Abstract
Complex resistivity spectra, in the frequency range 0.001 to 10 hz, have been obtained through computer analysis of waveforms tape recorded at porphyry copper deposits. When care is taken to avoid distortions caused by the geometric effects of electrical inhomogeneities, the spectra of typical porphyry copper mineralization are remarkably uniform in character. The geometric effects of veins, which generally complicate the response of hand samples, can be reduced through in-situ measurements using electrode separations of a few meters.In the frequency range of interest for induced-polarization (IP) exploration, the observed spectra are accurately described byEquationwhere K is a constant and b is a positive fraction.The fraction b has a value less than 0.1 and is a complete measure of IP. In the frequency range of interest, Laplace transformation gives the step response to be approximated byEquationTypical current waveforms used in IP prospecting can be synthesized by superposition of steps. Using these frequency and time response functions, percent frequency effect, phase, and pulse-transient parameters are compared as measures of IP.By using a volume distribution function, it is shown that a distribution of lossy capacitors will explain the observed response. Physically, this might correspond to the double-layer capacitance of metallic particles in mineralized rock.
