Identifying the nature of lithogeochemical boundaries in drill holes

Abstract

There is a need for rapid and reliable techniques for extracting geological information from geochemical data derived from exploration drill hole samples because geochemical data bases are becoming too large to interpret manually. Automated boundary detection techniques which use the continuous wavelet transform are a popular method for extracting multi-scale geological boundaries from drill hole signals. However, these boundary detection techniques do not distinguish between sharp and gradational boundaries, which may be an important factor when interpreting the geology of the subsurface or calculating resource estimates. This paper demonstrates how a scale-dependant measure of relative sharpness of the boundary can be extracted from the results of the continuous wavelet transform. The results of the automated method are compared against the interpretations of 15 geologists. The comparison demonstrates the need for alternative boundary selection methods when boundaries are not sharp. The results also demonstrate how the multi-scale nature of the sharpness measure allows for reliable gradient analysis in noisy signals.