Study on Mining System for Seafloor Massive Sulfide Mound and Results of On-Site Excavation Tests in Okinawa Trough

Japan Oil, Gas and Metals National Corporation (JOGMEC) has started an exploration program for Seafloor Massive Sulfides (SMS) in the EEZ of Japan, and launched investigations on mining and processing technologies for SMS and studies for environmental impacts caused by SMS developments. With regard to the mining technologies, the studied mining system for SMS consists of three units: which are mining tools working on seafloor, riser and lifting systems, and production support vessels with unloading facilities onto shuttle ships. Physico-mechanical characteristics of the seafloor sulfides, which are key parameters for designing mining systems, have not fully clarified yet to apply for design purposes. Because exploration campaigns and geological characterizations are still undergoing. However, two types of mining tools for testing on seafloor were developed as the mining unit. Excavation tests on the actual SMS site with the depth of 1,600m in the Okinawa Trough, south-west of Japan, were conducted in 2012. Functions of the mining tools, such as cutting abilities for seafloor sulfides, moving and maneuvering performances, and climbing capabilities on slopes steeper than 25 degrees were examined in the tests. This paper describes the outline of the proposed mining system and mining tools for SMS, as well as the results of on-site subsea mining tests in the Okinawa Trough.