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

Abstract

We study a new marine electromagnetic configuration that consists of a ship‐towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor. The approach was tested at the Palinuro Seamount in the southern Tyrrhenian Sea, at a site where massive sulphide mineralization has been previously identified by shallow drilling. A 3D model of the Palinuro study area was created using bathymetry data, and forward modelling of the electric field diffusion was carried out using a finite volume method. These numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to ∼100 m away when the transmitter is located directly above the target. We also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone, the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few tens of metres. Furthermore, the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry. As a horizontal transmitter is logistically easier to deploy, we conducted a first test of the method with a horizontal transmitter. Apparent conductivities are calculated from the electric field transients recorded at the remote receivers. The analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone. Forward modelling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling. Our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulphide deposits.

Inactive Sulfide Ecosystems in the Deep Sea: A Review

“…Investment is also being made in detailed geospatial analysis of geological features to develop probabilistic maps of favorable prospective regions of mid-ocean ridges (Ren et al, 2016;Juliani and Ellefmo, 2018). New seismic (Asakawa et al, 2018) and electromagnetic (Schwalenberg et al, 2016;Müller et al, 2018;Safipour et al, 2018) tools are being developed and tested to detect sulfides in the absence of physico-chemical water column anomalies, even when buried beneath 10's of meters of sediment. Future avenues of sub-sediment exploration may include gravity coring and shipboard analysis of metals in sediments together with AUV-based self-potential, electromagnetic, hyperspectral, and bathymetric mapping that might be used to locate sulfides as much as 20-km off-axis (Petersen et al, 2017(Petersen et al, , 2018Dumke et al, 2018).…”

Marine DC resistivity and self-potential survey in the hydrothermal deposit areas using multiple AUVs and ASV

“…Asakawa et al (2016) and Nakayama and Saito (2016) developed a TEM system of a horizontal coincident-loop and a magnetometer, which are towed below a remotely operated vehicle (ROV). Safipour et al (2018) proposed a new marine EM system using a TEM transmitter and ocean-bottom electro-magnetometers (OBEMs) deployed to the seafloor as receivers. They successfully detected seafloor massive sulfide deposits.…”

Internal Structure of a Seafloor Massive Sulfide Deposit by Electrical Resistivity Tomography, Okinawa Trough

“…Some new equipment has been designed for the near-seafloor resistivity mapping but with limited penetration depth of less than several meters (Kowalczyk, 2008). Other new surveys have deeper penetration to tens to hundreds of meters (Constable et al, 2018;Imamura et al, 2018;Müller et al, 2018;Safipour et al, 2017;Safipour et al, 2018). However, the measurements should be done as stationary (with the fixed source, receivers, or both) lacking dense spatial samplings.…”