Electromagnetic experiments for the detection and characterization of seafloor massive sulfides at the Palinuro Seamount

Seafloor massive sulfides (SMS) are regarded as a potential future resource to satisfy the growing global demand of strategic metals. Aside from mining and retrieving profitable amounts of massive sulfides from the seafloor, the present challenge is to detect and delineate significant SMS accumulations, which are generally located near mid-ocean ridges and along submarine volcanic arc and backarc spreading centers.In the past years we have used the marine transient electromagnetic induction system MARTEMIS, a coincident-loop TEM system developed at GEOMAR (Kiel, Germany), in various marine geological settings for the detection and characterization of SMS in the shallow seafloor down to a depth of ~30m. The system was also used in combination with remote EM receivers (Coil2Dipole experiment) to allow for investigations of conductive structures,which are covered by up to ~100m of sediments.During two research cruises (2015: POS483, 2017: POS509), several types of EM experiments were carried out at the Palinuro Seamount located about 141km to the SSE of Naples (Italy) in the Tyrrhenian Sea. At this hydrothermally practically inactive site, previous investigations had confirmed the occurrence of SMS by drilling down a depth of 5m, the maximum depth reached by the drill (BGS Rockdrill I). For all EM experiments we used the marine transient induction system (MARTEMIS) -a mobile marine coil system -as source. For TEM experiments a coincident loop receiver integrated into the MARTEMIS system was used to investigate the shallow conductivity structure of the seafloor down to a depth of about 30m. In the TEM experiments we were able to show that the lateral extent of the SMS body is larger than previously known from drilling. In a second set of experiments, which we have named "Coil2Dipole", we used remote OBEM (ocean bottom EM) receivers to measure theelectrical fields excited by the MARTEMIS coil source. In this experiment, OBEM receivers were able to detect the transmitted signal up to distances of about 250m, which yields an increased penetration depth of about 120m as compared to the TEM experiment. A first evaluation of the OBEM data indicates a conductor to the SW of the known mineralization at greater depth, which we interpret as the mineralized feeder channels to the known SMS site