Manganese nodule


Polymetallic nodules, also called manganese nodules, are mineral concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core. As nodules can be found in vast quantities, and contain valuable metals, deposits have been identified as a potential economic interest.[1]

Manganese nodule
Nodules on the seabed

Nodules vary in size from tiny particles visible only under a microscope to large pellets more than 20 centimetres (8 in) across. However, most nodules are between 3 and 10 cm (1 and 4 in) in diameter, about the size of hen's eggs or potatoes. Their surface textures vary from smooth to rough. They frequently have botryoidal (mammillated or knobby) texture and vary from spherical in shape to typically oblate (flying saucer), sometimes prolate (Rugby ball), or are otherwise irregular. The bottom surface, buried in sediment, is generally rougher than the top due to a different type of growth.[2]


Nodules lie on the seabed sediment, often partly or completely buried. They vary greatly in abundance, in some cases touching one another and covering more than 70% of the sea floor surface. The total amount of polymetallic nodules on the sea floor was estimated at 500 billion tons by Alan A. Archer of the London Geological Museum in 1981.[citation needed]

Polymetallic nodules are found in both shallow (e.g. the Baltic Sea[3]) and deeper waters (e.g. the central Pacific), even in lakes,[citation needed][4] and are thought to have been a feature of the seas and oceans at least since the deep oceans oxidised in the Ediacaran period over 540 million years ago.[5]

Polymetallic nodules were discovered in 1868 in the Kara Sea, in the Arctic Ocean of Siberia. During the scientific expeditions of HMS Challenger (1872–1876), they were found to occur in most oceans of the world.[6]

Their composition varies by location, and sizeable deposits have been found in the following areas:

The largest of these deposits in terms of nodule abundance and metal concentration occur in the Clarion Clipperton Zone on vast abyssal plains in the deep ocean between 4,000 and 6,000 m (13,000 and 20,000 ft). The International Seabed Authority estimates that the total amount of nodules in the Clarion Clipperton Zone exceeds 21 billions of tons (Bt), containing about 5.95 Bt of manganese, 0.27 Bt of nickel, 0.23 Bt of copper and 0.05 Bt of cobalt.[2]

All of these deposits are in international waters apart from the Penrhyn Basin, which lies within the exclusive economic zone of the Cook Islands.

Growth and composition

Manganese nodules from the South Pacific Ocean

On the seabed the abundance of nodules varies and is likely controlled by the thickness and stability of a geochemically active layer that forms at the seabed.[11] Pelagic sediment type and seabed bathymetry (or geomorphology) likely influence the characteristics of the geochemically active layer.

Nodule growth is one of the slowest of all known geological phenomena, on the order of a centimeter over several million years.[12] Several processes are hypothesized to be involved in the formation of nodules, including the precipitation of metals from seawater, the remobilization of manganese in the water column (diagenetic), the derivation of metals from hot springs associated with volcanic activity (hydrothermal), the decomposition of basaltic debris by seawater (halmyrolitic) and the precipitation of metal hydroxides through the activity of microorganisms (biogenic).[13] The sorption of divalent cations such as Mn2+, Fe2+, Co2+, Ni2+, and Cu2+ at the surface of Mn- and Fe-oxyhydroxides, known to be strong sorbents, also plays a main role in the accumulation of these transition metals in the manganese nodules. These processes (precipitation, sorption, surface complexation, surface precipitation, incorporation by formation of solid solutions...) may operate concurrently or they may follow one another during the formation of a nodule.

Manganese nodules are essentially composed of hydrated phyllomanganates. These are layered Mn-oxide minerals with interlayers containing water molecules in variable quantities. They strongly interact with trace metals (Co2+, Ni2+) because of the octahedral vacancies present in their layers. The particular properties of phyllomanganates explain the role they play in many geochemical concentration processes. They incorporate traces of transition metals mainly via cation exchange[14] in their interlayer like clay minerals and surface complexation[15] by formation of inner sphere complexes at the oxide surface as it is also the case with hydrous ferric oxides, HFO.[16] Slight variations in their crystallographic structure and mineralogical composition may result in considerable changes in their chemical reactivity.[17]

