An analysis of geophysical and geological data from the Gallen test site, Quebec, Canada

The MEGATEM^II system was flown over a test site containing the Gallen deposit. The measured response is consistent with the known geology and shows a rapid decay indicative of a poor conductor. Comparisons with older GEOTEM and INPUT data are problematic, as each dataset was acquired at different stages in the mining of the deposit. Although the GEOTEM data has the best signal to noise, the MEGATEM data were acquired after a significant portion of the deposit was removed. The MEGATEM data have been use to assess the impact of noise sources. Tests with the transmitter off and on show that the power lines have a detrimental impact on the data; however, most of the response of power lines is associated with currents induced in the power line by the transmitter. A new method for rejecting power lines noise gives good results compared with the standard method of processing the data. Modelling of the data shows that the water in the open pit has an effect on the early-time data (primarily the z component). The impact of the fence that surrounds the open pit is not considered to be significant. © 2005 Society of Exploration Geophysicists.