Deep sea mining

Deep sea mining is the extraction of minerals from the ocean floor found at depths of to . As of 2021, the majority of marine mining efforts were limited to shallow coastal waters, where sand, tin and diamonds are more readily accessible. It is a growing subfield of experimental seabed mining. Three types of deep sea mining have generated interest: polymetallic nodule mining, polymetallic sulfide mining, and cobalt-rich ferromanganese crusts. The majority of proposed deep sea mining sites are near polymetallic nodules or active and extinct hydrothermal vents at depth. The vents create globular or "massive" sulfide deposits that contain valuable metals such as silver, gold, copper, manganese, cobalt, and zinc. The deposits are mined using hydraulic pumps or bucket systems that carry ore to the surface for processing.
Marine minerals include sea-dredged and seabed minerals. Sea-dredged minerals are normally extracted by dredging operations within coastal zones, at depths of about 200 m. Minerals normally extracted from these depths include sand, silt and mud for construction purposes, mineral rich sands such as ilmenite and diamonds.
The environmental impact of deep sea mining is disputed. Environmental advocacy groups such as Greenpeace and the Deep Sea Mining Campaign have argued against seabed mining because of the potential for damage to deep sea ecosystems and pollution by heavy metal-laden plumes. Environmental activists and state leaders have called for moratoriums or permanent bans. Anti-seabed mining campaigns have won the support of industry, including some increasingly reliant on the metals such mining can provide. Individual countries with significant deposits of seabed minerals within their large exclusive economic zones (EEZ's) are making their own decisions pertaining to deep sea mining, exploring how to minimize environmental damage, or deciding not to proceed. Some companies are attempting to build deep sea mining equipment that preservers marine habitats.
As of 2022 no commercial deep sea mining was underway. However, the International Seabed Authority granted 19 exploration licenses for polymetallic nodules within the Clarion Clipperton Zone. In 2022 the Cook Islands Seabed Minerals Authority (SBMA) granted 3 exploration licenses for polymetallic nodules within their EEZ.
At some point, mining could proceed at a range of scales within the oceans. Related technologies could involve robotic mining machines, as well as surface ships, and onshore metal refineries.
Wind farms, solar energy, electric cars, and improved battery technologies use a high volume and wide range of metals including ‘green’ or ‘critical’ metals, many of which are in relatively short supply. Seabed mining could provide many of these metals.
Sites
Ocean mining sites focus on large areas of polymetallic nodules or active and extinct hydrothermal vents at about 3,000 – 6,500 meters deep. The vents create sulfide deposits, which collect metals such as silver, gold, copper, manganese, cobalt, and zinc. The deposits are mined using hydraulic pumps or bucket systems.
An additional site that is being explored and looked at as a potential deep sea mining site is the Clarion-Clipperton Fracture Zone (CCZ). The CCZ stretches over 4.5 million square kilometers of the Northern Pacific Ocean between Hawaii and Mexico. Scattered across the abyssal plain are trillions of polymetallic nodules, potato-sized rocklike deposits containing minerals such as magnesium, nickel, copper, zinc, cobalt, and others.
Polymetallic nodules are also abundant in the Central Indian Ocean Basin and the Peru Basin.
Papua New Guinea was the first country to approve a DSM permit, to Solwara 1. This was despite three independent reviews of the environmental impact statement mine alleged significant gaps and flaws in the underlying science.
Minerals
Seabed minerals are mostly located at depths of 1-6 km comprise three main types:
Polymetallic or manganese nodules are found at depths of 4-6 km, largely on abyssal plains. Manganese and related hydroxides precipitate from ocean water or sediment-pore water around a nucleus, which may be a shark’s tooth or a quartz grain, forming potato-shaped nodules some 4–14 cm in diameter. They accrete at rates of 1–15 mm per million years. These nodules are rich in elements including rare earths, cobalt, nickel, copper, molybdenum, lithium, and yttrium. The largest deposits occur in the Pacific Ocean between Mexico and Hawaii in the Clarion Clipperton Fracture Zone. The Cook Islands contains the world’s fourth largest deposit in the South Penrhyn basin close to the Manihiki Plateau.
Polymetallic or seabed sulfide deposits form in active oceanic tectonic settings such as island arcs and back-arcs and mid ocean ridge environments. These deposits are associated with hydrothermal activity and hydrothermal vents at sea depths mostly between 1 and 4 km. These minerals are rich in copper, gold, lead, silver and others. They are found within the Mid Atlantic Ridge system, around Papua New Guinea, Solomon Islands, Vanuatu, and Tonga and other similar ocean environments.