Polymetallic nodules

The mineral composition of manganese-bearing minerals is dependent on how the nodules are formed; sedimentary nodules, which have a lower Mn2+ content than diagenetic, are dominated by Fe-vernadite, Mn-feroxyhyte, and asbolane-buserite while diagenetic nodules are dominated by buserite I, birnessite, todorokite, and asbolane-buserite.[14] The growth types termed diagenetic and hydrogenetic reflect suboxic and oxic growth, which in turn could relate to periods of interglacial and glacial climate. It has been estimated that suboxic-diagenetic type 2 layers make up about 50–60% of the chemical inventory of the nodules from the Clarion Clipperton Zone (CCZ) whereas oxic-hydrogenetic type 1 layers comprise about 35–40%. The remaining part (5–10%) of the nodules consists of incorporated sediment particles occurring along cracks and pores.[18]

The chemical composition of nodules varies according to the type of manganese minerals and the size and characteristics of their core. Those of greatest economic interest contain manganese (27–30 wt. %), nickel (1.25–1.5 wt. %), copper (1–1.4 wt. %) and cobalt (0.2–0.25 wt. %). Other constituents include iron (6 wt. %), silicon (5 wt. %) and aluminium (3 wt. %), with lesser amounts of calcium, sodium, magnesium, potassium, titanium and barium, along with hydrogen and oxygen as well as water of crystallization and free water.

A wide range of trace elements and trace minerals are found in nodules with many of these incorporated from the seabed sediment, which itself includes particles carried as dust from all over the planet before settling to the seabed.[2]

Proposed mining

Interest in the potential exploitation of polymetallic nodules generated a great deal of activity among prospective mining consortia in the 1960s and 1970s. Almost half a billion dollars was invested in identifying potential deposits and in research and development of technology for mining and processing nodules. These initial undertakings were carried out primarily by four multinational consortia composed of companies from the United States, Canada, the United Kingdom, West Germany, Belgium, the Netherlands, Italy, Japan, and two groups of private companies and agencies from France and Japan. There were also three publicly sponsored entities from the Soviet Union, India and China.

In the late 1970s, two of the international joint ventures collected several hundred-ton quantities of manganese nodules from the abyssal plains (18,000 feet (5.5 km) + depth) of the eastern equatorial Pacific Ocean.[11] Significant quantities of nickel (the primary target) as well as copper and cobalt were subsequently extracted from this "ore" using both pyrometallurgical and hydrometallurgical methods. In the course of these projects, a number of ancillary developments evolved, including the use of near-bottom towed side-scan sonar array to assay the nodule population density on the abyssal silt while simultaneously performing a sub-bottom profile with a derived, vertically oriented, low-frequency acoustic beam.[citation needed]

The technology and experience developed during the course of this project were never commercialized because the last two decades of the 20th century saw an excess of nickel production. The estimated $3.5-billion (1978 US dollars) investment to implement commercialization was an additional factor. Sumitomo Metal Mining continues to maintain a small (place-keeping) organization in this field.[citation needed]

Kennecott Copper had explored the potential profits in manganese nodule mining and found that it was not worth the cost. On top of the environmental issues and the fact that the profits had to be shared, there was no cheap way to get the manganese nodules off the sea floor.[citation needed]

Since the late 1970s, deep sea technology has improved significantly: including widespread and low cost use of navigation technology such as Global Positioning System (GPS) and ultra-short baseline (USBL); survey technology such as multibeam echosounder (MBES) and autonomous underwater vehicles (AUV); and intervention technology including remotely operated underwater vehicle (ROV) and high power umbilical cables. There is also improved technology that could be used in mining including pumps, tracked and screw drive rovers, rigid and flexible drilling risers, and ultra-high-molecular-weight polyethylene rope. Mining is considered to be similar to the potato harvest on land, which involves mining a field partitioned into long, narrow strips. The mining support vessel follows the mining route of the seafloor mining tools, picking up the about potato-sized nodules from the seafloor.[19][20][21]

By the time the International Seabed Authority was in place in 1994, interest in the extraction of nodules waned. Three factors were largely responsible:[citation needed]

  • Difficulty and expense of developing and operating mining technology that could economically remove the nodules from depths of five or six kilometers and transport them to the ocean surface
  • High taxes the international community would charge for the mining, and
  • Continuing availability of the key minerals from land-based sources at market prices.

