By analyzing the piston core samples, the research group found that rare earth-rich mud whose quality is equivalent to that of the ion adsorptive ore deposit in southern China exists in a wide area of the Pacific Ocean. Ion adsorptive ore deposits are formed when rare earths adsorbed by clay minerals concentrate on soil made of weathered granite.
They were found only in southern China such as Jiangxi and Hunan provinces. They contain large amounts of heavy rare earths including dysprosium and terbium, and most of the rare earths can be extracted just by using dilute acid to leach them out.
According to the results of the analysis of the whole-rock chemical compositions, there are rare earth-rich mud with an average thickness of 8.0m and an average gross rare earth density of 1,054ppm in the southeastern Pacific Ocean and mud with an average thickness of 23.6m and an average gross rare earth density of 625ppm in the central Pacific Ocean.
If rare earth-rich mud is exploited in a 4km2 area (depth: 10m) at "Site 76," which is located in the southeastern Pacific Ocean, it will potentially provide an amount of rare earths equivalent to the amount consumed in Japan in one or two years. In addition to rare earths, it contains concentrated amounts of rare metals such as vanadium, cobalt, nickel and molybdenum, the research group said.
Most of the newly-found mineral resources are located in the high seas. But it is possible for Japan to obtain mining areas if it meets some conditions such as an agreement with the International Seabed Authority (ISBA).
Though the mineral resources are distributed 3,500 to 6,000m below the surface of the sea, it is possible to mine and collect more than 40 million tons of rare earth-rich mud every year with existing technologies, Kato said. And rare earths can be extracted from the collected mud in a short time by using, for example, dilute sulfuric acid.