Cobalt-rich crusts (CRC’s) form on sediment-free rock surfaces around oceanic seamounts, ocean plateaus, and other elevated features. The deposits are found at depths of 600–7000 m and form ‘carpets’ of polymetallic rich layers about 30 cm thick at the feature surface. Crusts are rich in a range of metals including cobalt, tellurium, nickel, copper, platinum, zirconium, tungsten, and rare earth elements. They are found on seamounts in the Atlantic and Indian Oceans, as well as countries such as the Pacific Federated States of Micronesia, Marshall Islands, and Kiribati.
Diamonds are mined from the seabed by De Beers and others.
Cobalt-rich ferromanganese formations are found at various depths between 400 and 7000 meters. These formations are a type of Manganese crust deposit. The substrates consist of layered iron and magnesium (Fe-Mn oxyhydroxide deposits ) that host mineralization.
Cobalt-rich ferromanganese formations exist in two categories depending on the depositional environment:
hydrogenetic cobalt-rich ferromanganese crusts
hydrothermal crusts and encrustations.
Temperature, depth and seawater sources are dependent variables that shape how the formations grow. Hydrothermal crusts precipitate quickly, near 1600–1800 mm/Ma and grow in hydrothermal fluids at approximately 200 °C. Hydrogenetic crusts grow much slower at 1–5 mm/Ma, but offer higher concentrations of critical metals.
Submarine seamount provinces, linked to hotspots and seafloor spreading, vary in depth along the ocean floor. These seamounts show characteristic distributions that connect them to cobalt-rich ferromanganese formation. In the Western Pacific, a study conducted at <1500 m to 3500 mbsl reported that cobalt crusts are concentrated in seamount sections on less than 20° slopes. The high-grade cobalt crust in the Western Pacific trended /correlated with latitude and longitude, a region within 150°E‐140°W and 30°S‐30°N
Polymetallic sulphides are available for extraction from seafloor massive sulfide deposits, composed on and within the seafloor base when mineralized water discharges from a hydrothermal vent. The hot, mineral-rich water precipitates and condenses when it meets cold seawater. The stock area of the chimney structures of hydrothermal vents can be highly mineralized.
Polymetallic nodules/manganese nodules are found on abyssal plains, in a range of sizes, some as large as 15 cm long. Nodules are recorded to have average growth rates near 10–20 mm/Ma.
The Clipperton Fracture Zone hosts the largest untapped deposit nickel resource; polymetallic or manganese nodules sit on the seafloor. These nodules require no drilling or excavation. Nickel, cobalt, copper and manganese make up nearly 100% of the nodules.
Projects
The world's first large-scale mining of hydrothermal vent mineral deposits was carried out by Japan Oil, Gas and Metals National Corporation (JOGMEC) from August - September, 2017, using the research vessel Hakurei, at the 'Izena hole/cauldron' vent field within the hydrothermally active back-arc Okinawa Trough, which contains 15 confirmed vent fields according to the InterRidge Vents Database.
A deep sea mining venture in Papua New Guinea, the Solwara 1 Project, was granted a mining permit to begin mining a high grade copper-gold resource from a weakly active hydrothermal vent. This project generated backlash from community and environmental activists The Deep Sea Mining Campaign and Alliance of Solwara Warriors, comprising 20 communities in the Bismarck and Solomon Seas are seeking to ban seabed mining in Papua New Guinea and across the Pacific. They primarily argue that DSM decision-making has not adequately addressed Free Prior and Informed Consent for affected communities and have not adhered to the precautionary principle. The project operated at 1600 mbsl in the Bismarck Sea, New Ireland Province. Using remotely operated underwater vehicles (ROV) technology developed by UK-based Soil Machine Dynamics, Nautilus Minerals Inc. announced plans to begin full-scale mining. However a dispute with Papua-New Guinea delayed production and operation until early 2018. In September 2019, the project ended as Nautlilus went into administration.
In the 1970s Shell, Rio Tinto (Kennecott) and Sumitomo conducted pilot test work, recovering over ten thousand tons of nodules in the CCZ. Mining claims registered with the International Seabed Authority (ISA) are mostly located in the CCZ, most commonly in the manganese nodule province. As of 2019 the ISA had entered into 18 contracts with private companies and national governments in the CCZ.
