Evaluation of the efficiency of several airborne electromagnetic systems: Exploration implications

A comparison of data from INPUT, GEOTEM, and MEGATEM airborne electromagnetic (AEM) systems over the Aldermac deposit, Québec, Canada, was undertaken to evaluate the relative efficiency of these systems for the detection of small, deep conductors. The Aldermac orebody was mined between 1933 and 1934 to a depth of 200 m. A deeper mineralized zone was discovered in 1987. The MEGATEM1I system was used to acquire 90- and 30-Hz data over the deposit in 2003 as part of a research project. These MEGATEM 11 data were compared with data acquired by other AEM systems (GEOTEM and INPUT), and the results show that the MEGATEMII response is ten times larger than the other systems. For the dB/dt response, 30 Hz gives a better signal-to-noise ratio, whereas 90 Hz has a better signalto-noise ratio on the B-field. The data were evaluated by numerical modeling. The deposit was best represented by a complex model, comprising two weakly conductive bodies to approximate the alteration halo, two deeper prisms representing known orebodies, and three bodies ranging in thickness from 3 to 6 m and in resistivity from 12 to 20 ohm·m, representing the chargeable overburden. This implies that the MEGATEMII system is able to see a small conductive body at more than 200 m depth in an area where the response is contaminated by conductive overburden. © 2009 Canadian Institute of Mining, Metallurgy and Petroleum. All rights reserved.