Paterson AEM Survey EM Vision 3D Inversion Data and Release Notes: Kintyre area

Conductivity-depth estimates generated using the 1D Geoscience Australia layered earth inversion algorithm (GA-LEI) have been released to the public domain. The GA-LEI has been shown to provide useful mapping of subsurface conductivity features in the Paterson; for example paleovalleys, unconformities and faults. GA-LEI interpretations have been supported by independent borehole conductivity logs, and lithological drill-hole information. The Geoscience Australia Record 2010/12; Geological and energy implications of the Paterson Province airborne electromagnetic (AEM) survey, Western Australia, summarises the AEM processing, inversion, interpretation and implications for mineral exploration using the 1D GA-LEI. There is an inherent assumption in the GA-LEI algorithm that the earth can be represented by a set of 1D layers, which extend to infinite distance in the horizontal plane. This layered earth assumption has some limitations, and has been demonstrated to create artefacts when applied to heterogeneous 3D geological features. 3D inversion methods can potentially overcome some of the limitations of 1D inversion methods, reducing the artefacts of a 1D earth assumption. 3D inversions require much greater computational resources than 1D methods because they have to solve many large systems of equations. In addition, a large sensitivity matrix is computed, which increases memory requirements, and the process must be repeated for multiple iterations. This computational expense has generally limited the application of 3D inversions to AEM datasets, and restricted its practicality as a general mapping tool. The EMVision® inversion generated by TechnoImaging presents a method of running a 3D inversion, with a runtime comparable to 1D inversion methods. The EMVision® algorithm uses a moving footprint to limit the number of data points needed as input to the inversion at any one location. A background conductivity model is chosen to represent the far-field response of the earth, and the data points within the AEM footprint are treated as anomalies with respect to the background. In 2010, Geoscience Australia decided that a comparison of the GA-LEI with the EMVision® inversion would be useful both for geological interpretation and for assessing the benefits of 3D inversion of AEM. A subset of the regional Paterson AEM dataset around the Kintyre uranium deposit was provided to TechnoImaging to create a 3D inversion using EMVision® software. The data subset was a combination of GA data and data owned by Cameco Corporation and the cost of inversion by TechnoImaging was shared by both parties. Under the terms of the agreement between Cameco Corporation and Geoscience Australia there was a moratorium on the data release until 2012.