Abstract
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.