Deep-Sea DC Resistivity and Self-Potential Monitoring System for Environmental Evaluation With Hydrothermal Deposit Mining

Environmental impact assessment has become an important issue for deep-sea resource mining. The International Seabed Authority recently developed recommendations guidelines on environmental of mining effects. Several research and development groups have been organized to develop methods the seafloor sub-seafloor under “Zipangu in Ocean program,” a part Cross-ministerial Strategic Innovation Promotion Program managed by Cabinet Office Japanese government. One attempt planned long-term environment structure monitoring uses cabled observatory system. To support this plan, we began system monitor resistivity self-potential reflecting physicochemical properties ore deposits existence hydrothermal fluid. system, which mainly comprises electro-magnetometer electrical transmitter, detects spatio-temporal changes subseafloor self-potential. Because project’s policy changes, was canceled. Therefore, tried conduct experimental observation using only current transmitter voltmeter unit. Data obtained during three half months show slight overall apparent variation: as small 0.005 ?-m peak-to-peak. electrode pair closest mound shows exceptionally large electric field variation, with semidiurnal period related tidal variation. Results indicate difficulty explaining variation seawater mass migration around mound. possibility is streaming potential, i.e., fluid flow below seafloor, response tides. However, not able perform rigorous quantitative analysis, further investigation required examine whether mechanism effective. proven be capable stable data acquisition, will allow including industrial applications.