b'Michael Astens best of Exploration GeophysicsFeatureAnalysis of the geophysical data However, the data was good enough to interpret a continuous body from 10300N to 10700N, plunging to the north and open The ability of UTEM to detect the Hellyer deposit where IP,in this direction.airborne EM (McPhar H400), and Max Min had failed (Eadie & Silic 1984), shows well the power of fixed loop, time domainIn spite of the fact that the anomaly on 10700N continued to EM systems. The three most critical lines of UTEM verticalthe later time of at least 4 ms, the first drill hole was located component data are shown in Figs 2, 3 and 4. on 10400N (Fig. 5), the reasoning being that the target was shallower on 10400N and there was no chance of the data being The feature that inspired the extension of the grid to the northinfluenced by the encroaching shales as there was on I0700N is seen at station 5675E on 10300N (Fig. 2). This anomaly, which(Fig. 6), thus enabling a more precise interpretation. The first was interpreted to be from a deep, conductive body, is apparenthole of the drilling programme, HL 3, successfully intersected in the data from 0.2 to 2 ms. The fact that the anomaly lasted untilthe target, as did the third hole, HL 5, on 10700N.2ms made this by far the most conductive feature on the grid.Figures 3 and 4 display the results from Lines 10400N and 10700N, respectively. The amplitude of the response is much lower on these follow up lines than on 10300N because:(1)the second transmitter loop was located to be maximum coupled with the expected vertical body and ended up being almost totally null-coupled with the actual flat-lying body;(2)there is less enhancement due to current channelling because the second loop is much closer to the targetconductor.Figure 5:Geological section 10400N.Figure 3:Vertical component UTEM data on line 10400N, the first line drilled.Figure 6:Geological section 10700N.AcknowledgmentsThe authors would like to acknowledge Gary McArthur, Supervising Geologist, Hellyer, for his excellent work and for preparing the geological cross sections. We would also like to acknowledge Aberfoyles management, in particular Max Richards, Hugh Skey and John Sise for the inspiration and support they supplied throughout the exploration period, Guido Staltari of GEC for continual geophysical discussions Figure 4:Vertical component UTEM data on line 10700N. in the planning and interpretation process, and the staff of 51 PREVIEW AUGUST 2020'