From this week's Economist:
Race to the bottom: Mining the ocean floor is about to go mainstream
Despite the headline, this is still some years away. Selected quotes:
James Hein of the United States Geological Survey and colleagues estimated in a paper in 2012 that the CCZ
holds more nickel, cobalt and manganese than all known terrestrial deposits of those metals put together. The World Bank expects the battery industry’s demand for these, and other, minerals to increase if the transition to clean energy speeds up enough to keep global temperatures below the limits set in the Paris agreement on climate.
[...]
The idea of mining the CCZ is not new. The Pacific’s mineral nodules were discovered by HMS Challenger, a British research vessel that first dredged the abyssal depths in the 1870s. Lockheed Martin, an American defence contractor, tried prospecting the CCZ in the 1960s. Its caterpillar tracks were not reliable enough to operate at such depth, so the company imagined two Archimedes screws to drag its vehicle through the mud. (Lockheed’s deep-sea mining expertise was later used in a CIA operation to recover a Soviet submarine which sank in the CCZ in 1968.) At the time there was hyped speculation that deep-sea mining would develop rapidly by the 1980s. A lack of demand (and thus investment), technological capacity and appropriate regulation kept that from happening. The UN Convention on the Law of the Sea (UNCLOS), which set up the ISA, was not signed until 1982. (America has still not ratified it, and thus cannot apply to the ISA for sea-floor-mining permits.)
[...]
If P2 succeeds, it will be time for P3, which will be the size of a small house. It will have two drone escorts, one to move ahead of it and one behind. They will monitor how much silt it disturbs, and will shut down the operation if necessary. Thus, P3 will be able to steer along the seabed autonomously. DEME will then build a customised surface vessel, ending up in about 2025 with a new kind of mining operation, at a total cost of $600 million.