Airborne geophysics in Western Australia

Abstract

Aeromagnetics became recognised as a valuable aid to exploration in Western Australia during the 'nickel boom' of the 1960s. The now commonplace term 'high-resolution aeromagnetics" evolved during the 1980s, mainly to meet demands of a resurgent gold exploration industry which required a greater understanding of geological structure and rock type than was possible with conventional field mapping. High-resolution aeromagnetic surveys are typically flown at a line spacing of 200 m, a terrain clearance of 60 m and with a magnetometer sampling interval of 7 m. Imaging of the data provides a greater range of options for highlighting subtle structural features than conventional contours. Image maps may be interpreted using skills of photogeology and satellite-image interpretation and have been a major factor in bridging the communication gap between geophysicists and geologists. The effectiveness of radiometric data in Western Australia, collected simultaneously on virtually all high-resolution aeromagnetic surveys, has been constrained by lack of outcrop and transported soils. In appropriate areas the method is successful at mapping different types of felsic igneous, sedimentary and metasedimentary rocks, and also in identifying hydrothermal alteration zones displaying potassic enrichment. Problems of high surface conductivity have, in the past, limited the application of airborne time-domain electromagnetic surveys. The new generation of digital systems (e.g., QUESTEM) has improved depths of penetration through the real-time removal of unwanted noise. Airborne time-domain electromagnetics is no longer only an anomaly detector, but a three-dimensional regional conductivity mapping tool which, when integrated with magnetic data, enables the targeting of bedrock conductors to be controlled by interpreted geology.