Modelling the electromagnetic response of the helicopter-borne ZTEM system for vertical thin plate conductors buried below conductive overburden

A desire to reduce the need to perform forward modelling on a case by case basis has resulted in an endeavour to model the ZTEM response and produce type curves. A total of 42 models of the subsurface were analysed using the OCCAM 2D MT forward modeling code. These models investigate two types of thin-plate conductors; conductive overburden and a conductive mineralized dyke. The conductance of the target, and overburden ranged from 100,000 S to 0.01 S, and 10,000 S to 0.01 S respectively. Modelling and graphical representation of the synthetic responses allowed for the production of type curves. One type curve was created for each of the six frequencies (30 Hz, 45 Hz, 90 Hz, 180 Hz, 360 Hz, and 720 Hz) that ZTEM measures. As expected, lower frequencies were generally more effective at resolving the conductive dyke below conductive overburden to depths down to 1000 m. A steady decrease in a ZTEM response as frequency increased was usually observed. The amplitude of the tipper response generally increased with the conductance of the dyke and decreased with the conductance of the overburden. The type curves produced for each frequency ultimately represent a useful exploration tool that can be used to predict the likelihood of successful performance of ZTEM airborne surveys for conductive targets in different geological environments around the world.