Simultaneous modelling of the phase and amplitude components of downhole magnetometric resistivity data

Abstract

The downhole magnetometric resistivity (DHMMR) technique is an effective method for follow-up exploration of massive and disseminated sulphide deposits. The method comprises the “in-hole” measurement of low-amplitude, low-frequency magnetic fields associated with galvanic current flow between two current electrodes. This paper presents methods for the simultaneous modelling of both the magnetometric resistivity (MMR) amplitude and phase (or magnetic-induced polarisation [MIP]) response for DHMMR data. Analyses of the MIP response and the interactions between conductive and polarisable bodies and their host are calculated using variations of the Cole–Cole model for complex impedance. The inphase and quadrature components provide symmetric signatures at the target depth, but some results are counter-intuitive when expressed as the MIP (phase) response. These methods are used to provide an interpretation of DHMMR data obtained from the Flying Doctor Prospect near Broken Hill, New South Wales.