退磁作用对磁测资料解释的影响

退磁作用使磁异常幅值变小,形态畸变,影响磁测资料反演解释的地质结果的准确性。用有限元法数值模拟磁性体在考虑退磁作用下的磁场,以二度水平圆柱体理论模型为例,研究退磁作用对磁异常的影响。当磁化率κ≥1.0 SI时,考虑与不考虑退磁作用,异常极大值偏差可达1 300 nT以上,相对偏差可达30%以上,因此认为退磁作用的影响很大,不可忽略。青海尕林格铁矿区磁测资料的反演实例说明,忽略退磁作用将导致反演的矿体体积偏小,影响钻孔的布置和资源储量的评价。

THE INFLUENCE OF DEMAGNETIZATION ON MAGNETIC DATA INTERPRETATION

Because demagnetization reduces magnetic anomaly amplitude and distorts the shape,it affects the accuracy of geological results inversed and interpreted by magnetic data.Exemplified by a horizontal and theoretical 2D cylinder model,this paper simulated the magnetic field in consideration of demagnetization and by using the finite element method and studying the influence of demagnetization on magnetic anomaly.When the magnetic susceptibility κ is greater than 1.0 SI,the anomaly maximum deviation reaches up to 1 300 nT and the relative deviation is more than 30%,whether demagnetization is considered or not.It is thus concluded that the remarkable influence of demagnetization must not be ignored.Besides,the magnetic data inversion conducted in the Galinge iron mine of Qinghai shows that ignoring the demagnetization will underestimate the size of the inversed ore body and mislead the drilling design and resource reserves estimation.