Radio frequency tomography trial at Mt Isa Mine

A cross-hole RFEM (Radio Frequency Electromagnetic) tomographic survey was conducted at the Mt. Isa Copper Mine in 1995 as part of a CMTE/AMIRA project investigating the application of geophysics in metalliferous mines. The primary objective of the survey was to evaluate the capability of RFEM for orebody delineation, in a section of the mine where a correlation had previously been established between conductivity and copper grade. An absorption tomograrn constructed from the limited 52.5 kHz data set demonstrated that RFEM has potential in this environment for resolving orebody boundaries and establishing ore continuity between drill holes. The calculated absorption coefficients on the tomogram lie between 0.94 and 5.165 dB/m, consistent with laboratory absorption measurements on rock samples from the survey site. The continuity of the footwall orebody, paralleling the Paroo Fault, was not well represented in the tomogram, due to low ray coverage in the corner of the image. However, a simple amplitude mask, depicting only the less attenuated ray paths, provided evidence for continuous ore between the holes. This provides encouragement for efforts to combine amplitude masking with tomography.

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