms of the vertical migration of the oxic-suboxic front relative to the base of the nodules. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Helium and Argon Isotopes in the Fe-Mn Polymetallic Crusts and Nodules from the South China Sea: Constraints on Their Genetic Sources and Origins
Minerals 2018, 8(10), 471; https://doi.org/10.3390/min8100471
Received: 17 August 2018 / Revised: 8 October 2018 / Accepted: 8 October 2018 / Published: 22 October 2018
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Abstract
In this study, the He and Ar isotope compositions were measured for the Fe-Mn polymetallic crusts and nodules from the South China Sea (SCS), using the high temperature bulk melting method and noble gases isotope mass spectrometry. The He and Ar of the [...] Read more.
In this study, the He and Ar isotope compositions were measured for the Fe-Mn polymetallic crusts and nodules from the South China Sea (SCS), using the high temperature bulk melting method and noble gases isotope mass spectrometry. The He and Ar of the SCS crusts/nodules exist mainly in the Fe-Mn mineral crystal lattice and terrigenous clastic mineral particles. The results show that the 3He concentrations and R/RA values of the SCS crusts are generally higher than those of the SCS nodules, while 4He and 40Ar concentrations of the SCS crusts are lower than those of the SCS nodules. Comparison with the Pacific crusts and nodules, the SCS Fe-Mn crusts/nodules have lower 3He concentrations and 3He/4He ratios (R/RA, 0.19 to 1.08) than those of the Pacific Fe-Mn crusts/nodules, while the 40Ar/36Ar ratios of the SCS samples are significantly higher than those of the Pacific counterparts. The relatively low 3He/4He ratios and high 40Ar concentrations in the SCS samples are likely caused by terrigenous detrital input with high radiogenic 4He and 40Ar contents. The SCS crusts and nodules have shorter growth periods, implying that in situ post-formation radiogenic 3He, 4He and 40Ar produced by decay of U, Th and K have no effect on their isotope compositions. Thus, the SCS crusts/nodules inherited the noble gases characteristics of their sources. Helium and Ar isotope compositions in the SCS Fe-Mn crusts and nodules reflect the product of an equilibrium mixture between air-saturated seawater and radiogenic components during their growth, while the partial 3He excess in some SCS samples may represent a little mantle-derived origin. The different He and Ar isotope compositions of the Fe-Mn crusts and nodules between the South China Sea and the Pacific Ocean are due to their different sources and genetic processes. The characteristics of He and Ar isotope compositions in the SCS polymetallic crusts and nodules are similar to the properties of hydrogenetic Fe-Mn oxide/hydroxide precipitates, which reflects mainly the product of an equilibrium mixture between air-saturated seawater and radiogenic components. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessFeature PaperArticle Economic Block Model Development for Mining Seafloor Massive Sulfides
Minerals 2018, 8(10), 468; https://doi.org/10.3390/min8100468
Received: 25 September 2018 / Revised: 11 October 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
To support open-pit studies related to seafloor massive sulfides mining projects, an economic block-model is required. A modular framework is proposed to produce economic block models accommodating various levels of data. The framework is illustrated on a site of interest located on the [...] Read more.
To support open-pit studies related to seafloor massive sulfides mining projects, an economic block-model is required. A modular framework is proposed to produce economic block models accommodating various levels of data. The framework is illustrated on a site of interest located on the Arctic Mid-Ocean Ridge. Random sampling based on literature datasets is performed to assign grades, porosity and grain density to the model. Other required parameters are produced using relationships found in the literature. Revenues are estimated using literature values within a net smelter return methodology. Mining costs are determined using the cost of a mining system and the estimated time required for excavating the ore. The excavating time is assessed through the specific energy for the ore and the mining machines. The specific energy is calculated with a hyperbaric rock-cutting model. An economic block value of each mining block is then provided. The mining block database resulting from the study constitutes a valuable input into further studies on resource development. The framework has also been used to support a sensitivity study. The availability of the marine assets has been found as having the greatest influence on the economic value of the study case. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessFeature PaperArticle Mineral Phase-Element Associations Based on Sequential Leaching of Ferromanganese Crusts, Amerasia Basin Arctic Ocean
Minerals 2018, 8(10), 460; https://doi.org/10.3390/min8100460
Received: 31 August 2018 / Revised: 30 September 2018 / Accepted: 7 October 2018 / Published: 17 October 2018
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Abstract
Ferromanganese (FeMn) crusts from Mendeleev Ridge, Chukchi Borderland, and Alpha Ridge, in the Amerasia Basin, Arctic Ocean, are similar based on morphology and chemical composition. The crusts are characterized by a two- to four-layered stratigraphy. The chemical composition of the Arctic crusts differs [...] Read more.
