Magnetic induced polarization - using new technology for greater detection capability of deep and elusive mineralization

Abstract

The MIP method was first proposed by Siegel (1974) as an alternative to electrical IP but has not seen extensive commercial application. Most likely, this is due to the inherent difficulties in measuring very small magnetic fields at the low frequencies necessary for MIP. A further complication is the presence of magnetic noise from both natural and synthetic sources which can make it difficult to distinguish the very small MIP magnetic fields from the background noise. With the relatively recent availability of Super Conducting Quantum Interference Devices (SQUID) it is possible to measure low frequency magnetic fields with very high sensitivity. By utilizing two SQUIDS - one for measuring over the target area and a second which serves as a remote reference station, we are able to significantly increase the signal to noise ratio. Using advances in acquisition technology with GPS time stamping, we record data from both SQUID locations and the input current, then synchronize the time series and perform noise cancellation to accurately determine the MIP response. Similar to traditional electrical IP, MIP has particular application for sulphide-associated, disseminated and vein gold and base metal deposits. However, the higher sensitivity of SQUID MIP, and the inherent ability of MIP to see through conductive cover, means that it can detect these deposits to greater depth, in more difficult environments, and with greater resolution and discrimination. We present our equipment, methods and a number of field trials using both frequency and time domain methods to analyze the MIP responses from porphyry copper, vein gold and unconformity uranium ore bodies.