音频大地电磁法在深部隐伏锰矿找矿中的应用——以贵州松桃普觉锰矿为例

Application of audio magnetotelluric method in prospecting for deep hidden manganese ore: A case study in the Pujue manganese mine in Songtao,Guizhou,China

普觉锰矿是黔东地区典型的南华纪"大塘坡式"沉积型锰矿床。区内一系列后期构造对早期形成的沉积型锰矿的埋藏和保存具有重要影响,深部构造格架及其与含锰岩系之间关系的勘查分析对区内找矿预测和深部锰矿勘查十分关键。为了查明普觉锰矿区成矿地质体和断裂构造的空间分布及其相互关系,采用音频大地电磁法(简称AMT)对区内地下电性结构特征和构造格架进行研究。在物性分析的基础上,构建了与测区地电结构大致相似的构造理论模型,通过开展不同模式的理论模型反演计算,优选出了适宜于研究区的Occam-TE一维反演为初始模型的非线性共轭梯度TM模式二维反演方法。运用上述反演方法对区内实测数据进行反演,识别了区内构造格架和含锰岩系的空间展布特征及二者的接触关系,查明了断层F;在深部未对含锰岩系造成破坏。应用研究结果表明,AMT对指导普觉锰矿区及毗邻地区开展深部找矿预测意义重大。

The Pujue manganese deposit is a typical Datangpo-type sedimentary deposit of Nanhua period in eastern Guizhou. In the Pujue mining area the early-formed sedimentary manganese deposits were significantly influenced by the subsequent structures in aspects of burial and preservation. Analyzing the deep tectonic framework and its relationship with the manganese-bearing rock series is of great importance to the ore-prospecting prediction and deep exploration of the manganese deposits in the area as well. Our aim is to find out the spatial distribution of metallogenic geological bodies and fault structures and their relationship in the Pujue Manganese mining area. We used audio magnetotelluric method to study the characteristics of underground electrical structure and tectonic framework in the area, and built a theoretical model similar to the geoelectric structure of the study area based on the physical property analysis. Through inversion calculation under different schemas, we gave preference to a two-dimensional inversion method of nonlinear conjugate gradient TM model, which is suitable for Occam-TE one-dimensional inversion as the initial model. We used the above inversion method to invert the measured data from the area, and thus identified the spatial distribution characteristics between the tectonic framework and the manganese-bearing rock series and their contact relationship. It demonstrates that the fault F;hasn’t damaged the manganese-bearing rock series in the deep. Our research results show that AMT is of great significance in guiding the deep prospecting prediction in the Pujue manganese mining area and its adjacent areas.