An all-frequency resistivity-depth and static-correction technique for CSAMT data, with applications to mineralised targets under glacial cover (Western Tasmania) and basalt cover (Victorian goldfields)

Abstract

New algorithms for apparent resistivity, static corrections, and Bostick transforms of CSAMT data allow real-time production of parasections for resistivity versus depth from profiles of CSAMT data at all frequencies. This allows rapid visualisation of 2D and 3D CSAMT model data and comparison with field data. The resulting interactive fitting of parasections of model and field data provides an alternative to formal inversion. The process is used to model the effect of glacial erosion features in CSAMT data from Western Tasmania in order to assess the sensitivity of the CSAMT method for the detection of targets such as steeply-dipping graphitic and mineralised alteration zones. The approach has advantages of real-time capability (with potential to flag data affected by cultural and power transmission line noise), of discriminating between effects of surficial conductive variations such as filled glacial erosion features, and of differentiating between genuine dipping conductors, vertical conductors, and artefacts from near-surface effects, which may generate apparent ?vertical? conductive anomalies. A similar approach using CSAMT data from basalt-covered terrain in the Victorian goldfields, combined with 3D EM modelling, was successful in identifying a prospective sulphidic conductor in the Ordovician basement, beneath variably-conductive basalt cover.