Three-dimensional electrical structures and significance for mineral exploration in the Jiujiang-Ruichang District

The Jiujiang-Ruichang district is one of the most important Cu-Au ore deposits in the Middle-Lower Yangtze metallogenic belt of eastern China, as well as one of the integrated exploration zones in China. In the past geological exploration has found shallow subsurface metallic ore deposits, and the prospecting for deep deposits is the present emphasis in this region. The objective of this work was to detect the three-dimensional electrical structures from AMT surveys, which provide information for prospecting of deep deposits in the Jiujiang-Ruichang district Firstly, we examined the characteristics of the regional geology, tectonics and magmatic rock. We conducted statistical analyses of the stratigraphic and lithologic resistivities with measurements of 1125 rock samples. Secondly, we collected audio magnetotelluric (AMT) data over a 23 kmx20 km area in the Jiujiang-Ruichang district, which included 23 profiles oriented NS, each 20 km in length and 1 km in width using frequencies ranging from 0.35 Hz to 10400 Hz. We implemented two-dimensional (2D) non-linear conjugate gradient (NLCG) inversion with TM mode data using a Lagrange multiplier of 3 for the whole Jiu-Rui metallogenic district. Finally, by integration and 3D gridding of the 2D inverted resistivity data, we established 3D electrical structures for the total of the 23 AMT profiles. The results show the formation distribution, the regional structures, and the 3D undulating basement as well as the location of magmatic vents. After comparing the results with the known deposits at the Jiu-Rui metallogenic district,we found that the prospective areas of mineralization are located in the places where shallow NW faults and deep NE faults cross, the groove edges of the basement are uplifted, in addition to the margins of magmatic rocks.