Exotic elements with names like neodymium and europium have been pulled from seawater by hydrothermal vents over millions of years and deposited on the ocean floor, Japanese geologists said.
One square area of metal-rich mud 1.4 miles wide might contain enough rare earths to meet most of the global demand for a year, the researchers report in the journal Nature Geoscience.
"I believe that rare earth resources undersea are much more promising than on-land resources," said Yasuhiro Kato, a geologist at the University of Tokyo who led the study.
About 97 percent of the globe's rare earth elements currently come from mines in China, which has been restricting exports, raising fears of shortages, ScienceNews.org reported Sunday.
Kato and his colleagues analyzed seafloor cores taken from 78 sites throughout the Pacific Ocean, and found some areas with concentrations of rare earths comparable to those found in clays mined in China.
However, deep-sea mining to extract such elements has always proven difficult because of high costs and environmental concerns, some experts say.
"I don't understand how this can be expected to be an economic way to recover rare earth," said Daniel Cordier, a mineral commodity specialist at the U.S. Geological Survey's National Minerals Information Center in Reston, Va.