PRELIMINARY ECONOMIC EVALUATION OF DEEP-SEA REE MUD MINING

Deep-sea rare-earth element-rich mud (REE mud) distributes in pelagic clayey sediment column on ocean seafloor at 4,000-6,000 m deep. The thickness ranges 5-80 m and the burial depth 0-100 m. The REE contents range 600-2,250 ppm in the Pacific and one of the richest, maximum 6,500ppm, has been found near Minami-Tori-shima (Marcus Is.) in Japan's exclusive economic zones. Assuming a conventional hydraulic excavation and lifting methods, the economy of REE mud mining near Minami-Tori-shima (Marcus Is.) is preliminary examined. Because the contents of valuables in REE mud are low and the ones of wastes are high, quite little chance for the economically feasible mining has been found from the result.