Lithological mapping by correlation of the magnetic and gravity data from Corsair W.A.

Abstract

The pseudo-lithology mapping technique developed by Dransfield et al. (1994) for use with coincident gravity gradient and magnetic measurements and demonstrated with synthetic data is applied here to measured field data. Application of the pseudo-lithology method utilised total magnetic intensity data (TMI) and gravimeter measurements, whereas Dransfield et al. (1994) required gravity gradient information which is not yet practically available. The 'pseudo-magnetic projection' of the gravity gradient is developed from Poisson's relation and then correlated with the magnetic data, resulting in a 'pseudo-lithology' map of the ratio of apparent susceptibility to density contrast. One of the main advantages in using this correlation is that the information contained is independent of source geometry and depth. The technique was applied to data from the Corsair locality in Western Australia (Price, 1993), proving very useful in the determination of the subsurface geology, and extending the interpretation of previous workers (Whitaker et al., 1987). We also provide an error estimate of the derived horizontal and vertical gravity gradients, exploiting the zero trace of the gradient tensor. This furnishes us with a noise estimate of the gravity data, and also an edge detector for continuous rock units. This edge detecting ability is also apparent in the pseudo-lithology maps, aiding the interpretation.