Petratherm contracted Quantec Geoscience Pty Ltd to record the Callabonna Magneto-Telluric Survey during December 2007. The purpose of the survey was to determine the depth to basement and thus determine the potential of the area to host a geothermal resource. A total of 11 stations were recorded, spaced 500m apart in a single North-South across GEL 157. GEL 157 is located to the west of Lake Callabonna some 90 km north-east of Arkaroola. The licence covers an area of a significant gravity low – The Callabonna Gravity Low. The survey was deemed an operational and technical success with excellent data recorded. Interpretation of existing data (gravity and magnetics) had identified an interpreted granitic batholith beneath 3-5 kms of cover. It was hoped that the area may have a blanket of at least 3000m of insulating material for it to be a viable geothermal prospective area. Interpretation of the new data by ‘1D” inversion models produced conflicting results with the Bostick 1D model suggesting a basement at between 3000-3500m depth while the Occam 1D inversion model suggested depths of about 2000m. Modelling using the RLM 2D approach and the PW2D approach produced similar conflicts and a depth to basement of 2000m was favoured and accepted.