Optimizing towed controlled-source electromagnetic surveys for seafloor and embedded massive sulfides

Deep-sea massive sulfide deposits are strategically important mineral resources, driving the need for geophysical exploration technologies capable of delineating both seafloor massive sulfide (SMS) deposits exposed at the seafloor and embedded massive sulfide (EMS) deposits concealed beneath sedimentary cover. Controlled-source electromagnetic (CSEM) methods are effective for detecting low-resistivity sulfide bodies. Recent CSEM studies have imaged SMS and EMS by integrating towed systems with ocean-bottom electrometers (OBEs). However, the deployment and retrieval of OBEs are time-consuming and costly, rendering standalone towed CSEM systems attractive for rapid and continuous exploration. Numerical simulations were conducted to determine an optimal configuration for a standalone towed CSEM system. Our results demonstrate that longer source-receiver offsets (350–500 m), combined with higher frequencies (up to 5 Hz), provide an optimal baseline configuration for suppressing inversion artifacts and resolving SMS and EMS. Furthermore, measurements at shorter source-receiver offsets (100–200 m) are more sensitive to shallow SMS deposits and would therefore be advantageous to include in this configuration. Our results indicate that system sensitivity is concentrated directly beneath the towline. Consequently, resolving small-scale SMS deposits requires the system to pass directly over the target, necessitating survey-line spacing tailored to the expected target dimensions. These findings establish practical operational guidelines for the efficient exploration of marine mineral resources.