A team of researchers at the University of Tokyo said Thursday they have discovered high-grade gold ore on a seabed off a remote island south of Tokyo.

The ore, collected from a hydrothermal deposit at an underwater volcanic crater off Aogashima, contained as much as 275 grams of gold per ton, a figure that is higher than usual for such deposits on land or sea in Japan, the researchers said.

The average gold content — 102 grams per ton — was also much higher than the 3 to 5 grams per ton found at most major gold mines around the world.

Many more such deposits would need to be found before a commercial mining operation could be launched, Akira Asada, a professor who led the team, said. "We hope to further investigate this area and find similar locations."

The discovery was made possible due to the development of a high-precision sonar device that surveys underwater landscapes. The team used the device between June and September last year to study a caldera located some 12 kilometers east of the islet in the Izu island chain.

Multiple hydrothermal ore deposits were discovered in the survey. Samples from one of them, gathered some 750 meters below the sea's surface, was found to be rich in gold and silver, analysis showed.

"It's an area where we can expect more (mineral) resources," said Kokichi Iizasa, a professor at the University of Tokyo.

While gold has historically been mined in Japan, the number of sites has declined over the years, and only one mine, in Kagoshima Prefecture, remains operating commercially.

The country has recently been looking to increase its access to rare metals and other natural resources from the sea floor.