Abstract

The induced polarization and resistivity of a suite of 74 synthetic, low porosity, 'rock' specimens were measured by the pulse transient method. The specimens contained up to 8 percent by volume of sulfide particles in three different grain sizes. A measuring cycle of 5 sec on and 5 sec off was employed, and discharge potentials were recorded for 4 sec by oscilloscope photography. Charging current density was varied between 125 mu a/cm 2 and 0.0125 mu a/cm 2 .Chargeability--defined as the time integral, from 15 to 415 ms after cessation of charging, of the instantaneous discharge potential divided by the charging potential--was found to vary from 1 to 30 ms. For current density less than about 0.1 mu a/cm 2 , it was independent of charge current density, but decreased about 20 percent/decade with increase in current density. A background chargeability of a few milliseconds, virtually indistinguishable from the sulfide IP, was found in nonmineralized specimens and assumed to be present in all. Chargeability due to metallic minerals was found to be proportional to sulfide content (volume percent) and to decrease with increasing grain diameter, as predicted by the theory developed by Wait. The observed decay forms were not exponential as this theory predicts, but were approximately logarithmic. The metallic mineral-electrolyte interface impedance determined for the specimens by use of Wait's theory is consistent with that measured directly by Anderson and Keller for a clean pyrite interface.

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