深海热液硫化物矿体3D瞬变电磁正演

The 3D transient electromagnetic forward modeling of volcanogenic massive sulfide ore deposits

深海热液硫化物矿体瞬变电磁的正演是考虑深海环境的全空间条件下三维体的涡流电磁响应.采用全空间矢量有限元法模拟计算深海热液硫化物矿的三维瞬变电磁响应,对硫化物矿体采用矩形单元模型剖分,应用Galerkin法推导有限元方程,先计算频率域响应,再通过Fourier反变换将其转换至时间域,得出深海热液硫化物矿矿体的瞬变电磁响应.并用双半空间模型的解析解检验了全空间矢量有限元法模拟计算算法和程序的正确性,最后按照等比例缩小电磁物理实验原则,比对数值计算和物理实验结果论证了全空间3D模型数值的正确性.结果表明:对于海水、矿体以及围岩复杂电磁边界,应用全空间矢量有限元法模拟计算深海热液硫化物矿瞬变电磁响应异常与物理模拟结果一致,而且计算方法简单精确,异常幅值明显,边界清晰.

The transient electromagnetic forward modeling of volcanogenic massive sulfide（VMS）ore deposits is to calculate the eddy currents electromagnetic response of a three dimensional body in the full space of deep-sea environment.We simulated the three dimensional transient electromagnetic response of the VMS deposits using full-domain vector finite element method.The ore body was discretized with brick rectangular elements.The finite element equation was deduced in frequency domain by employing Galerkin procedure,and the conversion to time domain is using inverse Fourier transform.We confirmed the validity of the full-domain vector finite element algorithm by comparing simulated results with analytical solutions of double half-space model.The results have a good agreement with each other which indicates that the vector finite element method is capable of solving whole space problem.In order to demonstratethe ability of the numerical method in calculating the response of VMS deposits containing complex boundary conditions,we compared vector finite element solution of a three dimensional electrical model with physical experiment results according to electromagnetic physical scale modeling rules.The comparison suggests that for the complex electromagnetic boundary of seawater,ore body and country rocks,the transient electromagnetic response of VMS deposits calculated by full-domain vector finite element method has same features with the physical scale modeling result.The vector finite element method is simple and its results are precise with obvious and clear anomaly response.