RV POSEIDON Fahrtbericht / Cruise Report POS509 - ElectroPal 2: Geophysical investigations of sediment hosted massive sulfide deposits on the Palinuro Volcanic Complex in the Tyrrhenian Sea, Malaga (Spain) – Catania (Italy) 15.02.-03.03.2017

At present, investigations of submarine massive sulfides (SMS) are mostly limited to active systems due to the available methods and technologies, which rely on the detection of water column anomalies (tempera - ture or chemical tracers) and the study of seafloor's morphology. They fail to detect sites where hydrothermal activity has ceased and former landmarks such as black smokers have been eroded or are covered by sediments. During RV Poseidon cruises POS483 (“ElectroPal”) and POS484 (”MARSITE”) we have successfully collected EM and airgun seismic data over an inactive and sediment covered SMS site at Palinuro, which had previously been found by chance in 1986 and was drilled to 5m depth during research cruise M73/2. EM measurements, carried out with the novel system MARTEMIS1, not only showed high conductivities in the vicinity of the SMS deposit, but also revealed a second anomaly, possibly a zone of buried mineralization at greater depth. During cruise POS509 previous measurements were continued and extended to get a full areal coverage of the structure to fully delineate and characterize the SMS sites. EM investigations were accompanied by measurements of the ambient electrical field (→ selfpotential (SP)) and additional geophysical (heat probe) and geological (gravity core) measurements for ground truthing and further structural insight. The combination of experiments proved to be convenient in terms of handling on the ship, as EM experiments on the one hand and measurements with heat probe and gravity coring on the other hand were performed in an alternating manner each other day. This alternating style of experiments gave each method time for adjust - ments and repairs as well as time to take a first look at results so that following investigations could be directly aimed at a specific target. As an example, an anomaly detected in the SP measurements in the NNW was used to guide the last gravity coring, which then found sulfide muds in an area where sulfides were previously not expected