Rectifying characteristics of semiconductor minerals: A model on seismo-electromagnetic radiation mechanism from ore bodies

Radiations of low to medium frequency (LF-MF) waves from ore deposits with semiconductor properties by rock burst have been reported. However, the radiation mechanism has not been fully understood yet due to the lack of knowledge of the semiconductor properties of ore minerals. So, we clarified the semiconductor properties of natural pyrite (FeS₂) by electroetching and indentation-type probe method. Due to the presence of impurities (particularly Pb), the pyrite possesses the quasi-diode junctions with rectifying properties. The current-applied voltage characteristic of the junctions can be represented by an equivalent circuit of the sample, and its forward breakdown voltage is estimated to be 0.3 V. Calculating the surface charge density and separation distance based on the contact electrification, the electric discharge could occur under Paschen's law during the process of contact or separating between ore deposits. Then, the electromagnetic radiation from ore deposits depends on dielectric characteristics, and the skin depth of pyrite for LF-MF waves is estimated to be in the range of 0.1–1 m, indicating the radiation only from the surface deposit excited by seismic wave. Furthermore, the current-voltage characteristics of semiconductor minerals can be changed by the variation of the capacitance and the parallel resistance of the equivalent circuit of semiconductor minerals associated with contact pressure changes. With respect to the dielectric characteristics of ore deposits, the resistivity presents the diameter of circular arc on the complex-plane impedance diagram. Therefore, the continuous monitoring of complex resistivity, such as induced-polarization (IP) method, would detect electromagnetic phenomena associated with earthquakes in dry ore deposits.