Polymetallic nodules, also called manganese nodules, are rock 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 having economic interest.
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 (mammilated or knobby) texture and vary from spherical in shape to typically oblate, sometimes prolate, or are otherwise irregular. The bottom surface, buried in sediment, is generally rougher than the top due to a different type of growth.
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. 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.
Polymetallic nodules are found in both shallow (e.g. the Baltic Sea) and deeper waters (e.g. the central Pacific), even in lakes, 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.
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.
Their composition varies by location, and sizeable deposits have been found in four 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.
All of these deposits are in international waters apart from the Penrhyn Basin, which lies within the exclusive economic zone of the Cook Islands.
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. 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. Several processes are hypothesized to be involved in the formation of nodules, including the precipitation of metals from seawater (hydrogenous), 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). Several of these processes may operate concurrently or they may follow one another during the formation of a nodule.
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. 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 CCZ nodules 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.
The chemical composition of nodules varies according to the kind of manganese minerals and the size and characteristics of the core. Those of greatest economic interest contain manganese (27-30%), nickel (1.25-1.5 %), copper (1-1.4 %) and cobalt (0.2-0.25 %). Other constituents include iron (6%), silicon (5%) and aluminium (3%), 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.
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, the Federal Republic of 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-seventies, two of the international joint ventures succeeded in collecting several hundred ton quantities of manganese nodules from the abyssal plains (18,000 feet, 5.5 km + depth) of the eastern equatorial Pacific Ocean. 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 whilst simultaneously performing a sub-bottom profile with a derived, vertically oriented, low-frequency acoustic beam.
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.
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.
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 vehicle (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.
By the time the International Seabed Authority was in place in 1994, interest in the extraction of nodules waned. Three factors were largely responsible:
At this time, the commercial extraction of polymetallic nodules was not considered likely to occur during the next two decades.
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.
Since 2011, a number of commercial companies have received exploration contracts. These include subsidiaries of larger companies like Lockheed Martin, DEME, Keppel Corporation and China Minmetals and smaller companies like Nauru Ocean Resources Inc and Tonga Offshore Mining Limited.
The renewed interest in mining nodules has led to increased concern and scrutiny regarding possible environmental impacts.
Within the value chain concept of manganese nodules mining, seven main stages from prospecting to sales can be identified:
|1. Prospecting and application
3. Resource assessment, evaluation and mine planning
|Value is added in relation to resource classification|
(3-4) – Pilot mining test – Intermediate phase – a phase where the value of the project actually starts. For mature terrestrial mining the value can start as early as prospecting and application.
|4. Extraction, lifting and surface operations
5. Offshore and onshore logistics, transport operations
6. Metallurgical processing stage
7. Distribution and sales
|Value is added basing on product processing|
The exact components and stages can be arranged individually for the particular deep-sea mining projects of various contractors. The current focus of deep sea mining projects is aimed at exploration where phases of mining, extraction, lifting and surface operation techniques are now in planning or are tested on a smaller scale.
As presented in the list the main steps of manganese nodules project value chain can be differentiated using the criteria of the type of activities where the value is actually added. Whereas within prospecting, exploration and resource assessment phases the value is added to intangible assets, for the extraction, processing and distribution phases the value increases with relation to product processing. There is an intermediate phase – the pilot mining test which could be considered to be an inevitable step in the shift from “resources” to “reserves” classification, where the actual value starts.
Exploration phase involves such operations as locating, sea bottom scanning and sampling using technologies such as echo-sounders, side scan sonars, deep-towed photography, ROVs, AUVs. The resource valuation incorporates the examination of data in the context of potential mining feasibility. A reliable mineral resources classification is a necessary condition for economic feasibility assessment. At first a sample of nodules is taken and it is processed in ship laboratories according to the specified technology in order to determine such quantities as nodules abundance and chemical content of the deposit. The spatial distribution of nodule ore abundance and metal content is processed in GIS computer systems. Eventually statistical analysis provides for the estimation of nodule tonnage and metals in the deposit, which are the subject of the report on mineral resources classification.
Value chain based on product processing involves such operations as actual mining (or extraction), vertical transport, storing, offloading, transport, metallurgical processing for final products. Unlike the exploration phase, the value increases after each operation on processed material eventually delivered to the metal market. This phase is also the subject of a taxation procedure. Logistics involves technologies analogous to those applied in land mines. This is also the case for the metallurgical processing, although rich and polymetallic mineral composition which distinguishes marine minerals from its land analogs requires special treatment of the deposit. Environmental monitoring and impact assessment analysis relate to the temporal and spatial discharges of the mining system if they occur, sediment plumes, disturbance to the benthic environment and the analysis of the regions affected by seafloor machines. This involves an examination of disturbances near the seafloor, as well as disturbances near the surface. Observations include baseline comparisons for the sake of quantitative impact assessments. After a certain reporting period feedback information is provided to improve the sustainability of the mining process.
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 Law of the Sea Convention.
Per UNCLOS the Authority has four main functions. Essentially these are:
Currently the International Seabed Authority is defining and debating aspects of its Mining Code which encompasses Polymetallic Sulphides (Seafloor massive sulphide 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.
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. This resolution calls for a PrepCom 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 PrepCom.
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).
Environmental assessments would need to have an unbiased scientific basis, and to account for:
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.
Research shows that polymetallic nodule fields are hotspots of abundance and diversity for a highly vulnerable abyssal fauna. 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 sediment, which can smother filter feeders. Future environmental impact studies should address the impact on disruption and release of methane clathrate deposits in the deep oceans.
