Exploration Geophysics - Volume 7, Issue 3, 1976

Scale model studies may be used to determine the structure of secondary EM fields for geometries where the mathematical approach is unreasonably difficult or requires independent verification. To encompass the wide range of EM techniques used by industry and to enable realistic traverses to be simulated, a model facility of considerable physical size must be employed. Such a facility is now operational at the CSIRO Division of Mineral Physics. At a typical scale factor of 300:1 the model can simulate surface or airborne traverses over 1 km in length and borehole logs beyond 600 m in depth.

The model facility features accurate positioning of the scale sensors in three axes, computer-based traverse control and data acquisition. Target and host can be accurately simulated with a wide variety of materials. Up to four distinct conductivities can be currently used at reasonable scale factors. This is achieved with the assistance of synthetic conducting material whose conductivity can be controlled over a range to fill the gap between electrolytes and graphite. The physical size of the facility is such that reasonable scale factors and operating frequencies enable field situations to be modelled with common electrolytes and the synthetic material.

An orientation geothermal ground survey at Collie Coalfield, W.A., indicates that this method is a cheap exploration tool to detect oxidising coal seams at or near crop and the presence of fault zones.