Geologic applications of magnetic data and using enhancements for contact mapping

Magnetic field data are fundamental to geophysical approaches to geologic mapping. Both qualitative and quantitative methods are used to extract lithologic and structural information in the horizontal dimension while quantitative methods provide details in the third (depth) dimension. Recent research in magnetic methods continues to expand the capability of data measuring systems, efficiency of forward modeling algorithms, effectiveness of data transformations and the versatility of inversion approaches. Vector and gradient measurements are becoming more widespread, and consequently, interpretation methods must be geared to such expanded data sets. Forward algorithms are exploiting 3D frequency-domain representations and volume to line integral conversions to reduce calculation time. This is particularly timely because of the widespread use of 3D inversion codes. 3D inversion methods have also moved from simple unconstrained problems towards more constrained scenarios incorporating geologic, physical property and possibly other geophysical data. Recent years have also seen a rapid increase in the number of data enhancements that can be used to emphasize certain characteristics in the data resulting in a more easily interpreted representation. The question arises of whether they are all equally useful and effective. Here, we evaluate the utility of ten enhancements based on theoretical arguments, synthetic data modelling, and real data examples. One use of these transforms of particular interest for mapping in the horizontal dimension is locating lateral magnetization contrasts, which we equate with geologic contacts. We find that four of the methods considered are redundant, giving practically identical results for contact mapping. Two others produce similar levels of detail, so both are not needed. Data quality adversely affects two other enhancements, leading to poor continuity of the mapped contacts. The practical utility of each method depends on its performance in the presence of noise, non-vertical dips and non-vertical magnetizations.