Crystal growth, is the process where a pre-existing crystal becomes larger as more molecules or ions add in their positions in the crystal lattice or a solution is developed into a crystal and further growth is processed. A crystal is defined as being atoms, molecules, or ions arranged in an orderly repeating pattern, a crystal lattice, extending in all three spatial dimensions. So crystal growth differs from growth of a liquid droplet in that during growth the molecules or ions must fall into the correct lattice positions in order for a well-ordered crystal to grow. The schematic shows a very simple example of a crystal with a simple cubic lattice growing by the addition of one additional molecule.
When the molecules or ions fall into the positions different from those in a perfect crystal lattice, crystal defects are formed. Typically, the molecules or ions in a crystal lattice are trapped in the sense that they cannot move from their positions, and so crystal growth is often irreversible, as once the molecules or ions have fallen into place in the growing lattice, they are fixed in place.Groutite
Groutite is a manganese oxide mineral with formula Mn3+O(OH). It is a member of the diaspore group and is trimorphous with manganite and feitknechtite. It forms lustrous black crystals in the orthorhombic system.
It occurs in weathered banded iron formations, metamorphosed manganese ore bodies and hydrothermal ore environments.
It was first described in 1945 for an occurrence in the Mahnomen mine, Cuyuna Range, Crow Wing County, Minnesota and named for petrologist Frank Fitch Grout (1880–1958), of the University of Minnesota.Günther Friedrich
Günther Friedrich (15 April 1929 – 24 November 2014) was a German mineralogist and university professor at the RWTH University at Aachen. He was an expert in the field of the creation of marine Manganese nodule concretions.Moebjergarctus manganis
Moebjergarctus manganis is a species of tardigrades. It is the only species in the genus Moebjergarctus, part of the family Halechiniscidae. The species has been found in the southeastern part of the Pacific Ocean. They were first named and described by Christian Bussau in 1992.Natural resource economics
Natural resource economics deals with the supply, demand, and allocation of the Earth's natural resources. One main objective of natural resource economics is to better understand the role of natural resources in the economy in order to develop more sustainable methods of managing those resources to ensure their availability to future generations. Resource economists study interactions between economic and natural systems, with the goal of developing a sustainable and efficient economy.Nii Allotey Odunton
Nii Allotey Odunton, a mining engineer from Ghana, is Secretary-General of the International Seabed Authority, serving a four-year term from January 1, 2009.Seabed
The seabed (also known as the seafloor, sea floor, or ocean floor) is the bottom of the ocean.Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean or the Austral Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. As such, it is regarded as the fourth largest of the five principal oceanic divisions: smaller than the Pacific, Atlantic, and Indian Oceans but larger than the Arctic Ocean. This oceanic zone is where cold, northward flowing waters from the Antarctic mix with warmer subantarctic waters.
By way of his voyages in the 1770s, James Cook proved that waters encompassed the southern latitudes of the globe. Since then, geographers have disagreed on the Southern Ocean's northern boundary or even existence, considering the waters as various parts of the Pacific, Atlantic, and Indian Oceans, instead. However, according to Commodore John Leech of the International Hydrographic Organization (IHO), recent oceanographic research has discovered the importance of Southern Circulation, and the term Southern Ocean has been used to define the body of water which lies south of the northern limit of that circulation. This remains the current official policy of the IHO, since a 2000 revision of its definitions including the Southern Ocean as the waters south of the 60th parallel has not yet been adopted. Others regard the seasonally-fluctuating Antarctic Convergence as the natural boundary.The maximum depth of the Southern Ocean, using the definition that it lies south of 60th parallel, was surveyed by the Five Deeps Expedition in early February 2019. The expedition's multibeam sonar team identified the deepest point at 60° 28' 46"S, 025° 32' 32"W, with a depth of 7,434 meters. The expedition leader and chief submersible pilot Victor Vescovo, has proposed naming this deepest point in the Southern Ocean the "Factorian Deep," based on the name of the manned submersible DSV Limiting Factor, in which he successfully visited the bottom for the first time on February 3, 2019.Soviet submarine K-129 (1960)
The K-129 was a Project 629A (NATO reporting name Golf II) diesel-electric powered submarine that served in the Soviet Navy's Pacific Fleet– one of six Project 629 strategic ballistic missile submarines attached to the 15th Submarine Squadron based at Rybachiy Naval Base, Kamchatka, commanded by Rear Admiral Rudolf A. Golosov.
In January 1968, the 15th Submarine Squadron was part of the 29th Ballistic Missile Division at Rybachiy, commanded by Admiral Viktor A. Dygalo. K-129's commander was Captain First Rank V.I. Kobzar. K-129 carried hull number 722 on her final deployment during which she sank on 8 March 1968. It was one of four mysterious submarine disappearances in 1968, the others being the Israeli submarine INS Dakar, the French submarine Minerve and the U.S. submarine USS Scorpion. The Soviet Navy deployed a huge flotilla of ships to search for her but never found her wreck. The wreck was located by the US Navy in August 1968.
The United States attempted to recover the boat in 1974 in a secret Cold War-era effort named Project Azorian. The vessel's position 4.9 kilometres (16,000 ft) below the surface was the greatest depth from which an attempt had been made to raise a ship—only a part of the submarine was recovered despite efforts. The cover story used was that the salvage vessel was engaged in commercial manganese nodule mining.Todorokite
Todorokite is a rare complex hydrous manganese oxide mineral with the formula (Na,Ca,K,Ba,Sr)1-x(Mn,Mg,Al)6O12·3-4H2O. It was named in 1934 for the type locality, the Todoroki mine, Hokkaido, Japan. It belongs to the prismatic class 2/m of the monoclinic crystal system, but the angle β between the a and c axes is close to 90°, making it seem orthorhombic. It is a brown to black mineral which occurs in massive or tuberose forms. It is quite soft with a Mohs hardness of 1.5, and a specific gravity of 3.49 - 3.82. It is a component of deep ocean basin manganese nodules.