推覆构造控矿的地球物理响应研究

Detection of the buried ore in deep subsurface with geophysical methods faces various difficulties. To deal with various problems, we conducted some fundamental researches about the technique of the depth migration imaging starting from the true surface. In our research, the shallow near surface information was retained, and the full depth domain velocity model was constructed as well. The shallow velocity structure and the distribution of the datum depth were determined by comprehensive use of statics correction, time migration and the lateral inhomogeneous inversion of gravity, magnetic and electrical data. The deep velocity structure was determined by velocity analysis, time-depth conversion and factor correction. Then, the upper-mentioned velocity structures were merged together, and the waveform inversion was utilized to correct the velocity structure. In this way, the full depth domain velocity model can be constructed. At this point, the true surface prestack reverse-time migration was implemented to image the subsurface structure under the condition of complex surface and structures, and made it possible that break through take place in the seismic exploration technology in metal mines areas..With techniques mentioned above, we conducted research of the geophysical reaction of polymetallic ore deposit controlled by nappe structure in Dapai lead-zinc polymetallic mine area in the southwestern Fujian province. The datum that utilized include the data from high resolution reflection seismic, the data from electromagnetic method, the large scale gravity and magnetic data by collection, geochemical data and drilling data. Based on seismic migration imaging and inversion results of electromagnetic, gravity and magnetic data, we constructed the geological interpretation model of some main profiles in Dapai mining area and the three dimensional initial model of this area. Based on former research, we will also summarize the metallogenic regularities, mineralization and control factors in Dapai polymetallic mine area. The establishment of the model of mineralization and prospecting in deep subsurface as well as the flag of prospecting is another task. Furthermore, we will carry out deep metallogenic prediction in this area to provide theoretical and technical support for the prospecting of polymetallic mines in the southwestern China.

针对深部隐伏矿勘探中的难题，开展保留近地表信息，构建全深度域速度模型，进行从真地表开始的深度偏移成像的方法研究。通过静校正、时间偏移和重磁电横向不均匀反演相结合确定浅层速度结构和基准面深度分布；通过速度分析、时深转换和因子校正确定深层速度结构；二者合并后进一步通过波形反演修正获得精确的全深度域速度模型，利用真地表叠前逆时偏移，实现金属矿区复杂地表与构造条件下的地下结构构造精确成像，使深部隐伏矿探测方法取得进展。在闽西南永定大排多金属矿区，实施反射地震、电磁法勘探、以及收集大比例尺重磁资料、化探资料和钻井资料等，在地震偏移成像和重磁电反演的基础上，构建矿区骨干剖面的地质解释模型和矿区三维初始模型，总结推覆构造控矿的地球物理响应特征，总结矿区的成矿规律、成矿作用和控矿因素，建立找矿模式和找矿标志，开展深部成矿预测。为深入认识中国南方主要成矿带的成矿特征和指导深部找矿提供理论和技术支撑。

闽西南大排矿区是福建省较大的多金属矿产地。前人根据对已知矿床的深入研究，提出了“赋矿层位—控矿构造—燕山期岩浆活动”三位一体找矿思路，但由于研究区地表地形崎岖、植被茂密，以往很少进行高精度大比例尺的综合地球物理调查，因此对隐伏的控矿构造、赋矿层位和火成岩体分布的认识远不能满足深部找矿的需求。.针对深部找矿的需求，本项目重点开展了保留近地表信息、构建全深度域速度模型、进行从真地表开始的深度偏移成像研究。主要解决了两个方面的问题：一是数据消除静校正量后回到地表；二是结合近地表速度建模建立全深度域的速度模型。我们将进行完反褶积后的地震数据重新恢复到地表，得到了包含了整个处理流程在地表上的地震数据；在速度建模方面，采用初至波波形反演获得浅层速度结构，采用常规处理手段获得深部速度结构，将二者拼合成统一的初始速度模型，用全波形反演和波动方程地表偏移距道集更新后获得全深度域速度模型，进行真地表叠前深度偏移成像。实际资料成像结果比常规处理结果有了巨大的改善，清晰地给出了3000m深度上的地层结构和断裂特征，使金属矿地震方法技术取得了显著进展。.实施了反射地震、CSAMT电磁法勘探、钻井岩芯采样与物性测量、大比例尺航磁资料处理等，其中，所采集的地震数据是本研究区首次开展的地震勘探剖面，所使用的航磁数据亦是本研究区首次获得的高精度大比例尺数据。采用地震真地表偏移成像技术、CSAMT二维带地形反演技术和航磁线性构造提取与三维反演技术，提取识别了剖面浅层逆冲推覆控矿构造和赋矿层位的反射地震特征，燕山期火成岩体的地震、电磁特征，以及控矿构造和隐伏岩体平面分布的航磁异常特征。在地质、物性等约束下，构建了剖面地质解释模型，包括浅层推覆构造、隐伏岩体分布和地层分布，推断解释了平面大断裂6条，次级断裂16条和三处隐伏岩体的三维分布。总结了推覆构造控矿的地球物理响应特征，建立了深部找矿的地球物理标志，为在外围和深部找矿提供了地球物理支撑。