Ferromanganese (FeMn) crusts from Mendeleev Ridge, Chukchi Borderland, and Alpha Ridge, in the Amerasia Basin, Arctic Ocean, are similar based on morphology and chemical composition. The crusts are characterized by a two- to four-layered stratigraphy. The chemical composition of the Arctic crusts differs significantly from hydrogenetic crusts from elsewhere of global ocean by high mean Fe/Mn ratios, high As, Li, V, Sc, and Th concentrations, and high detrital contents. Here, we present element distributions through crust stratigraphic sections and element phase association using several complementary techniques such as SEM-EDS, LA-ICP-MS, and sequential leaching, a widely employed method of element phase association that dissolves mineral phases of different stability step-by-step: Exchangeable cations and Ca carbonates, Mn-oxides, Fe-hydroxides, and residual fraction. Sequential leaching shows that the Arctic crusts have higher contents of most elements characteristic of the aluminosilicate phase than do Pacific crusts. Elements have similar distributions between the hydrogenetic Mn and Fe phases in all the Arctic and Pacific crusts. The main host phases for the elements enriched in the Arctic crusts over Pacific crusts (Li, As, Th, and V) are the Mn-phase for Li and Fe-phase for As, Th, and V; those elements also have higher contents in the residual aluminosilicate phase. Thus, higher concentrations of Li, As, Th, and V likely occur in the dissolved and particulate phases in bottom waters where the Arctic crusts grow, which has been shown to be true for Sc, also highly enriched in the crusts. The phase distributions of elements within the crust layers is mostly consistent among the Arctic crusts, being somewhat different in element concentrations in the residual phase. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Assessment of the Mineral Resource Potential of Atlantic Ferromanganese Crusts Based on Their Growth History, Microstructure, and Texture
Minerals 2018, 8(8), 327; https://doi.org/10.3390/min8080327
Received: 4 July 2018 / Revised: 19 July 2018 / Accepted: 27 July 2018 / Published: 30 July 2018
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Abstract
The decarbonisation of our energy supply is reliant on new technologies that are raw material intensive and will require a significant increase in the production of metals to sustain them. Ferromanganese (FeMn) crusts are seafloor precipitates, enriched in metals such as cobalt and [...] Read more.
The decarbonisation of our energy supply is reliant on new technologies that are raw material intensive and will require a significant increase in the production of metals to sustain them. Ferromanganese (FeMn) crusts are seafloor precipitates, enriched in metals such as cobalt and tellurium, both of which have a predicted future demand above current production rates. In this study, we investigate the texture and composition of FeMn crusts on Tropic Seamount, a typical Atlantic guyot off the coast of western Africa, as a basis for assessing the future mineral resource potential of Atlantic Seamounts. The majority of the summit is flat and covered by FeMn crusts with average thicknesses of 3–4 cm. The crusts are characterized by two dominant textures consisting of either massive pillared growth or more chaotic, cuspate sections of FeMn oxides, with an increased proportion of detrital and organic material. The Fe, Mn, and Co contents in the FeMn oxide layers are not affected by texture. However, detrital material and bioclasts can form about 50% of cuspate areas, and the dilution effect of this entrained material considerably reduces the Fe, Mn, and Co concentrations if the bulk samples are analyzed. Whilst Tropic Seamount meets many of the prerequisites for a crust mining area, the thickness of the crusts and their average metal composition means extraction is unlikely to be viable in the near future. The ability to exploit more difficult terrains or multiple, closely spaced edifices would make economic feasibility more likely. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Sulfide Breccias from the Semenov-3 Hydrothermal Field, Mid-Atlantic Ridge: Authigenic Mineral Formation and Trace Element Pattern
Minerals 2018, 8(8), 321; https://doi.org/10.3390/min8080321
Received: 14 May 2018 / Revised: 13 July 2018 / Accepted: 23 July 2018 / Published: 27 July 2018
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Abstract
The aim of this paper is the investigation of the role of diagenesis in the transformation of clastic sulfide sediments such as sulfide breccias from the Semenov-3 hydrothermal field (Mid-Atlantic Ridge). The breccias are composed of marcasite–pyrite clasts enclosed in a barite–sulfide–quartz matrix. [...] Read more.
