1978 Volume 28 Issue 149 Pages 163-175
Many previous articles about the theories and experiments related to induced polarization phenomena indicate that the I.P. is quite a complicated matter affected by various physical and chemical factors of sulfide minerals and groundwater at the contact. It was rather difficult to understand completely the I.P. phenomena at the Kuroko ore field only from these references. The investigation of I.P. characteristics for specimens of sulfide ores and country rocks with sulfide mineralization from Kuroko ore fields have been carried out. The relation between laboratory results and field I.P. response has been discussed quantitatively.
We started the experiments from observation of interface impedance for several combinations of ore types and varieties of solution. Then tank model experiments, theoretical analyses of the results and I.P. logging tests at the field have been followed up. The interface impedance observed about conductive massive sulfide ore samples shows a narrow range of "characteristic value (W)" of Warburg impedance, which is around 5 kilio-ohm-cm 2 /√sec. Neither the variation of sulfide minerals nor the, concentration of relevant ions in the solution seems to affect practically the magnitude of I.P. response of an ore body. The mathematical expression (3) was introduced for the peak value of I.P. anomaly of a spherical massive ore body model placed in a uniform current field of pulse type, and its validity was proved by the tank model experiments.
It was observed that the total impedance of massive sulfide specimen increased when the amount of internal interfaces was increased artificially. The state of ore body with many internal interfaces is supposed to be common in nature and it will be called "mosaic massive". A single massive ore body would exist only ideally. While the expression (3) with (4) implies that a large scale single ore body requires long current pulse width more than hundreds seconds for a sufficient I.P. response, the mosaic massive is expected to respond well to the pulse width of less than ten seconds on account of increased impedance. A difinite I.P. response of massive and compact pyritic ore body in a part of the Etsuri deposits was observed by I.P. logging using conventional type of I.P. equipment and large electrodes spacings.
Analysis of decay voltage curves for specimens of both veined rock and massive black ore with abundant insulating minerals (e.g. barite rich black ore) gave the same range of the "I.P. decay factor (α)" as the mosaic massive. Impregnation of small particles (less than 1 mm) of sulfide minerals in country rocks is anticipated from the expression (5) to give little effect on the results of I.P. survey at the Kuroko field. The mineralized dacite body underneath massive sulfide ore body at Etsuri showed high I.P. effect on I.P. log measured with 2 sec. of pulse width. This is interpreted as the result of veined rock effect rather than that of impregnation. An I.P. anomalous body of extensive size has revealed by the compilation of I.P. logging results for 21 drillholes around Etsuri ore deposits.
