2Dinversion for borehole magnetic data in the presence of significant remanence and demagnetization

Significant remanence and demagnetization alter the intensity and orientation of total magnetization,which complicates interpretation of magnetic data.To deal with the problem,we propose a method of inverting 2D magnetization vector distributions using the 2D borehole magnetic data.We firstly invert the magnetization intensity distributions based on magnetic anomaly amplitudes of borehole magnetic data. With the known magnetization intensity distributions,subsequently,we invert the magnetization orientation distributions by fitting the magnetic component anomalies.Both magnetization intensity and orientation are solved by conjugate gradients.And a preconditioned matrix is utilized to improve the inverse quality of magnetization intensity. All synthetic examples involving significant remanence and high susceptibility demonstrate that this method is capable of accurately recovering the magnetization vector distributions. The magnetization vector distributions comprehensively include the influences of induced magnetization,remanent magnetization and self-demagnetization.Therefore,it provides an effective approach to study the ore deposits when high susceptibility and significant remanent magnetization are present.