Electrical Properties of Magnetite- and Hematite-Rich Rocks and Ores

Abstract

Magnetite and hematite are common iron-oxides, being found in sedimentary, metamorphic and igneous environments and being associated with a wide variety of deposits styles, including orogenic gold, iron-oxide copper-gold and iron-ore deposits. While the magnetic and mass properties of magnetite and hematite have been comprehensively studied, there is relatively limited published information on their electrical properties, although anecdotally, it would appear that many geophysicists have encountered the situation in which their ?highly prospective? EM or IP anomaly has turned out to be the result of barren magnetite, and/or hematite. In 1994, Emerson and Yang extensively studied the electrical properties of magnetite-rich rocks as part of AMIRA project P416. Eight sponsor companies contributed a variety of samples for laboratory measurements of mass, magnetic, galvanic electrical, electromagnetic and induced polarisation properties. A petrological study was also carried out. The electrical properties of hematite have been similarly investigated on behalf of individual companies. This work has demonstrated that sulphide-free, magnetite- and/or hematite-rich rocks can be moderate to good conductors and also exhibit a measurable IP response. And in some cases, electrical anisotropy may be significant. The electrical behaviour of magnetite and hematite is related to factors such as quantity, grain size and texture and their electrical response can be considerably enhanced by relatively small amounts of sulphides, such as chalcopyrite. Field examples are presented confirming laboratory observations.