1887
Volume 40, Issue 8
  • ISSN: 0263-5046
  • E-ISSN: 1365-2397

Abstract

Abstract

Semi-airborne electromagnetic (EM) techniques offer the opportunity to combine lightweight airborne receivers mounted on unmanned aerial vehicles (UAV) with high-moment transmitters on the ground. Owing to their low flying speed, UAVs facilitate recordings of low-frequency signals, which is beneficial for the exploration of deeply seated mineral deposits or other geological targets. However, noise from the electrical components of the aircraft as well as motional noise pose limits on the signal-to-noise ratio at far offsets from the transmitter. Here, we demonstrate the use of an optically pumped magnetometer (OPM) suspended below an UAV to measure scalar EM responses in the frequency range from 1–256 Hz that is nearly unaffected by motional noise. The responses can be identified with the component of the EM signal in the direction of the geomagnetic field, and they can be inverted into resistivity using available software solutions. We illustrate the technique using field data from the Hope deposit, Namibia. Two-dimensional inversion models image the mineralization zone with remarkable resolution from the surface to about 300 m depth, in good agreement with results from previous exploration. This field example suggests that the method is efficient for exploring conductive mineral deposits at depths of several hundred meters.

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