In‐situ complex resistivity measurements over the frequency range [Formula: see text] to [Formula: see text] have been made on 26 North American massive sulfide, graphite, magnetite, pyrrhotite, and porphyry copper deposits. The results reveal significant differences between the spectral responses of massive sulfides and graphite and present encouragement for their differentiation in the field. There are also differences between the spectra of magnetite and nickeliferrous pyrrhotite mineralization, which may prove useful in attempting to distinguish between these two common IP sources in nickel sulfide exploration. Lastly, there are differences in the spectra typically arising from the economic mineralization and the barren pyrite halo in porphyry copper systems. It appears that all these differences arise mainly from mineral texture, since laboratory studies of different specific mineral‐electrolyte interfaces show relatively small variations. All of the in‐situ spectra may be described by one or two simple Cole‐Cole relaxation models. Since the frequency dependence of these models is typically only about 0.25, and the frequency dependence of inductive electromagnetic coupling is near 1.0, it is possible to recognize and to remove automatically the effects of inductive coupling from IP spectra. The spectral response of small deposits or of deeply buried deposits varies from that of the homogeneous earth response, but these variations may be readily determined from the same “dilution factor” [Formula: see text] currently used to calculate apparent IP effects.

Recent work by Van Voorhis et al (1973), Zonge et al (1972), Pelton (1973), and others has begun to make available some information concerning the phase shifts that accompany the IP effects used in mineral exploration. A portable system is now available to measure phase shifts in the field in the frequency range from 0.05 hz to 1.25 hz with an accuracy of a few milliradians. Field work with this system confirms that the phase shift associated with the IP effect from metallic mineralization is relatively constant at all frequencies within this frequency range. The inductive coupling effects (for the dipole‐dipole electrode configuration) give phase shifts that increase approximately linearly with frequency for a uniform or layered earth. Theoretical solutions and scale modeling suggest that this is also a valid approximation for two‐dimensional resistivity variations of considerable extent. Therefore, it should be possible to use accurate phase measurements, at several closely spaced frequencies, to separate IP effects from inductive coupling effects.

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The increased use of the induced‐polarization method in recent years has resulted in two methods of measurement. The measurements in the frequency domain (variable‐frequency method) rely on changes in the apparent resistivities measured as the frequency of the applied current is varied. The measurement in the time domain (pulse‐transient method) detects transients in the measured potentials when the applied current is interrupted. The “chargeability” is the parameter used in the pulse‐transient method, while both the “frequency effect” and the normalized parameter “metal factor” are used in the variable‐frequency method. The most useful parameter would be the one which best indicates the amount of metallic mineralization present. Eight sets of field results from variable‐frequency field surveys are shown. The cases are shown in pairs; in each pair, the geometry of the source is much the same. By comparing the resistivity, the frequency effect (chargeability), and metal‐factor data with the amount of mineralization indicated by the drilling results, the usefulness of these parameters can be evaluated.