Electromagnetic signatures of deep-sea massive sulfide deposits

Deep-sea hydrothermal vent fields associated with the formation of seafloor massive sulfides (SMS) may become a future source of high-tech minerals such as Cu, Ni, Pb, Co, and REE, which are all in demand for the energy transition away from hydrocarbon resources. The identification and evaluation of the deposits in the deep ocean is a needle in a haystack problem. They are relatively small (size of a soccer field) and form in complex terrain at mid-ocean ridges, island arcs and back-arc spreading centres. Active hydrothermal vents are often accompanied with black smokers and have an abundant, environmental sensitive fauna and low mineral potential. Inactive and extinct vent sites are generally missing characteristic seafloor expressions and distinct vent fauna, and may be hidden under a thin layer of sediments. Thus, video observations and sampling may not be sufficient to evaluate the size and spatial extent of the SMS deposit. Massive sulfides are known to belong to the group of natural rocks with the highest electrical conductivity due to their electronic surface conduction, which makes them an interesting target for electromagnetic and electrical methods. BGR’s GOLDEN EYE electromagnetic deep-sea profiler has been developed to collect a variety of marine frequency domain CSEM loop data and electric dipole-dipole data in the German license areas for SMS exploration located in the Indian Ocean. The data are analyzed in terms of frequency, thus depth-depending conductivity models, chargeability and self-potential effects. The latter has been also measured with two deep-towed Vulcan E-field receivers. Both systems reveal significant anomalies over visually identified sulfide targets, but also in so far uncovered areas. We present details on instrumentation, data analysis, and preliminary results from resent cruises.