论被动源磁电勘探理论

本文从麦氏方程出发,运用电流磁场的等效理论阐明了在磁电勘探中,当矿体的二次极化电流具有垂直对称轴分布时,在地表面及以上空间中任一点的磁异常场（H）均等于零。因而,具有任何垂直对称状电化学矿产模式（石油、天然气、地下水及金属矿床等）的磁电勘探法异常场线积分均不存在。此外,由于对各种形状和任何极化倾角的矿体情况,地表面上均无电流密度垂直分量（i_n）存在,故地表面上异常场线积分均为零（∮_L H·dL=0）。因此,磁电勘探法不具备在地面上寻找此种矿产的物理前提。 本文还对倾斜极化球体和柱体的磁电勘探异常进行了计算,给出了主剖面上理论曲线的异常分布规律,指出了磁电异常的数量级。同时,还对井中磁电异常的分布规律给出了计算资料。为了对比,也对相应条件下的自然电场异常做了计算,指出了电场异常与磁场异常之间的不同特点及其对实际找矿的意义。

ON THE THEORY OF MAGNETO-ELECTRIC PROSPECTING UPON PASSIVE SOURCE

It is shown, by use of the principle of equivalence, that when the induced polarization current of the ore body is symmetric with respect to a vertical axis, the anomalies of the magnetic field （H） on the earth's surface and at any point in space over the surface are all equal to zero, so the line integrals of the anomalous fields in the magneto-electric method for any electro-chemical mineral models which have vertical symmetric axis （oil, gas, groundwater and metalliferous deposits） will not exist. Furthermore because there is no vertical part of current density on the earth's surface, sothe line integrals of anomalous fields are also all equal to zero （namely ∮_L H·dL=0）for any ore body with any shape and polarization angle. Therefore, the magnetoelec-tric method cannot be applied for prospecting such ore bodies on the earth's surface. In this paper, we have also calculated the anomalies of magneto-electric prospecting for spheres and cylinders which have dipping polarization, we have calculated the theoretical curve for the anomalous distribution on the main section and the order of magnitude of the magneto-electric anomalies. Moreover, we have also computed the distribution of anomalies in wells. For comparison, we have calculated the anomalies of spontaneous potential under corresponding conditions and pointed out the different features in the anomalous electric field and the anomalous magnetic field, as well as their significance for prospecting.