大地电磁法在重庆秀山成锰槽盆深部结构调查中的应用

Application of magnetotelluric method in investigation of deep structure of Xiushan manganese basin in Chongqing

黔湘渝毗邻区的“大塘坡式”锰矿床,是南华裂谷盆地形成过程中的次级拉张、断陷小盆地中的沉积产物,查明成锰槽盆的深部结构与主要控盆断裂的空间形态,能够为锰矿资源的远景评价及勘探开发提供深部构造证据。以重庆秀山小茶园锰矿床毗邻区的楠木庄预测成锰槽盆为勘探对象,垂直构造走向布置完成一条宽频带大地电磁勘探剖面,结合研究区的地质构造背景开展了地质地球物理综合解释,解释结果显示:①茶园锰矿床发育于鸡公岭背斜构造,该背斜构造深部电性结构横向与纵向不均匀性特征明显,该背斜构造的边界断裂为楠木庄断裂和漆园坝断裂,断裂带表现为明显的电性梯级带;②楠木庄预测成锰槽盆位于次级獠牙盖地堑盆地中,槽盆深部总体表现为高阻-低阻-高阻的三层电性结构特征,中间低阻层最深处可达地下6 km;③综合分析楠木庄预测成锰槽盆深部电性结构与中间低阻层的埋深,认为该槽盆内发育锰矿床的前景较大,但由于埋深过大,开采价值有限。

The"Datangpo"manganese deposit in the adjacent area of Guizhou,Nunan and Chongqing is the sedimentary product of secondary tension and small faulted basin in the formation process of nanhua rift basin.To find out the deep structure of the manganese basin and the spatial morphology of the major basin-controlling faults can provide deep structural evidence for the prospective evaluation and exploration and development of manganese resources as well.This paper takes Nanmuzhuang predicted manganese tank,adjacent area of Xiushan Xiaochayuan manganese deposit in Chongqing as the exploration object.A wide band magnetotelluric exploration section was completed in vertical structure strike arrangement,combined with the geological and tectonic background of the study area.The comprehensive interpretation of geology and geophysics is carried out.The interpretation results show that:(1)The Xiaocayuan manganese deposit is developed in the Jigongling anticlinal structure.The deep electrical structure of the anticlinal structure has obvious characteristics of transverse and longitudinal heterogeneity.The boundary faults of the anticlinal structure are Nanmuzhuang fault and Qiyuanba fault.The fault zone shows obvious electrical stepped zone.(2)Nanmuzhuang predicated manganese trough basin is located in the secondary Liaoyagai basin.The deep part of the trough basin was generally characterized by the three-layer electrical structure of high-to-low resistivity,and in the middle,low resistivity layer was as deep as 6 kilometers underground.(3)Based on the analysis of the deep electric structure and the buried depth of the middle low-resistivity layer of the Nanmuzhuang forecast manganese trough basin,it is believed that there is a great prospect for the development of manganese deposit in the trough basin,but due to the excessive buried depth,the mining value is limited.