The Use of Gravity and Magnetic Surveys in Mapping Greenstone Terrane Near Kalgoorlie, Western Australia

Abstract

This paper compares the usefulness of several types of detailed airborne and ground magnetic surveys, and a detailed gravity survey, in mapping the geology of the Corsair area, about 10 km east of Kalgoorlie. The gravity and magnetic surveys when interpreted together map out the distribution of mafics, ultramafics and sediments. The mafic rocks are only weakly magnetic, but they generate an easily observable gravity anomaly of about 20 µm.s-2. Surficial deposits are associated with both elongate and high-amplitude short-wavelength magnetic anomalies; their distribution can best be mapped as the area of short-wavelength anomalies in the unsmoothed observations (dappled on pixel maps). The magnetic field due to basement is best derived by attenuating the high-amplitude short-wavelength anomalies; this is most reliably done by estimating the mode, rather than the mean, of the observations. The airborne gradiometer survey gave superior results to both the aeromagnetic total intensity survey, and the ground magnetic survey, in that it contained the short wavelength information required to map the surficial deposits, and it had better detail of the anomalies due to the basement. The image of the gravity gradient provided the best representation of linears. Many of these linears are in part coincident with workings, so they are gold carriers. Known gold mineralization is preferentially developed along a sheared zone abuting the boundary between the two major basement rock associations; this zone corresponds with the major gravity gradient.