b'2.5D AEM inversionFeatureFigure 6.Line 16101 2.5D inversion, Z component-only, (top) and CDI (bottom) showing the location and geometry of conductive anomalies. The colour stretches are roughly equivalent; the CDI units are conductivity in Siemens/m and the 2.5D inversion units are log conductivity in milli-Seimens/m.grey-pink striped colours in Figure 4), which is host to the Dugald River deposit. These shales wrap around the Knapdale Quartzite core.Comparison of AEM inversion resultsThe log conductivity results for 2.5D, Z component-only, and CDI inversions for Lines 15701 and 16101 across the Quamby/Dugald River subset are shown Figures 5 and 6.The 2.5D inversion results show synclinal features with dips that closely match the known geology from drilling and surface mapping. Conversely, the CDIs show anticlinal patterns caused by difficulties handling strong lateral resistivity contrasts and a breakdown of the 1D assumption in the presence of steeply dipping complex geology.Interactive views of channel data misfits, the noise model and conductivity section for line 16101 (Figure 7) enable the user to validate the inversion results in this folded synclinal slate horizon example. Observed profiles are in colours and the predicted profiles are in black. The noise model panel (bright green and blue) shown below the three Figure 4.Quamby 1:100 K geology (Wyborn 1997) showing the conductiveprofile panels in Figure 7 is a by-channel (Y axis) map of shale horizons. Mapped synclinal features are highlighted by red symbols andthe noise estimates used in the inversion. Channel values inverted VTEMTMPlus lines are in blue. in blue are below the chosen noise threshold and channel values in red are negative transients assigned as IP effects. The former are down-weighted and the latter are ignored during the inversion.Managing IP effects in 2.5D inversionsThe eastern end of line 15701 displays a CDI artefact, which is interpreted as being caused by near surface IP effects in this area (Figure 5). These IP effects manifest as negative late time transients as seen in the profile displays and highlighted in red in the noise panel in Figure 8. The source of the IP effects has not been investigated in the field, but these effects are often associated with near surface clays.A joint Z component-only inductive and IP inversion was run Figure 5.Line 15701 2.5D inversion, Z component-only, (top) and CDIover this line, and the results are presented in Figure 8, where it (bottom). The colour stretches are roughly equivalent; the CDI units areis compared with a Z component-only inductive inversion. The conductivity in Siemens/m and the 2.5D inversion units are log conductivity inred zones in the accompanying noise map highlight the time milli-Seimens/m. gates and areas with negative transients.35 PREVIEW AUGUST 2020'