At this time, the commercial extraction of polymetallic nodules was not considered likely to occur during the next two decades.[citation needed]

In recent times, nickel and other metal supply has needed to turn to higher cost deposits in order to meet increased demand, and commercial interest in nodules has revived. The International Seabed Authority has granted new exploration contracts and is progressing development of a Mining Code for The Area, with most interest being in the Clarion Clipperton Zone.[22]

Since 2011, a number of commercial companies have received exploration contracts. These include subsidiaries of larger companies like Lockheed Martin, DEME (Global Sea Mineral Resources, GSR), Keppel Corporation and China Minmetals, and smaller companies like Nauru Ocean Resources and Tonga Offshore Mining.[11]

The renewed interest in mining nodules has led to increased concern and scrutiny regarding possible environmental impacts.

Legal developments in 'The Area'

After the Second World War the United Nations started a lengthy process of developing international treaties that moved away from the then held concept of freedom of the seas.

By 1972, the promise of nodule exploitation was one of the main factors that led developing nations to propose that the deep seabed beyond the limits of national jurisdiction should be treated as a "common heritage of mankind", with proceeds to be shared between those who developed this resource and the rest of the international community. This initiative eventually resulted in the adoption (1982) of the United Nations Convention on the Law of the Sea (UNCLOS) and after negotiation of Part XI by 1994, the establishment of the International Seabed Authority, with responsibility for controlling all deep-sea mining in international areas. The first legislative achievement of this intergovernmental organization was the adoption (2000) of regulations for prospecting and exploration for polymetallic nodules, with special provisions to protect the marine environment from any adverse effects. The Authority followed this up (2001–2002) by signing 15-year contracts with seven private and public entities, giving them exclusive rights to explore for nodules in specified tracts of the seabed, each 75,000 square kilometers in size. The United States, whose companies were among the key actors in the earlier period of exploration, remains outside this compact as a non-party to the United Nations Convention on the Law of the Sea.[citation needed]

Per UNCLOS the Authority has four main functions. Essentially these are:

  • To administer the mineral resources of the seabed in the Area;
  • To enact rules, regulations and procedures relating to these resources;
  • To promote and encourage marine scientific research and development in the Area;
  • To protect and conserve the natural resources of the Area and prevent significant damage to the environment.

Currently the International Seabed Authority is defining and debating aspects of its Mining Code which encompasses polymetallic sulfides (seafloor massive sulfide deposits) and cobalt-rich crusts as well as polymetallic nodules. The Mining Code includes exploration and draft exploitation regulations, an environmental management plan for the Clarion Clipperton Zone, and recommendations for the guidance of contractors in terms of reporting, environmental impact assessment, expenditure reporting and training for scientists and engineers from developing nations.[23]

In addition to the Convention on Biological Diversity, on 19 June 2015 the General Assembly of the UN adapted resolution A/RES/69/292, "Development of an international legally-binding instrument under the United Nations Convention on the Law of the Sea on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction".[24] This resolution calls for a preparatory committee to be established to examine what this instrument could look like and what it would address specifically in addition to the existing environmental parts of UNCLOS. It would take into account the various reports of the co-chairs on the work of the relevant Ad Hoc Open-ended Informal Working Group. In due course an intergovernmental conference would review and debate the recommendations of the preparatory committee.

Environmental issues and sensitivities

Any future mining of nodules in The Area needs to be authorised by the International Seabed Authority and would need to quantify impact in advance via an environmental impact statement and associated environmental management plan. These assessments, monitoring plans and guidance controls would likely work at the scale of proposed operations.

The International Seabed Authority already has an environmental management plan that considers the entire Clarion Clipperton Zone and that includes reference areas that are not available for mining (termed Areas of Particular Environmental Interest).[25]

Environmental assessments would need to have an unbiased scientific basis, and to account for:

  • the remote nature of the nodules making detailed data collection challenging;
  • the large variety in scale (e.g. sub-decimeter nodule communities spread over thousands of kilometers) in terms of ecosystem function and biodiversity;
  • the severity and scale of local impacts (such as habitat destruction, resedimentation).

Past environmental studies such as the Deep Ocean Mining Environmental Study (DOMES) and resultant benthic impact experiments (BIE) concluded in part that trial mining at a reasonable scale would likely help best constrain real impacts from any commercial mining.[26]

Research shows that polymetallic nodule fields are hotspots of abundance and diversity for a highly vulnerable abyssal fauna.[27] Nodule mining could affect tens of thousands of square kilometers of these deep sea ecosystems. Nodule regrowth takes decades to millions of years and that would make such mining an unsustainable and nonrenewable practice. Any prediction about the effects of mining is extremely uncertain. Thus, nodule mining could cause habitat alteration, direct mortality of benthic creatures, or suspension of sediments, which can smother filter feeders.[28] Future environmental impact studies should address the impact on disruption and release of methane clathrate deposits in the deep oceans.[citation needed]

