Lithological Mapping by Correlating Magnetic and Gravity Gradient Airborne Measurements

Abstract

We report here two new applications of the Poisson relation useful when a joint magnetic and gravity gradient survey has been made. In the first, an apparent susceptibility contrast to density contrast ratio map (which we call the map) can be estimated. In the second, selected values of the above ratio are used in a filter to subtract from the magnetic field measurements the effect of a particular rock type. This would be especially useful as a filter of geological due perhaps to weathered magnetite products, particularly if the latter had an effect over a large area. As a test of these techniques we have applied them to a simulated joint airborne survey over a model which we designate Mini-Elura, in which the magnetic magnitude and vertical gravity gradient anomalies are not visible above the due to surficial variations. The computed pseudo-lithology map clearly distinguishes the regions of the map dominated by the alluvium source from those due to the Mini-Elura orebody, while the pseudo-magnetic filter does very effectively remove the noise due to the alluvium from the magnetic map.