Semi-airborne electromagnetic exploration of deep sulfide deposits with UAV-towed magnetometers - Part 1: Processing Modeling

In recent decades, global technological expansion, alongside significant shifts in information technology, energy supply and mobility, has dramatically increased the demand for certain raw materials, especially minerals. To meet future demand, new strategies and solutions are being sought. Semi-airborne electromagnetics, as an emerging method to sense conductive subsurface structures, holds high potential for mineral exploration and can be applied to uncover untapped ore deposits or re-evaluate exploited ones. This technique has been successfully implemented in multiple studies and is a core part of the DESMEX (Deep Electromagnetic Sounding for Mineral Exploration) joint project. To date, promising sites are being surveyed either employing crewed aircraft or using ground-based methods, both of which come with limitations concerning site access, survey period, achievable resolution and cost. By utilizing uncrewed aerial vehicles (UAVs) some constraints and expenses can be overcome. Taking advantage of a battery-powered 25 kg maximum takeoff weight octocopter and two complementary magnetometers, an optically pumped total-field magnetometer and an induction coil triple, we have surveyed the Hope deposit, a known, unexploited massive sulfide mineralization in Western Namibia. Time-varying electromagnetic fields, excited by grounded electric-dipole transmitters, were measured and evaluated discretely in frequency domain. Based on two-dimensional inverse modeling, we were able to image the Hope ore body and to trace it down to a depth of more than 300 m. Combined sensor data inverted along adjacent profile lines reveal an imposing, contiguous dipping conductor that can be clearly assigned to the Hope structure. To assess the significance of our results, we inverted data from the two sensor systems individually as well as jointly and carried out detailed modeling studies. Our findings are supported by available resistivity models based on audio magnetotelluric data and yield an excellent match to existing borehole probes.