Forward Theory Study Of Magnetometric Resistivity And Induced Polarization Methods

Magnetometric electric method is a magnetometric conducting electric prospecting method. It is used to analyze anomaly distribution and realize exploration by changing measuring potential difference between two surface electrodes of conventional electric methods to measuring magnetic field (total magnetic field and secondary magnetic field). Magnetometric electric method includes magnetometric resistivity (MMR) method and magnetic induced polarization (MIP) method. Magnetic anomaly of magnetometric electric method is created by conducting current in the anomaly body, and it is dependent on conductivity and electrochemical action of the target body. Three dimensional forward modeling has been realized by using finite difference numerical modeling method. By the forwarding modeling, it is found that amplitude of magnetic anomaly (primary field or total field) of MMR is relatively big, and amplitude of magnetic anomaly (secondary field) of MIP is much smaller than the former. Both anomaly forms not only can reflect exist of the anomaly bodies, but also have preferable corresponding relationship with relatively high or low resistivity between anomaly body and wall rock. However, there are great disparity between secondary field and primary field (or total field), and which shall be taken into consideration during measuring magnetic polarizability directly in practice work. Discussion for magnetometric electric method on getting over shielding layers and distinguishing group anomaly bodies has been made. While there are local high resistivity layer above anomaly body, current through the body will increase because of the high resistivity layer. As a result the magnetic anomaly will increase, too. The high resistivity layer shall not be infinitely great or close to surface, otherwise the layer will prevent the current entering the anomaly body and no anomaly will be produced. While there are low resistivity layer above anomaly body, amplitude of anomaly will be influenced greatly because of current decreasing through the body. In addition, magnetometric electric method can distinguish anomaly group bodies when resistivity contrasts between the bodies and wall rock are opposite, such as relatively high resistivity or relatively low resistivity. If the resistivity contrasts are same, magnetometric electric method has no predominance. In consequence, resistivity contrasts shall be taken into consideration for distinguishing anomaly group bodies by magnetic field.