Application of distributed 3D wide field electromagnetic method in the exploration of high-grade iron ore in the thick covered area of Litun in Qihe−Yucheng, Shandong Province

In recent years, significant progress has been made in the exploration of high-grade iron ores in the Litun heavy-cover area of Qihe—Yucheng, Shandong Province. But the Cenozoic thickness (900~1100 m) in this area is so large that the magnetic iron ore is deeply buried. The geophysical condition caused by the iron ore is thus abnormally weak, and the prospecting is difficult. To reveal the deep geological structure of high-grade iron ore in the Litun, distributed three-dimensional wide field electromagnetic detection was carried out. The high-order 2ⁿ sequence pseudo-random signal was used, which can transmit 49 frequencies at a time and receive at the same time, realize distributed rolling measurement, and obtain the geoelectric characteristics of 2000 m underground. Based on this, a detailed interpretation of the underground geological structure was carried out, and a three-dimensional geological model of the key research area was constructed. The interpretation results were in good agreement with the existing seismic and drilling information. It provides effective geological structure constraints for gravity-magnetic joint inversion. Delineates new prospecting targets in combination with gravity and magnetic characteristics and metallogenic laws. The results show that the distributed three-dimensional wide field electromagnetic method is an effective detection method to obtain the deep geological structure in the heavy-cover area and has a good application prospect.