The IP phase measurement and inductive coupling

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.