We continue to investigate an ancillary method to Induced Polarization for sulphide exploration, using analysis to measure heterodyne effects in time-domain Airborne Electromagnetic data. We investigate how a parameter named mixabiity can characterise these effects in terms of frequency content and composition, finding that with sufficiently low noise levels, heterodyne effects could theoretically be observable in time-domain AEM data. Analysing existing AEM survey data, we earlier found no spatial correlation between known sulphide distribution and mixability. We postulated that this is because potential heterodyne effects due to sulphides were being masked by two different limitations of the survey dataset we used; firstly, variable transmitter waveform asymmetry; and secondly, the decreasing signal levels from the fixed a ground-loop transmitter resulting in increasing relative noise levels away from the transmitter. We therefore conducted a airborne Slingram EM/IP survey with the BIPTEM system to address the identified limitations of existing test data. We present results from an airborne test at Kempfield, the test site for definitive ground tests of the heterodyne method for sulphide detection. The small mixability anomalies detected in the airborne data were not consistent with either drilled sulphides or mapped IP anomalies.

Open-Access Online Publication: November 3, 2023