In 2019, the government of the Cook Islands passed two deep sea mining laws. The Sea Bed Minerals (SBM) Act of 2019 "enable the effective and responsible management of the seabed minerals of the Cook Islands in a way that also...seeks to maximize the benefits of seabed minerals for present and future generations of Cook Islanders." Sea Bed Minerals (Exploration) Regulations Act and the Sea Bed Minerals Amendment Act were passed by Parliament in 2020 and 2021, respectively. As much as 12 billion tons of polymetallic nodules occupy the ocean floor in the Cook Islands EEZ.
On November 10, 2020, the Chinese submersible Fendouzhe (Striver) reached the bottom of the Mariana Trench 10,909 meters (35,790 feet). Chief designer Ye Cong said the seabed was abundant with resources and a "treasure map" can be made.
Promising sulfide deposits (an average of 26 parts per million) were found in the Central and Eastern Manus Basin around PNG and the crater of Conical Seamount to the east. It offers relatively shallow water depth of 1050 m, along with the close proximity of a gold processing plant.
In 2023 a Canadian company, The Mining Company, partnered with a Micronesian island to start mining.
Extraction methods
Robotics and AI technologies are under development.
Remotely operated vehicles (ROVs) are used to collect mineral samples from prospective sites. Using drills and other cutting tools, the ROVs obtain samples. A mining ship or station is set up to mine the area.
The continuous-line bucket system (CLB) is the older approach. It operates like a conveyor-belt, running from the bottom to the surface where a ship or mining platform extracts the minerals, and returns the tailings to the ocean. Hydraulic suction mining instead lowers a pipe to the seafloor and pumps nodules up to the ship. Another pipe returns the tailings to the mining site.
Process
During prospecting, exploration and resource assessment phases, value is added to intangible assets. In the intermediate phase – the pilot mining test – enables “resources” to attain the “reserves” classification.
The exploration phase involves operations such as bottom scanning and sampling using technologies such as echo-sounders, side scan sonars, deep-towed photography, ROVs, and autonomous underwater vehicles (AUV).
Mining involves gathering material, vertical transport, storing, offloading, transport, and metallurgical processing.
Polymetallic minerals require special treatment. Issues include spatial tailing discharges, sediment plumes, disturbance to the benthic environment, and analysis of regions affected by seafloor machines.
Environmental impacts
Deep sea mining (like all mining) must consider potential its environmental impacts. Deep sea mining has yet to receive a comprehensive evaluation of such impacts.
Environmental impacts include sediment plumes, disturbance of the bottom, tailing disposition,
Technology is under development to mitigate these issues. This includes selective pick-up technology that does not pick up nodules that contain life and leaves behind some nodules to maintain the habitat.
However, some experts claim that mining will disturb the benthic layer, increase toxicity of the water column, and produce sediment plumes. Removing parts of the sea floor disturbs the habitat of benthic organisms. Aside from mining's direct impact, leakage, spills, and corrosion could alter the habitat.
Sediment plumes have attracted the most attention. Plumes are caused when mine tailings (usually fine particles) are returned to the ocean, leaving a floating cloud of particles. The two types of plumes are near-bottom plumes and surface plumes. Near-bottom plumes occur when tailings are returned to the bottom. Particles increase the turbidity, or cloudiness, of the water, clogging filter-feeding organisms. Surface plumes can spread over vast areas, inhibiting growth of photosynthesizing organisms, including coral and phytoplankton.
Opponents point to the grave and irreversible damage mining could cause to fragile deep sea ecosystems. Fauna and Flora International and World Wide Fund for Nature, broadcaster David Attenborough, and companies such as BMW, Google, Volvo Cars, and Samsung called for a moratorium.
Marine life
Polymetallic nodule fields are hotspots of abundance and diversity for highly vulnerable abyssal fauna. Because deep sea mining is a relatively new field, the full consequences of mining this ecosystem are unknown.
Concerns about impacts on marine life include:
- removal of parts of the sea floor disrupt the benthic layer. Preliminary studies indicated that the seabed requires decades to recover from minor disturbances.
- increased toxicity of the water column
- sediment plumes from tailings.
- leakage, spills, and corrosion inject potentially toxic materials into the water column
Nodule fields provide hard substrate on the pelagic red clay bottom, attracting macrofauna. A baseline study of benthic communities in the CCZ assessed a 350 square mile area with an ROV. They reported that the area contained one of the most diverse abyssal plain megafaunal communities. The megafauna (species longer than ) included glass sponges, anemones, eyeless fish, sea stars, psychropotes, amphipods, and isopods. Macrofauna (species longer than 0.5mm) were reported to have high local species diversity, numbering 80 -100 per square meter. The highest species diversity was found among polymetallic nodules. In a follow-up survey, researchers identified over 1,000 species, 90% previously unknown, with over 50% dependent on polymetallic nodules for survival; all were identified in areas with potential for seabed mining.
