Time domain spectral induced polarization of disseminated electronic conductors: Laboratory data analysis through the Debye decomposition approach

• Total chargeability is a direct measure of the metallic particle content.
• Total chargeability is independent of the ore grain size.
• Relaxation time increases with increase of the ore grain radius.
• Ore grain relaxation is much faster than that of silica grain with the same radius.

We measured Spectral Induced Polarization responses of 22 models of disseminated ore with a time domain (TD) technique. The models were mixtures of calibrated sand (0.2–0.3 mm) with calibrated ore grains (average radii: 0.045, 0.055, 0.13, 0.20, 0.38 and 0.55 mm). The grains represent a mixture of pyrrhotite (30%), pyrite (30%), magnetite (30%) and chalcopyrite (10%) coming from a natural ore. In the models, the grain concentration (by volume) varied between 0.6 and 30%.We obtained IP decays with a conventional field TD measuring technique and a lab low-current transmitter in the time range from 0.3 ms to 64 s. The IP decays measured with various current wavelength forms were inverted to relaxation time distributions (RTD) on the basis of the Debye decomposition approach.RTD parameters were found to be closely related to the ore volumetric content and the ore grain size. The total chargeability is independent of the grain size, but is determined by the grain volume fraction. In contrast, the mean IP relaxation time is related to the grain size. These facts make RTD attractive to use in ore prospecting and studying reactive permeable barriers.Moreover, for low salinity pore water used in this study, the relaxation times of disseminated ores are three to four decades smaller than that of the insulating grains of the same size typical of common soils and sediments. This allows recover the relaxation times on the basis of relatively fast IP measurements with short time pulses (in TD) or high frequency values in the frequency domain; however attention should be paid to inductive and capacitive couplings.