Medidas de Condutividade Elétrica Complexa de Amostras de Rochas da Área MM1-Alvo 1 - Distrito dos Carajás

Abstract

Laboratory measurements of complex conductivity were made on 28 drill core samples from area MMI-Prospect 1 of the Carajás Mining District. The-objective of this Research was to help the interpretation of field geophysical survey of the area using induced Polarization and AFMAG methods. The laboratory measurements of amplitude and phase of conductance were taken in the frequency interval of 10-3 Hz to 104 Hz. The method used was the direct measurement of impedance using a memory oscilloscope, a signal generator, and two high input impedance differential preamplifiers. A petrographic study of the samples was carried out using thin sections, polished sections and X-ray diffraction. Copper contents in the form of sulphides was determined using atomic absorption. As a result of the petrographic study, the samples were classified in five distinct groups: granite, biotite schist, amphibolite, amphibole schist and magnetite quartzite-iron formation. In the conductivity measurements ¡t was observed that, among the five groups, the samples of iron formation gave the largest frequency variations. The granite samples had spectra flatter than those of schist or amphibole' ln conclusion, these measurements show that the field induced Polarization and AFMAG anomalies near these three drill holes (F1, F2 and F3) are due primarily to the magnetic iron formation, and secondarily due 1o associated low-grade chalcopyrite mineralization.