B-field probes for downhole magnetometric resistivity surveys

The downhole magnetometric resistivity (DHMMR) method relies on the measurement of low-amplitude (similar to 100 pT), low-frequency (1-4 Hz) magnetic fields arising from galvanic current flow in the Earth. Normal magnetic sensors have been used extensively in surface magnetometric resistivity (MMR) surveys, but equivalent B-field probes have not been generally available for use in standard mineral exploration drillholes. However, recent advances in magnetic sensor design have led to the manufacture of B-field probes, which provide significant advantages over the alternative TEM probes for DHMMR surveys. Synthetic and laboratory examples highlight the differences between data acquired from B-field and TEM probes. Field examples from the Flying Doctor Prospect, near Broken Hill, New South Wales, demonstrate the improved resolution achieved by using a B-field probe for DHMMR surveys.