See also


  1. ^ Mero, John (1965). The mineral resources of the sea. Elsevier Oceanography Series.
  2. ^ a b c d International Seabed Authority (2010). A Geological Model of Polymetallic Nodule Deposits in the Clarion-Clipperton Fracture Zone and Prospector's Guide for Polymetallic Nodule Deposits in the Clarion Clipperton Fracture Zone. Technical Study: No. 6. ISBN 978-976-95268-2-2.
  3. ^ Hlawatsch, S.; Neumann, T.; van den Berg, C.M.G.; Kersten, M.; Hari, J.; Suess, E. (2002). "Fast-growing, shallow-water ferro-manganese nodules from the western Baltic Sea: origin and modes of trace element incorporation". Marine Geology. 182 (3–4): 373–387. Bibcode:2002MGeol.182..373H. doi:10.1016/s0025-3227(01)00244-4.
  4. ^ Callender, E.; Bowser, C. (1976). "Freshwater Ferromanganese Deposits". Au, U, Fe, Mn, Hg, Sb, W, and P Deposits. 7. Elsevier Scientific Publishing Community. pp. 341–394. ISBN 9780444599438.
  5. ^ Fike, D.A.; Grotzinger, J.P.; Pratt, L.M.; Summons, R.E. (2006). "Oxidation of the Ediacaran Ocea". Nature. 444 (7120): 744–747. Bibcode:2006Natur.444..744F. doi:10.1038/nature05345. PMID 17151665. S2CID 4337003.
  6. ^ Murray, J.; Renard, A.F. (1891). Report on Deep-Sea Deposits; Scientific Results Challenger Expedition.
  7. ^ Hein, James; Spinardi, Francesca; Okamoto, Nobuyuki; Mizell, Kira; Thorburn, Darryl; Tawake, Akuila (2015). "Critical metals in manganese nodules from the Cook Islands EEZ, abundances and distributions". Ore Geology Reviews. 68: 97–116. doi:10.1016/j.oregeorev.2014.12.011.
  8. ^ Von Stackelberg, U (1997). "Growth history of manganese nodules and crusts of the Peru Basin". Geological Society, London, Special Publications. 119 (1): 153–176. Bibcode:1997GSLSP.119..153V. doi:10.1144/GSL.SP.1997.119.01.11.
  9. ^ Mukhopadhyay, R.; Ghosh, A.K.; Iyer, S.D. (2007). The Indian Ocean Nodule Field Geology and Resource Potential: Handbook of Exploration and Environmental Geochemistry 10. Elsevier Science.
  10. ^ García, Marcelo; Correa, Jorge; Maksaev, Víctor; Townley, Brian (2020). "Potential mineral resources of the Chilean offshore: an overview". Andean Geology. 47 (1): 1–13. doi:10.5027/andgeoV47n1-3260.
  11. ^ a b c Lipton, Ian; Nimmo, Matthew; Parianos, John (2016). NI 43-101 Technical Report TOML Clarion Clipperton Zone Project, Pacific Ocean. AMC Consultants.
  12. ^ Kobayashi, Takayuki (October 2000). "Concentration profiles of 10Be in large manganese crusts". Nuclear Instruments and Methods in Physics Research Section B. 172 (1–4): 579–582. Bibcode:2000NIMPB.172..579K. doi:10.1016/S0168-583X(00)00206-8.
  13. ^ Blöthe, Marco; Wegorzewski, Anna; Müller, Cornelia; Simon, Frank; Kuhn, Thomas; Schippers, Axel (2015). "Manganese-Cycling Microbial Communities Inside Deep-Sea Manganese Nodules". Environ. Sci. Technol. 49 (13): 7692–7700. Bibcode:2015EnST...49.7692B. doi:10.1021/es504930v. PMID 26020127.
  14. ^ a b Novikov, C.V.; Murdmaa, I.O. (2007). "Ion exchange properties of oceanic ferromanganese nodules and enclosing pelagic sediments". Lithology and Mineral Resources. 42 (2): 137–167. doi:10.1134/S0024490207020034. S2CID 95097062.
  15. ^ Appelo, C.A.J.; Postma, D. (1999). "A consistent model for surface complexation on birnessite (δ−MnO2) and its application to a column experiment". Geochimica et Cosmochimica Acta. 63 (19–20): 3039–3048. doi:10.1016/S0016-7037(99)00231-8. ISSN 0016-7037.
  16. ^ Dzombak, David A.; Morel, François M. M. (1990). Surface Complexation Modeling: Hydrous Ferric Oxide. John Wiley & Sons. ISBN 978-0-471-63731-8.
  17. ^ Newton, Aric G.; Kwon, Kideok D. (2018). "Molecular simulations of hydrated phyllomanganates". Geochimica et Cosmochimica Acta. 235: 208–223. Bibcode:2018GeCoA.235..208N. doi:10.1016/j.gca.2018.05.021. ISSN 0016-7037.
  18. ^ Wegorzewski, A.V.; Kuhn, T. (2014). "The influence of suboxic diagenesis on the formation of manganese nodules in the Clarion Clipperton nodule belt of the Pacific Ocean". Marine Geology. 357: 123–138. Bibcode:2014MGeol.357..123W. doi:10.1016/j.margeo.2014.07.004.
  19. ^ Volkmann, Sebastian Ernst; Lehnen, Felix (21 April 2017). "Production key figures for planning the mining of manganese nodules". Marine Georesources & Geotechnology. 36 (3): 360–375. doi:10.1080/1064119X.2017.1319448. S2CID 59417262.
  20. ^ Volkmann, Sebastian Ernst; Kuhn, Thomas; Lehnen, Felix (2018-02-21). "A comprehensive approach for a techno-economic assessment of nodule mining in the deep sea". Mineral Economics. 31 (3): 319–336. doi:10.1007/s13563-018-0143-1. ISSN 2191-2203. S2CID 134526684.
  21. ^ Volkmann, Sebastian Ernst (2018). Blue mining - planning the mining of seafloor manganese nodules (Thesis). Aachen. doi:10.18154/rwth-2018-230772.
  22. ^ "Deep Seabed Mineral Resources".
  23. ^ "Mining Code".
  24. ^ United Nations. "Resolution adopted by the General Assembly on 19 June 2015: A/RES/69/292" (PDF).
  25. ^ "Biodiversity".
  26. ^ Ozturgut, E.; Trueblood, D. D.; Lawless, J. (1997). An overview of the United States's Benthic Impact Experiment. Proceedings of the International Symposium on Environmental Studies for Deep-Sea Mining. Metal Mining Agency of Japan.
  27. ^ University of Ghent press bulletin, June 7, 2016 Archived June 14, 2016, at the Wayback Machine
  28. ^ Glover, A. G.; Smith, C. R. (2003). "The deep-sea floor ecosystem: current status and prospects of anthropogenic change by the year 2025". Environmental Conservation. 30 (3): 21–241. doi:10.1017/S0376892903000225. S2CID 53666031.

