"We have found deposits that are just two to four metres from the seabed surface at higher concentrations than anybody ever thought existed, and it won't cost much at all to extract," said professor Yasuhiro Kato from Tokyo University, the leader of the team.
While America, Australia, and other countries have begun to crank up production of the seventeen rare earth elements, they have yet to find viable amounts of the heavier metals such as dysprosium, terbium, europium, and ytterbium that are most important.
China has a near total monopoly in the heavier end of the spectrum, though it is also the dominant supplier of the whole rare earth complex after driving rivals out of business in the 1990s. It still accounts for 97pc of global supply.
Beijing shocked the world when it suddenly began to restrict exports in 2009, prompting furious protests and legal complaints by both the US and the EU at the World Trade Organisation. China claimed that it was clamping down on smuggling and environmental abuse.
"Their real intention is to force foreign companies to locate plant in China. They're saying `if you want our rare earth metals, you must build your factory here, and we can then steal your technology," said professor Kato.
Yasuhiro Kato, an associate professor of earth science at the University of Tokyo, displays a mud sample extracted from the depths of about 4,000 metres (13,123 ft) below the Pacific ocean surface where rare earth elements were found. – Reuters
The team of scientists from Japan's Agency for Marine-Earth Science and the University of Tokyo first discovered huge reserves in the mid-Pacific two years ago. These are now thought to be 1000 times all land-based deposits, some of it in French waters around Tahiti.
The latest discovery is in Japan's Exclusive Economic Zone in deep-sea mud around the island of Minami-Torishima at 5,700 meters below sea level. Although it is very deep, the deposits are in highly-concentrated nodules that can be extracted using pressurised air with minimal disturbance off the seafloor and no need for the leaching.
Professor Kato said exploration will continue for another two years before scaling up towards production. Over 50pc of the metal in the deposit is the heavier end of the spectrum, twice the level of China's key mines and without the radioactive by-product thorium that makes the metals so hard to mine.
Japan consumes half the world's rare earth metals in its cars, electronics, and environmental industries, and has accused China of withholding supplies as a pressure tool. The country has been scrambling to find other sources under its "Strategy for Ensuring Stable Supplies of Rare Metals", but a joint venture in Vietnam that once looked promising has so far yielded only lighter rare earths.
Professor Kato said a single ship drilling in the target zone at Minami-Torishima could supply Japan's needs for a year, breaking strategic dependence at minimal cost. "We don't need to mine it intensively. All we need is enough to force China to lower its prices."
Rare earth metals are the salt of life for the hi-tech revolution, used in iPads, plasma TVs, lasers, and catalytic converters for car engines. Dysprosium is crucial because it is the strongest magnet in the world but also remains stable at very high temperatures. Neodymium is used in hybrid cars, and terbium cuts power use for low-energy lightbulbs by 40pc.
The metals are also used in precision-guided weapons, missiles such as the Hellfire, military avionics, satellites, and night-vision equipment. America's M1A2 Abrams tank and the Aegis Spy-1 radar both rely on samarium.
Washington was caught badly off guard when China started restricting supplies. The US defence and energy departments have now made it an urgent priority to find other sources, but warn that it may take up to a decade to rebuild the supply-chain. The US Magnetic Materials Association said America had drifted into a "silent crisis".
Most rare earth metals are not that rare but they are hard to find in viable concentrations, and the metallurgy is complex.
The new discovery is the second time this month that Japan has announced a major find on the sea floor. It announced a break-through in extracting gas from methane hydrates under the ocean last week, a technology that is likely to prove costly but could meet Japan's gas needs for a century.