The research team — comprised of several universities, businesses and government institutions — surveyed the western Pacific Ocean near Minami-Torishima Island, Japan. According to the study, the findings have "tremendous potential" to be a source of rare-earth elements.
In a sample area of the mineral-rich region, the team's survey estimated 1.2 million tonnes of "rare-earth oxide" was deposited there. The survey was conducted jointly by researcher with Waseda University Yutaro Takaya, and Yasuhiro Kato of the University of Tokyo, among others.
Technology Metals Research LLC founding principal Jack Lifton, who wasn't involved in the research, told The Wall Street Journal "this is a game-changer for Japan".
"The race to develop these resources is well under way," he said.
The finding extrapolates that a 2500sq km region off the southern Japanese island should contain 16 million tonnes of the valuable elements, and "has the potential to supply these metals on a semi-infinite basis to the world".
The area's reserves offer "great potential as ore deposits for some of the most critically important elements in modern society," it said.
The report said there were hundreds of years of reserves of most of the rare-earth elements in the area surveyed. Extracting them would likely be costly, but resource-poor Japan is pushing ahead with research in a bid to gain more control over next-generation technologies and weapon systems.
China currently holds a tight grip on the rare-earth minerals market with Beijing controlling about 95 per cent of global rare-earths production as of 2015, according to CNN. Because of this, Japan and other countries rely on China to set prices and availability.
But Beijing has severely restricted exports of these products at times of diplomatic tension.
In 2010, for example, Japanese manufacturers faced serious supply shortages as China limited the valuable exports.
That came after Japan arrested the captain of a Chinese trawler that was involved in a run-in with Japanese coastguards near the disputed Senkaku Islands, claimed by China as the Diaoyus.
The study team has developed an efficient and economic method to collect the deep-sea mud that separates valuable elements from others in the mud.
"The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new (rare-earth rich mud) resource could be exploited in the near future," the study said.
The US Department of Energy and the European Union has previously issued warnings about shortages of rare-earths as China's own consumption of them increases.
Lifton, whose company consults for technology firms and investors interested in rare-earth metals, said there were also cobalt and nickel-bearing deposits on seabeds near Australia and New Zealand, the WSJ reported.