Further reading

  • Abramowski, T.; Stoyanova, V. (2012). "Deep-Sea Polymetallic Nodules: Renewed Interest as Resources for Environmentally Sustainable Development". Proc 12th International Multidisciplinary Scientific GeoConference SGEM 2012. pp. 515–522.
  • Abramowski, T. (2016). Value chain of deep seabed mining, Book: Deep sea mining value chain: organization, technology and development, pp 9–18, Interoceanmetal Joint Organization
  • Cronan, D. S. (1980). Underwater Minerals. London: Academic Press. ISBN 978-0-12-197480-0.
  • Cronan, D. S. (2000). Handbook of Marine Mineral Deposits. Boca Raton: CRC Press. ISBN 978-0-8493-8429-5.
  • Cronan, D. S. (2001). "Manganese nodules". In Steele, J.; Turekian, K.; Thorpe, S. (eds.). Encyclopedia of Ocean Sciences. San Diego: Academic Press. pp. 1526–1533. ISBN 978-0-12-227430-5.
  • Earney, F. C. (1990). Marine Mineral Resources. London: Routledge. ISBN 978-0-415-02255-2.
  • Roy, S. (1981). Manganese Deposits. London: Academic Press. ISBN 978-0126010800.
  • Teleki, P. G.; Dobson, M. R.; Moore, J. R.; von Stackelberg, U. (1987). Marine Minerals: Advances in Research and Resource Assessment. Dordrecht: D. Riedel. ISBN 978-90-277-2436-6.

External links

  • Report on a World Almanac 1997 documentary Universe Beneath the Sea claiming evidence of rapid formation
  • The International Seabed Authority