A series of survey protocol for deep sea polymetallic sulfides using not electromagnetic waves but acoustic, electromagnetic, gravity and magnetic, and geochemical methods has been proposedby Japanese national project, the Next-Generation Technology for Ocean Resources Exploration (Zipangu in the Ocean Program) launched in 2014, which enables effective and efficient explorations. The first version of the survey protocol has been made to determine the potential polymetallic sulfides areas using detailed scientific researches on their genesis. Deep sea polymetallic sulfides are produced beneath the sea floor because of the interaction between sea water and sub-bottom hydrothermal solutions driven from volcanic magma, indicating that they must be discovered at mid-ocean ridges, back-arc and arc regions, and hot spots. Recent studies further show that back-arc basins such as Okinawa Trough probably produce deep sea polymetallic sulfides bodies much larger than other regions (Tsuji et al., 2012). Some interesting topics on the survey protocol which further constrains the candidate areas, include acoustic, natural electric potential and seismic survey methods, that are 1) the shipboard Multi Beam Echo Sounding (MBES) survey that can acoustically detect hydrothermal plume including abundant CO2 for regional survey (100km2 <), 2) continuous self-potential measurements with tremendously low noise in the sea water that can identify individual sulfide deposit for semi-detailed survey (10km2- 100km2), and 3) state of the art vertical cable seismic (VCS) system which enables to delineate detailed structure of hydrothermal ore deposit body for detailed survey (< 10km2). These three methods, in combination with other geophysical and geochemical surveys, have been turned out to be effective and efficient for surveying deep sea polymetallic sulfides. Multiple types of data would be integrated into a single visualization to gain a clear view of the structure of the sulfides. Integrating core lithologies obtained via drilling with the seismic reflection structure data has been found to show the seismic velocity structure along with the extent of the polymetallic sulfides bodies.

We observed temperature variations over 10 months within a Kuroko ore (hydrothermal sulfide) cultivation apparatus installed atop a 50-m-deep borehole drilled in the Noho hydrothermal system in the mid-Okinawa Trough, southwestern Japan, for monitoring of hydrothermal fluids and in situ mineral precipitation experiments. Temperature and pressure in the apparatus fluctuated with the tidal period immediately after its installation. Initially, the average temperature was 75–76 °C and the amplitude of the semi-diurnal tidal temperature modulation was ~0.3 °C. Four months later, the amplitude of tidal temperature modulation had gradually increased to 4 °C in synchrony with an average temperature decrease to ~40 °C. Numerical modeling showed that both the increase in tidal amplitude and the decrease in average temperature were attributable to a gradual decrease in inflow to the apparatus, which promoted conductive cooling through the pipe wall. The reduced inflow was probably caused by clogging inside the apparatus, but we cannot rule out a natural cause, because the drilling would have significantly decreased the volume of hot fluid in the reservoir. The temperature fluctuation phase lagged the pressure fluctuation phase by ~150°. Assuming that the fluctuations originated from inflow from the reservoir, we conducted 2-D numerical hydrothermal modeling for a poroelastic medium. To generate the 150° phase lag, the permeability in the reservoir needed to exceed that in the ambient formation by ~3 orders of magnitude. The tidal variation phase can be a useful tool for assessing the hydrological state and response of a hydrothermal system.