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
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摘要:
近年来，山东齐河—禹城李屯厚覆盖区富铁矿勘查取得了重大进展，但该区新生界厚度大(900~1100 m)、磁铁矿体埋藏深，矿体引起的地球物理异常弱，找矿难度大。为了揭示李屯富铁矿深部地质构造，开展了分布式三维广域电磁探测，应用高阶2n序列伪随机信号，一次发射49个频率并同时接收，实现分布式滚动测量，获得了地下2000 m以浅地电特征，并对地下地质结构进行解释，构建了重点研究区的三维地质模型，解释结果与已有的二维地震和钻探信息吻合度较高，为重磁联合反演提供有效的地质结构约束，结合重磁场特征和成矿规律圈定新的找矿靶区。结果表明，分布式三维广域电磁法是获取厚覆盖地区深部地质结构的有效探测方法，具有良好的应用前景。
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关键词:
- 分布式三维广域电磁法 /
- 富铁矿 /
- 厚覆盖区 /
- 山东
Abstract: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.
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图 3 高阶2n序列伪随机信号（Yang et al.，2022）
Figure 3.
表 1 地层电阻率测井参数
Table 1. Statistics of formation resistivity logging parameters
地层 归一化电阻率/（Ω·m） 统计厚度/m 极值 平均值 Q 13~15 13 2980 N 6~14 8 4015 C+P 40~178 78 2146 矿体 2~18 9 256 角岩 59~194 160 325 蚀变闪长岩 34~138 67 475 闪长岩 1351~1656 1619 573 注：Q—第四系；N—新近系；C+P—石炭系−二叠系 
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