The United States and Japan are discussing cooperation around rare-earth-bearing mud located near Minamitorishima, Japan’s easternmost island. The deposits lie at a depth of roughly 6 kilometres within Japan’s exclusive economic zone.
The project is often described as a plan for the world’s deepest underwater mine. That wording is technically misleading. The proposed system would not use conventional tunnels or underwater workers. A vessel would lower equipment to the seabed, loosen the mud and pump it through a long pipe to the surface, where it would be dewatered and transported for processing.
Japan has already demonstrated the basic extraction technology. In January and February 2026, the research vessel Chikyu recovered approximately 50 tonnes of mud from 5,569 metres.
The resource estimate is more than 16 million tonnes of rare-earth oxides. The composition may be even more important than the volume: around 54% of the tested rare-earth content consisted of medium and heavy elements. The samples included yttrium, gadolinium and dysprosium, which are valuable for high-performance magnets, electronics, robotics, electric motors, aerospace systems and defense technologies.
The estimate that yttrium could equal 780 years of current global demand must be treated cautiously. It is a theoretical comparison with present consumption, not a guarantee that 780 years of commercially usable supply can be produced.
China’s dominance explains the interest of Washington and Tokyo. In 2024, China accounted for around 60% of global mined magnet rare earths, 91% of refined output and 94% of sintered permanent-magnet production.
This is why a new seabed deposit does not automatically create supply-chain independence. A genuine alternative requires:
• extraction;
• dewatering;
• separation;
• purification;
• metal production;
• permanent magnets.
Japan plans a larger test for February 2027, lasting approximately one month and targeting up to 350 tonnes of mud per day. The results are expected to support an assessment of domestic production by March 2028.
Environmental risk is also unresolved. Low levels of radioactive and toxic material in tested samples may simplify processing, but they do not eliminate the risks of sediment plumes, seabed damage, noise, vibration and long-term disruption of deep-ocean ecosystems.
The Burke Index reveals the strategic asymmetry behind the project. The United States scores 95.4/100 in technological sovereignty and 650.9/700 overall. Japan scores 90/100 in technological sovereignty and 592.2/700 overall. Japan’s technological strength is accompanied by military sovereignty of 71.9, dependence on the U.S. security partnership, imported energy and food, demographic pressure and public debt of 216–234% of GDP.
The project therefore has two dimensions.
For Japan, it is an attempt to convert domestic engineering, robotics and maritime capability into greater resource autonomy.
For the United States, it is an opportunity to help construct an alternative critical-minerals network with military and industrial applications.
The deeper conclusion is that technological sovereignty is not the same as control over a single technology. Japan may prove that it can lift rare-earth mud from the deep ocean, but strategic independence requires control of the entire chain from seabed to magnet.
If the project produces only raw material while China retains separation, refining and magnet manufacturing, the dependence will be reduced only at the surface level.
The six-kilometre test is therefore a test of more than deep-sea engineering. It is a test of whether an alliance can turn a resource discovery into a complete sovereign capability.
Find the United States and Japan in the full Burke ranking: https://ibi.institute/index/2025
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