Gravity and magnetic tensor data: Possible use in regolith exploration

Abstract

The regolith obscures much of Australia's bedrock geology, posing problems in mineral exploration under cover. Gravity and magnetic tensor data may provide significant improvements over conventional geophysical exploration, by producing maps showing subtle variations in the field data which relate to the subsurface geology, but hidden to standard total or vertical field measurements. This paper examines forward potential field responses of three-dimensional regolith models containing targets like palaeochannels and land mines. A finite element approach is used, summing the field responses from many small elementary cubes, to build up complex structures to yield the full field response at a specified height above the ground. The gravity tensor data ranges over values from ?0.08 to 0.1 Eotvos, and magnetic data range from ?40 to 40 nanoTeslas per metre (when measured at the surface). When a flight height of 80 m is used, the responses diminish significantly, and only regional features are detectable. These values are compared to the ranges of measurable values from existing systems, and it is shown that the magnetic case is most suited to regolith studies. The resolution required for the gravity tensor appears to be less than is possible with current systems.