Successful Visualization of the Two-Story Distribution of Seafloor Massive Sulfides (Ishizu et al., 2019, GRL)

Tue, 01 Jan 2019 00:00:00 +0000

Ishizu, K. Goto, T., Ohta, Y., Kasaya, T., Iwamoto, H., Vachiratienchai, C., Siripunvaraporn, W., Tsuji, T., Kumagai H. and Koike K. (2019). Internal structure of a seafloor massive sulfide deposit by electrical resistivity tomography, Okinawa Trough. Geophysical Research Letters, 46(20), 11025-11034.

Point 1: Successful visualization of the “two-story” distribution (upper and lower deposits) of seafloor massive sulfides

Point 2 (Most Important): Elucidation of a new development mechanism for lower deposits

Seafloor massive sulfides (SMS) are next-generation metallic resources containing rare metals and precious metals. These deposits are confirmed to exist in areas with hydrothermal circulation on the seafloor. In Japan, SMS deposits have been discovered in the Okinawa Trough and the Izu-Ogasawara regions. However, their subsurface distribution and development mechanisms were previously unknown. This paper details the visualization of SMS distribution in the Iheya hydrothermal field of the Okinawa Trough using a marine electrical resistivity tomography system where both the transmitter and receivers are towed on a cable. Marine electrical exploration works like a dowsing machine by injecting electricity into the seafloor and estimating areas with high electrical conductivity (i.e., where metallic deposits exist). Put simply, it’s like a treasure-hunting machine that allows us to obtain information below the seafloor without drilling.

The marine electrical exploration device used in this study utilized 10 receivers on the cable to significantly increase the amount of data collected (conventional devices typically use 5 or fewer). This increased data volume allowed for detailed subsurface imaging down to about 60m. From this detailed map, we revealed that SMS deposits exist not only on the seafloor (upper deposit) but also at a depth of about 30m (lower deposit), a highly novel finding. By integrating this detailed subsurface map with drilling data, we proposed a new development mechanism for the lower deposit: hydrothermal fluids are cooled below a cap layer, causing metallic components to precipitate and form the deposit beneath the cap. This is the most significant novel point of this paper.

Press release articles can be read here:

Seafloor Massive Sulfides | Keiichi Ishizu

Successful Visualization of the Two-Story Distribution of Seafloor Massive Sulfides (Ishizu et al., 2019, GRL)

Point 1: Successful visualization of the “two-story” distribution (upper and lower deposits) of seafloor massive sulfides

Point 2 (Most Important): Elucidation of a new development mechanism for lower deposits