However, biomass loss stemming from deep sea mining was estimated to be significantly smaller than that from land ore mining. It is estimated that land ore mining will lead to a loss of 568 megatons of biomass (approximately the same as that of the entire human population) versus 42 megatons of biomass from DSM. In addition, land ore mining will lead to a loss of 47 trillion megafauna organisms, whereas deep-sea mining is expected to lead to a loss of 3 trillion megafauna organisms. Another report reported that deep sea mining is approximately 25 times worse for biodiversity than land mining.
Sediment plumes
Sediment plumes are caused when the tailings from mining (usually fine particles) are discharged into the ocean, creating a cloud of particles. Plumes are discharged either at the bottom or at the surface.
Near-bottom plumes occur when the tailings are pumped back down to the mining site. The particles increase the turbidity, or cloudiness, of the water, clogging filter-feeding apparatus used by benthic organisms.
Surface plumes cause a more serious problem. Depending particle size and water currents, surface plumes could spread widely. Sunlight penetrates less deeply, impacts photosynthesizers such as zooplankton, in turn affecting the food web. Sediment can be resuspend following storms, causing further damage. Metals carried by the plumes can accumulate in tissues of shellfish. This bioaccumulation works its way through the food web, impacting predators, including humans.
Noise and light pollution
Deep sea mining generates ambient noise in normally-quiet pelagic environments. Anthropogenic noise affects deep sea fish species and marine mammals. Impacts include behavior changes, communication difficulties, and temporary and permanent hearing damage.
DSM sites are normally pitch dark. Mining efforts may drastically increase light levels. Shrimp found at hydrothermal vents suffered permanent retinal damage when exposed to floodlights from submersibles. Behavioral changes include vertical migration patterns, ability to communicate, and ability to detect prey.
Laws and regulations
The international law on deep sea mining is contained in the United Nations Conventions on the Law of the Sea (UNCLOS). The convention set up the International Seabed Authority (ISA), which regulates DSM outside a given nations’ Exclusive Economic Zone (a area surrounding coastal nations). The ISA requires nations interested in mining to explore two equivalent mining sites and turn one over to the ISA, along with a transfer of mining technology over a 10- to 20-year period. This seemed reasonable at the time because it was widely believed that nodule mining would be extremely profitable. However, these strict requirements led some industrialized countries to refuse to sign the treaty.
DSM within national EEZ's seabed mining is governed by national laws. New Zealand is one of the few countries that have established a legal and institutional DSM framework.
A DSM moratorium was adopted at the Global biodiversity summit in 2021. At the 2023 ISA meeting a DSM moratorium was enacted.
The United States did not ratify UNCLOS. Instead, it is governed by the Deep Seabed Hard Mineral Resources Act, which was originally enacted in 1980.
New Zealand's Foreshore and Seabed Act was enacted in 2004 and then repealed following Māori objections, who protested the Act as a "sea grab". The Act was replaced with the 2011 Marine and Coastal Area Bill.
History
In the 1960s, the prospect of deep-sea mining was assessed in J. L. Mero's Mineral Resources of the Sea. Nations including France, Germany and the United States dispatched research vessels in search of deposits. Initial estimates of DSM viability were exaggerated. Depressed metal prices led to the near abandonment of nodule mining by 1982. From the 1960s to 1984 an estimated US $650 million was spent on the venture, with little to no return.
A 2018 article argued that "the 'new global gold rush' of deep sea mining shares many features with past resource scrambles – including a general disregard for environmental and social impacts, and the marginalisation of indigenous peoples and their rights".
2020s
See also
, the process of creating holes for oil mining in deep sea.
, concretions of manganese and other minerals formed over thousands of years on the abyssal plains; sought after for deep sea mining projects.
, location of interest for deep sea mining
Deepsea mining in Namibia
References
External links
The Deep Sea Mining Summit 2023 "The international forum for deep sea mining professionals"
"Who Will Claim Common Heritage?–Corporate interests endanger international agreement on deep seabed minerals" in Multinational Monitor
Deep Sea Mining – 8 min video on Australian science TV, June 2011
Geophysical Methods for the Mapping of Deep-Sea Mineral Deposits – November 2014 Ocean News & Technology magazine
"Why are countries laying claim to the deep-sea floor?" - BBC article 21 June 2017
Assessment of the Different technologies for Vertical Hydraulic Transport in Deep Seam Mining Applications
Mining the Deep Sea
Underwater mining
Mining
Oceans