A Sub-Audio Magnetics case study: Flying Doctor Pb-Zn-Ag Deposit, Broken Hill, Australia

Abstract

The Flying Doctor Deposit is located approximately 5 km north-east of Broken Hill, NSW. The area lies along strike from the main Broken Hill ore bodies and is considered highly prospective for the development of base-metal sulphide mineralisation. The deposit was originally detected by induced polarization profiling techniques. Subsequent drilling in 1965 led to the discovery of a massive sulphide body. Over the last 20 years, comprehensive geological and geophysical data have been acquired at the site and consequently, the Flying Doctor Deposit has become an important test site for the evaluation of new geophysical techniques in the Broken Hill region. One of the first Sub-Audio Magnetics (SAM) trials was conducted at the Flying Doctor deposit in late 1992 to test the feasibility of acquiring total field magnetometric resistivity (TFMMR) data simultaneously with high definition total magnetic intensity (TMI) data. Subsequent trials in 1995 focussed on acquiring total field magnetometric induced polarization (TFMMIP) and total field electromagnetic (TFEM) parameters. It was found that the Flying Doctor Deposit exhibited no magnetic susceptibility contrast but that the mineralisation was readily detected by both the TFMMR and TFMMIP parameters. This paper describes the results of the TFMMR/TFMMIP surveys and compares them with results obtained with prior surveys including gradient-array induced polarization (IP), dipole-dipole array induced polarization and magnetic induced polarization (MIP) surveys. The SAM trials demonstrated that it is possible to map several geophysical properties simultaneously with a single instrument, and confirmed that SAM is capable of acquiring data cost-effectively at spatial resolutions equivalent to high definition magnetics. An important conclusion from the surveys was that much greater interpretative power can be derived from having multiple data sets which reflect independent physical properties.