LAUSR

Seafloor Massive Sulfide (SMS) deposits contain abundant metals such as Cu, Zn, Au and Ag, which are of growing economic interest. Currently, we need a geophysical method to rapidly obtain the 3D structure of such SMS deposits for resource assessment. We report here a self-potential survey performed with an autonomous underwater vehicle (AUV) at the Yuhuang hydrothermal field on the ultraslow-spreading Southwest Indian Ridge (SWIR) with a water depth ranging from 1300 to 2200 m. The electric field sensors are attached to the tail of the AUV to record the electric field ∼50 m above the seafloor. The electric field strength is observed to reach an amplitude of 0.6 mV/m at this known SMS deposit. Self-potential tomography is used to obtain the 3D structure of the ore deposit at this site and benchmark tests are first performed on synthetic cases to determine the best algorithm in terms of ore localization. The 3D self-potential tomography reveals a South-sloping ore body, which is 100 m-long in the north-south direction and nearly 200 m-long in the East-West direction. The vertical extent of the ore body is about 100 m. These results suggest that an AUV-based self-potential survey and tomography is a useful exploration method to characterize the geometry of SMS deposits. This method may play an important role in the future resource assessment with other geophysical methods such as magnetic and induced polarization measurements.