Polymetallic nodules in the context of "Nodule (geology)"

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⭐ Core Definition: Polymetallic nodules

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. Depending on their composition and authorial choice, they may also be called ferromanganese nodules. Ferromanganese nodules are mineral concretions composed of silicates and insoluble iron and manganese oxides that form on the ocean seafloor and terrestrial soils. The formation mechanism involves a series of redox oscillations driven by both abiotic and biotic processes. As a byproduct of pedogenesis, the specific composition of a ferromanganese nodule depends on the composition of the surrounding soil. The formation mechanisms and composition of the nodules allow for couplings with biogeochemical cycles beyond iron and manganese. The high relative abundance of nickel, copper, manganese, and other rare metals in nodules has increased interest in their use as a mining resource.

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. 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, 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.

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Polymetallic nodules in the context of Deep sea mining

Deep sea mining is the extraction of minerals from the seabed of the deep sea. The main ores of commercial interest are polymetallic nodules, which are found at depths of 4–6 km (2.5–3.7 mi) primarily on the abyssal plain. The Clarion–Clipperton zone (CCZ) alone contains over 21 billion metric tons of these nodules, with minerals such as copper, nickel, cobalt and manganese making up roughly 30% of their weight. It is estimated that the global ocean floor holds more than 120 million tons of cobalt, five times the amount found in terrestrial reserves.

As of July 2024, only exploratory licenses have been issued, with no commercial-scale deep sea mining operations yet. The International Seabed Authority (ISA) regulates all mineral-related activities in international waters and has granted 31 exploration licenses so far: 19 for polymetallic nodules, mostly in the CCZ; 7 for polymetallic sulphides in mid-ocean ridges; and 5 for cobalt-rich crusts in the Western Pacific Ocean. There is a push for deep sea mining to commence by 2025, when regulations by the ISA are expected to be completed.

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Polymetallic nodules in the context of International Seabed Authority

The International Seabed Authority (ISA; French: Autorité internationale des fonds marins) is a Kingston, Jamaica-based intergovernmental body of 167 member states and the European Union. It was established under the 1982 UN Convention on the Law of the Sea (UNCLOS) and its 1994 Agreement on Implementation. The ISA's dual mission is to authorize and control the development of mineral related operations in the international seabed, which is considered the "common heritage of all mankind", and to protect the ecosystem of the seabed, ocean floor and subsoil in "The Area" beyond national jurisdiction. The ISA is responsible for safeguarding the international deep sea, defined as waters below 200 meters (656 feet), where photosynthesis is hampered by inadequate light. Governing approximately half of the total area of the world's oceans, the ISA oversees activities that might threaten biological diversity and harm the marine environment.

Since its inception in 1994, the ISA has approved over two dozen ocean floor mining exploration contracts in the Atlantic, Pacific and Indian Oceans. The majority of these contracts are for exploration in the Clarion–Clipperton zone between Hawaii and Mexico, where polymetallic nodules contain copper, cobalt and other minerals essential for powering electric batteries. To date, the Authority has not authorized any commercial mining contracts as it continues to deliberate over regulations amid global calls for a moratorium on deep sea mining. Scientists and environmentalists warn that such mining could wreak havoc on the ocean, a crucial carbon sink and home to rare and diverse species.

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