The three-dimensional electrical characteristics of the typical iron and copper deposits in the Lujiang-Zongyang ore concentration area

The porphyrite iron and porphyry copper ore deposits are the major deposit categories in the Lujiang-Zongyang ore concentration area. However, previous researches were mostly focused on mineralogy, petrology, geochronology and geochemistry, but paid less attention to geophysics. As the exploration depth is increasing, geophysical methods become more important. In order to develop the interpretation 'scaleplate' of the geophysical exploration for typical deposits, the authors took the Nihe iron and Shaxi copper ore deposits as the research subjects, and obtained the three-dimensional electrical models of the orebodies and the surrounding rocks through the audio-magnetotelluric sounding. The results indicate that the major structure of the porphyrite (Nihe) iron deposit is composed of several layers including low resistivity sedimentary rocks, high resistivity volcanic rocks, relatively low resistivity alteration zone and relatively high resistivity intrusive of subvolcanic rocks from shallow place to the depth. In addition, the magnetite body, which exists as a dome on the top of the mass, presents the characteristics of high resistivity. For the porphyry (Shaxi) copper deposit, the major electrical characteristics are the massive (or longitudinal belt) structures composed of the shallow sedimentary rocks with low resistivity, the deep sedimentary rocks with relatively high resistivity, and the porphyry mass with high resistivity. In addition, the orebodies, which exist in the mass or the contact zone between the mass and surrounding rocks, present electrical characteristics of medium resistivity. The orebodies hosted in the mass (or in the contact zone with surrounding rocks) present medium-resistivity. For the practicability of the models, the authors converted the inversion results with complex electrical structures into two facilitate models, which would be used as the comparative 'scaleplate' for the discovery of the similar deposits.