Self-potential investigation of a deep-sea polymetallic sulfide deposit at the Southwest Indian Ridge (Indian Ocean)

Abstract

Deep-sea polymetallic sulfides formed by hydrothermal activity are considered a potential resource for economically valuable base and precious metals.The Southwest Indian Ridge (SWIR, Indian Ocean) hosts active and inactive hydrothermal systems. Inactive hydrothermal fields are more abundant but difficult to characterize. We report a self-potential investigation to locate inactive ore deposits at the Yuhuang hydrothermal field on the ultraslow-spreading SWIR. A horizontal array of 6 AgCl electrodes were attached to a dual towed transient electromagnetic system to record the electrical field at a height of 40 m above the seafloor. The observed electrical field strength near the known sulfide drills reaches 0.5 mV/m. Negative self-potential anomalies (~ -25 mV, obtained by integrating the electrical field) were observed. High electrical conductivities (up to 12 S/m) of sulfide samples measured in the laboratory and the oxidize sulfides recovered at the outcrop of the deposit suggest that the selfpotential anomalies are due to sulfides mineralization and corrosion of the polymetallic sulfides. Tomography of the self-potential anomalies reveals a localized current source distribution with a thickness of ~65 m. Our field data demonstrate that the self-potential method is a useful exploration method to characterize seafloor sulfides localized in inactive hydrothermal fields at mid-ocean ridges.