Resistivity survey of seafloor massive sulfide areas in the Iheya north area, off Okinawa, Japan

Abstract

The recent growth of world-wide requirement of metals demands advanced explorations for finding metal mineral deposits. On the basis of the feasibility studies, we developed instruments for the marine DC resistivity survey system attached on a remotely operated vehicle(ROV). We conducted to image the shallow resistivity structures around the submarine massive sulfide (SMS) deposits located off Okinawa, southwest of Japan. ROV Hyper-Dolphine (HPD), JAMSTEC, was used for the marine DC resistivity survey. A transmitter, a voltmeter and a vertical electrode array with length of 10m were loaded on HPD during the dive to the seafloor. The sounding depth with this survey configuration was less than about 5m based on the numerical simulations. One-day operation around the SMS gave us the marine DC resistivity survey at about 20 sites The obtained apparent resistivity is moderately low at the most of sites, but is extremely low around the SMS area with hydrothermal chimneys. Also, the surface heterogeneity of resistivity is obvious around the vents area. On the basis of comparison between our results and geological features and heat flow measurements, we conclude that the conductive features around the chimney area could be explained by conductive SMS and/or hydrothermal fluid with high conductivity. Thus, the marine DC resistivity survey with ROV is effective to interpret the seafloor features around the SMS.