Wemeasured Spectral Induced Polarization responses of 22models of disseminated orewith a time domain (TD) technique. Themodels weremixtures 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%. Weobtained IP decays with a conventional field TDmeasuring technique and a lab low-current transmitter in the time range from0.3 ms to 64 s. The IP decaysmeasuredwith various currentwavelength 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