Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Figure 7. Plan slices through 3D gravity and magnetic inversion results for the 2007 QUEST data.
Each model is contained within a mesh with 780 by 924 by 44 cells in the east-west, north-south,
and vertical directions respectively. Grid lines mark out 100 km squares.
Class analysis of gravity and magnetic inversion results
Additional processing, analysis, and interpretation work has been commissioned by Geoscience BC to
familiarize the exploration community with the use of the new gravity, magnetic and electromagnetic
inversion methods and thereby add value to the new and existing regional data.
A useful additional process that can be applied when inversion of gravity, magnetic and
electromagnetic data have been carried out is to construct response classes from the density,
susceptibility and conductivity inversion models. As different lithologies can often have distinct ranges
of density, susceptibility and conductivity properties, separating the models into groups of cells with
similar properties will produce a map that is a proxy for geology. The use of a 3D inversion results
extends this map into 3D.
Figure 8 shows a simple classification of the inversion results based on a classification of density and
susceptibility properties. The classification was done manually by examination of the cross-plot of the
density 3D mesh property values against the susceptibility 3D mesh property values (Figure 8a). In
this example, there were 19 classes generated. Each class was assigned a separate colour and then
mapped onto the 3D model mesh. Figure 8b shows a plan slice through the class model. This has a
highly geologic appearance, and is of immediate aid for mapping of geology under cover.
The method can be extended to include other physical properties. In the QUEST area the basement
conductivity inferred from the inversion of the regional can be added to produce a classification based
on three physical properties – density, susceptibility, and conductivity.
The maps produced are of immediate aid to geologists and prospectors in the field. They provide
additional information not intuitively understood when looking at the data alone.
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