b'2.5D AEM inversionFeatureFigure 24.Late time correlated noise before (top) and after (bottom) lateral smoothing.Summary All of the 2.5D inversion products generated by the Intrepid CDI or 1D inversions are well-established processing strategiessoftware come with information on reliability through the delivery for AEM data. Experienced users have learned how to recogniseof survey and predicted profile misfits at survey resolution.and manage some of the shortcomings of these inversions, andThe Quamby/Dugald River and Kevitsa examples demonstrate appear to be reluctant to change their practice. However, CDIsthat 2.5D inversion products can be used confidently by or 1D inversions can mislead geologists and/or less experiencedgeologists and geophysicists for orebody targeting and users and, as a consequence, result in poor exploration outcomes. for geological and structural mapping in plan as well as in The 2.5D AEM inversion technology developed by Intrepidcross section. These products also facilitate the integrated produces very clean and spatially accurate images of subsurfaceinterpretation of AEM, magnetics, gravity and surface geology.conductivity in both cross section and in plan (with some postThe Elura example demonstrates that 2.5D forward modelling is an processing) that are mostly free from the problems often seen ineffective tool that can assist with the analysis of target detectability CDI and 1D inversionsparticularly where 1D assumptions arewhen the explorer is in the AEM survey planning phase.not met.Older AEM survey data and/or data acquired in areas with 2.5D inversions are much less computationally expensive thanconductive cover or other forms of geo-electrical noise (e.g. IP 3D inversions, and not limited by line spacing. effects) can, however, present problems that require experience 2.5D inversions can be performed on data from all of theand appropriate analytical tools to manage.common AEM systems and at survey scale on lines of 100 kmRaising awareness of new technologies and encouraging their in length. Constrained inversions are also an option if there isacceptance can be a challenge for geophysicists working in adequate information about the geo-electrical section. exploration. Hopefully this article has gone some way towards AUGUST 2020 PREVIEW 46'