The aim of this paper is the investigation of the role of diagenesis in the transformation of clastic sulfide sediments such as sulfide breccias from the Semenov-3 hydrothermal field (Mid-Atlantic Ridge). The breccias are composed of marcasite–pyrite clasts enclosed in a barite–sulfide–quartz matrix. Primary hydrothermal sulfides occur as colloform, fine-crystalline, porous and radial marcasite–pyrite clasts with inclusions or individual clasts of chalcopyrite, sphalerite, pyrrhotite, bornite, barite and rock-forming minerals. Diagenetic processes are responsible for the formation of more diverse authigenic mineralization including framboidal, ovoidal and nodular pyrite, coarse-crystalline pyrite and marcasite, anhedral and reniform chalcopyrite, inclusions of HgS phase and pyrrhotite–sphalerite–chalcopyrite aggregates in coarse-crystalline pyrite, zoned bornite–chalcopyrite grains, specular and globular hematite, tabular barite and quartz. The early diagenetic ovoid pyrite is enriched in most trace elements in contrast to late diagenetic varieties. Authigenic lower-temperature chalcopyrite is depleted in trace elements relative to high-temperature hydrothermal ones. Trace elements have different modes of occurrence: Se is hosted in pyrite and chalcopyrite; Tl is related to sphalerite and galena nanoinclusions; Au is associated with galena; As in pyrite is lattice-bound, whereas in chalcopyrite it is related to tetrahedrite–tennantite nanoinclusions; Cd in pyrite is hosted in sphalerite inclusions; Cd in chalcopyrite forms its own mineral; Co and Ni are hosted in chalcopyrite. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Insights into Extinct Seafloor Massive Sulfide Mounds at the TAG, Mid-Atlantic Ridge
Minerals 2018, 8(7), 302; https://doi.org/10.3390/min8070302
Received: 15 May 2018 / Revised: 4 July 2018 / Accepted: 4 July 2018 / Published: 18 July 2018
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Abstract
Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal [...] Read more.
Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal tenor have to be fully understood. This knowledge cannot be obtained by assessing the surface exposures alone. Seafloor drilling is required to gain information about the third dimension. In 2016, three extinct seafloor massive sulfide mounds, located in the Trans-Atlantic Geotraverse (TAG) hydrothermal area of the Mid-Atlantic Ridge were drilled. A mineralogical and textural comparison of drill core and surface-grab samples revealed that in recent ceased mounds high-temperature copper assemblages typical for black smoker chimneys are still present whereas in longer extinct mounds the mineralogy is pre-dominated by an iron mineral assemblage. Zinc becomes remobilized early in the mound evolution and forms either a layer in the upper part of the mound or has been totally leached from its interior. Precipitation temperatures of sphalerite calculated using the Fe/Zn ratio can help to identify these remobilization processes. While the Fe/Zn ratios of primary sphalerites yield temperatures that are in very good agreement with fluid temperatures measured in white smokers, calculated temperatures for sphalerites affected by remobilization are too high for SMS. Overall drilling of SMS provides valuable information on the internal structure and mineralogy of the shallow sub-surface, however, additional drilling of SMS, at a greater depth, is required to fully understand the processes affecting SMS and their economic potential. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle High-Resolution Analysis of Critical Minerals and Elements in Fe–Mn Crusts from the Canary Island Seamount Province (Atlantic Ocean)
Minerals 2018, 8(7), 285; https://doi.org/10.3390/min8070285
Received: 28 May 2018 / Revised: 25 June 2018 / Accepted: 27 June 2018 / Published: 2 July 2018
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Abstract
Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of [...] Read more.
Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of distinguishing the critical elements and their association with mineral phases and genetic processes forming a long-lived Fe–Mn crust. The Fe–Mn crust collected on the Tropic Seamount is composed of dense laminations of Fe-vernadite (>90%) and goethite group minerals, reflecting the predominance of the hydrogenetic process during their formation. Based on high-resolution age calculation, this purely hydrogenetic crust yielded an age of 99 Ma. The Fe–Mn crust collected on the Paps Seamount shows a typical botryoidal surface yielding an age of 30 Ma. electron probe microanalyzer (EPMA) spot analyses show two main types of manganese oxides, indicating their origin: (i) hydrogenetic Fe-vernadite, the main Mn oxide, and (ii) laminations of interlayered buserite and asbolane. Additionally, the occurrence of calcite, authigenic carbonate fluor-apatite (CFA) and palygorskite suggests early diagenesis and pervasive phosphatization events. Sequential leaching analysis indicated that Co, Ni, Cu, Ba and Ce are linked to Mn minerals. Therefore, Mn-oxides are enriched in Ni and Cu by diagenetic processes or in Co and Ce by hydrogenetic processes. On the other hand, Fe-oxides concentrate V, Zn, As and Pb. Moreover, the evidence of HREE enrichment related to Fe-hydroxides is confirmed in the mixed hydrogenetic/diagenetic crust. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Accumulation of Platinum Group Elements in Hydrogenous Fe–Mn Crust and Nodules from the Southern Atlantic Ocean
Minerals 2018, 8(7), 275; https://doi.org/10.3390/min8070275
Received: 27 May 2018 / Revised: 22 June 2018 / Accepted: 25 June 2018 / Published: 28 June 2018
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Abstract
Distribution of platinum group elements (Ru, Pd, Pt, and Ir) and gold in hydrogenous ferromanganese deposits from the southern part of the Atlantic Ocean has been studied. The presented samples were the surface and buried Fe–Mn hydrogenous nodules, biomorphous nodules containing predatory fish [...] Read more.
Distribution of platinum group elements (Ru, Pd, Pt, and Ir) and gold in hydrogenous ferromanganese deposits from the southern part of the Atlantic Ocean has been studied. The presented samples were the surface and buried Fe–Mn hydrogenous nodules, biomorphous nodules containing predatory fish teeth in their nuclei, and crusts. Platinum content varied from 47 to 247 ng/g, Ru from 5 to 26 ng/g, Pd from 1.1 to 2.8 ng/g, Ir from 1.2 to 4.6 ng/g, and Au from less than 0.2 to 1.2 ng/g. In the studied Fe–Mn crusts and nodules, Pt, Ir, and Ru are significantly correlated with some redox-sensitive trace metals (Co, Ce, and Tl). Similar to cobalt and cerium behaviour, ruthenium, platinum, and iridium are scavenged from seawater by suspended ferromanganese oxyhydroxides. The most likely mechanism of Platinum Group Elements (PGE) accumulation can be sorption and oxidation on δ-MnO2 surfaces. The obtained platinum fluxes to ferromanganese crusts and to nodules are close and vary from 35 to 65 ng∙cm−2∙Ma−1. Palladium and gold do not accumulate in hydrogenous ferromanganese deposits relative to the Earth’s crust. No correlation of Pd and Au content with major and trace elements in nodules and crusts have been identified. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Open AccessArticle Linkages between the Genesis and Resource Potential of Ferromanganese Deposits in the Atlantic, Pacific, and Arctic Oceans
Minerals 2018, 8(5), 197; https://doi.org/10.3390/min8050197
Received: 6 March 2018 / Revised: 26 April 2018 / Accepted: 3 May 2018 / Published: 5 May 2018
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Abstract
In addition to iron and manganese, deep sea ferromanganese deposits, including nodules and crusts, contain significant amounts of economically interesting metals, such as cobalt (Co), nickel (Ni), copper (Cu), and rare Earth elements and yttrium (REY). Some of these metals are essential in [...] Read more.
In addition to iron and manganese, deep sea ferromanganese deposits, including nodules and crusts, contain significant amounts of economically interesting metals, such as cobalt (Co), nickel (Ni), copper (Cu), and rare Earth elements and yttrium (REY). Some of these metals are essential in the development of emerging and new-generation green technologies. However, the resource potential of these deposits is variable, and likely related to environmental conditions that prevail as they form. To better assess the environmental controls on the resource potential of ferromanganese deposits, we have undertaken a detailed study of the chemical composition of ferromanganese nodules and one crust sample from different oceanic regions. Textural and chemical characteristics of nodules from the North Atlantic and a crust from the South Pacific suggest that they acquire metals from a hydrogenous source. These deposits are potentially an economically important source of Co and the REY. On the other hand, nodules from the Pacific Ocean represent a marginal resource of these metals, due to their relatively fast growth rate caused by diagenetic precipitation. By contrast, they have relatively high concentrations of Ni and Cu. A nodule from the Arctic Ocean is characterised by the presence of significant quantities of detrital silicate material, which significantly reduces their metal resource. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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