Source Component Display and Potential Field Interpretation

2D or 3D gravity and magnetic modelling procedures usually involve comparison of the response from a few, or simple, sources with an observed profile. Common software may also allow complex source distributions typical of a complete geological section.

When several sources are involved the observed profile may be the result of complex interference and individual contributions may not be obvious. Gradients may be transformed by such interference. Much trial and error may be required to resolve or understand the source and effect interactions. This is not a simple process if only the resultant calculated from all sources is compared with the reference profile.

A source component profile represents the response due to a specific source within a model.

Assessment of critical geometry or contrast changes, crucial source segments and curve fitting parameters - and hence model revision, can be greatly accelerated if the actual responses from each part of the model are viewed in addition to the resultant of their effects. Review of the source contributions in a model leads to more satisfactory interpretations since it reveals how the observed profile may, or may not, be composed. Component profiles also demonstrate how observed and resultant gradients may be modified by interference and thus provide some salutory cautions about the use and reliability of simple procedures. Software should be modified to allow this more complex display and a declaration of how the resultant and observed curves were fitted. Most currently available modelling software either generates, stores or requests the required information.

The paper includes examples from the Mount Isa Inlier of NW Queensland to illustrate the use of source components.