Scale-dependent electrical properties of sulphide rocks ? new methods and techniques

Abstract

A thorough understanding of the the influence of geological factors on electrical petrophysical properties of sulphide orebodies requires careful integration of geophysical and geological measurements at a variety of scales. Two new methods for studying the influence of microscopic and mesoscopic ore textures on electrical properties of sulphide rocks have been developed. Voltage contrast microscopy is a scanning electron microscope technique which enables direct imaging of the effects of an applied potential on a polished rock surface. It has been used to investigate the detailed mechanism of electrical conduction in fine-grained base metal sulphide ores. Initial results suggest that conductive paths may exist along grain boundaries within otherwise resistive minerals, such as sphalerite. Continuity mapping uses a modified flat-bed plotter to directly image the electrical continuity of drill core or hand specimens. A spring-loaded copper electrode traverses the polished sample surface on a grid to produce an image. Electrode movement and potential measurement are fully automated. This technique has been used to study the influence of mesoscopic ore textures on the electrical continuity of massive and disseminated sulphide ore samples. Both new methods are still being developed and refined but initial results suggest that they will usefully complement existing laboratory-based petrophysical techniques