Current channeling in borehole EM methods for weak conductors

Abstract

Summary This paper presents some results from a 3-year research project targeted towards processing and interpretation methodologies for borehole EM methods in the search for weak electrical conductors This paper summarises five of the results of the project: x Recognition of the importance of using currentchanneling energisation of weak conductors. A sphalerite-rich or gold-bearing disseminated sulfide conductor is frequently too poor a conductor to support an inductive EM response of vortex currents, but any conductor showing a conductivity contrast relative to host rock, can produce an EM response from currents channeled through the conductor from the conducting host rock. x Recognition of the equivalence of MMR and longoffset TEM data, in terms of information and interpretation of current-channeling energisation of conductors. x Comparison of numerical modeling techniques for inductive and current-channeling responses in TEM surveys using state-of-art 3DEM modeling software (MARCO and LEROI); identification of instabilities in multiple-plate modeling in LEROI . x Development of a fast approximation algorithm for modeling the three-component MMR or currentchanneling EM response of multiple 3D conductors. x Recognition of the importance of correct modeling of the MMR response of a layered earth as a precursor to stripping background and modeling of residual MMR anomalies.