Marine deep-towed self-potential and DC resistivity explorations for seafloor massive sulfide deposits

Abstract

For exploration of seafloor massive sulfide deposits, we improved the marine deep-towed electric exploration system which could be handled by vessels of private companies. The survey was conducted at the “Hakurei-site” and “Gondou-site”. At each site, clear spatial changes in the horizontal electric field, which may be due to the Self-Potential (SP), were observed. If the horizontal electric field is spatially integrated, it becomes a potential, but in reality it is not easy to integrate because of the noise of towing and the nonlinear drift of the electrodes. The polarity of the horizontal electric field varies depending on the direction of travel. Therefore, in this study, we show a method to convert a horizontal electric field into a pseudo vertical electric field with the same polarity as the potential by the Hilbert transform, and apply it for mapping the acquired data. On the other hand, in the signal processing of resistivity exploration, a method for removing short period noise relatively easily from a record after removing long period signals is shown. And it was applied to the resistivity analysis. As a result, the sub-seafloor resistivity lower than the seawater value tends to be found in the region where the pseudo vertical electric field was negative. Drilling surveys were conducted at both sites, confirming that the negative anomalies in the pseudo vertical electric field corresponds to the presence of a sulfide layer. This proves that this method is very effective in narrowing down the target areas of a Seafloor Massive Sulfide deposit.