A self-potential investigation of submarine massive sulfides: Palinuro Seamount, Tyrrhenian Sea

Abstract

The self-potential (SP) method detects naturally occurring electric fields which may be produced by electrically conductive mineral deposits such as massive sulfides. Recently, there has been increasing interest in applying this method in a marine environment to explore for seafloor massive sulfide (SMS) deposits which may contain economic resources of base and precious metals. While SMS sites that are associated with active venting and are not buried under sediment cover are known to produce an SP signal, the effectiveness of the method at detecting inactive and sediment-covered deposits remained an outstanding question. We built an instrument capable of recording SP data in a marine setting. We carried out a test of the instrument at the Palinuro Seamount in the Tyrrhenian Sea. Palinuro is one of only a few known sites containing an SMS occurrence which is buried under sediment and not associated with active hydrothermal venting, although diffuse seepage of hydrothermal fluids is known to occur at the site. Elevated electric field strengths recorded in and near the site of previously drilled massive sulfide samples are on the order of 1-3 mV/m. A second zone of high field strengths was detected by us to the north of the drilling area where gravity coring later confirmed the existence of massive sulfides. Our observations indicate that an SP signal can be observed at the site of SMS mineralization even when the mineralized zone is shallowly buried and active hydrothermal venting is not present. These observations could aid in the planning of future marine research expeditions which use the SP method in the exploration of seafloor massive sulfides.

Self-potential mapping using an autonomous underwater vehicle for the Sunrise deposit, Izu-Ogasawara arc, southern Japan

“…Less active systems might require lower survey altitudes (approx. 5-10 m) (e.g., Heinson et al 1999Heinson et al , 2005Safipour et al 2017).…”

“…In these active surveys, self-potential signals are obtained as fluctuations in the baseline that might be removed as noise. To obtain self-potential signals from the data of these active surveys, the data should be averaged over a cycle of the active source signal because the cycle comprises an alternating negative and positive current source pair (e.g., Constable et al 2018;Safipour et al 2017). Using data obtained from these active surveys, a self-potential signal is useful as a quick-look tool.…”

“…The self-potential method is particularly efficient in marine environments because towing two or more non-polarized electrodes reveals in situ electrostatic fields. Although this method is not used very commonly in marine environments at present, it has been investigated continually since the 1970s (e.g., Beltenev et al 2009;Brewitt-Taylor 1975;Cherkashev et al 2013;Constable et al 2018;Corwin 1976;Francis 1985;Heinson et al 1999Heinson et al , 2005Kawada and Kasaya 2017;Petersen and Shipboard Scientific Party 2016;Safipour et al 2017;Von Herzen et al 1996). The use of autonomous underwater vehicles (AUVs) greatly improves the efficiency of the self-potential survey (Constable et al 2018;Sato et al 2017).…”

A first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers: Palinuro Seamount, Tyrrhenian Sea

“…(c)); when the mean absolute difference between modelled apparent conductivity Z score and data are calculated, the minimum value of 0.471 occurs when the conductive target is extended southward by 40 m. This suggests that the mineralization at Palinuro extends to the south of the drilling zone by a few tens of metres, which is consistent with the footprint of the self‐potential signal measured at the mineralized zone (Safipour et al . ). In addition, this southward extension of mineralization is also consistent with heat flow measurements taken of the seafloor sediment during the POS509 research cruise in February 2017, which found elevated temperatures of up to 35.6°C extending southward of the drilling zone by ∼35 m (Hölz ).…”

“…Gravity, magnetic, sonar backscatter reflectivity, and detailed bathymetry data had previously been collected over the area of the sulphides (Caratori Ligi et al 2014). In addition, during the POS509 research cruise in February 2017, a self-potential experiment detected high natural electric field strengths over the massive sulphide mineralization (Safipour et al 2017a), and heat flow data collected at the site indicated elevated seafloor temperatures over the known mineralization and extending ∼35 m southward. Electromagnetic methods had not been tested at Palinuro prior to these cruises.…”