Technical Papers - Airborne Electromagnetics – Case Histories

A Comparison Between Old and Recent Airborne Time-Domain Electromagnetic Surveys Flown in the Chibougamau Region, Eastern Canada

Keating, P., Dumont, R., Geological Survey of Canada, Houle, P., Ressources naturelles et Faune, Québec

Abstract

The Chibougamau region, located at the eastern end of the Abitibi Greenstone Belt, north-western Quebec, Canada, has been flown by various electromagnetic (EM) surveys. Government-funded surveys were flown to help base metal exploration and data are available in the public domain. A time-domain EM survey flown in 1972, resulted in the discovery of the Lemoine mine. As a result of this success the rest of the region was systematically surveyed by time-domain surveys between 1977 and 1980. A modern time-domain EM survey covering 9000 km2 was flown in 2006. This recent survey allows assessment of the benefits of flying a state of the art EM system over a previously surveyed area. A first comparison, strictly based on the number of EM anomalies, reveals that the recent survey detected 25% more anomalies than the older ones. A second comparison is based on interpreted depths derived from the recent survey data compared to what is known of the depth of penetration of older systems. More than 1000 anomalies are interpreted to have their sources deeper than 75 m, and more than 450 have sources deeper than 100 m. This interpretation is based on a thin vertical rectangular plate model in a resistive host rock. This is a reasonable hypothesis as the geology of the region is sub-vertical and very little conductive overburden is present. The depth of penetration of older systems was likely to be between 75 and 100 m and we conclude that the recent survey detected at least 400 anomalies related to deep sources. However, this number of new anomalies does not imply new exploration targets, since a given conductor generally produces more than one anomaly due to its length and dip. Some new anomalies are due to shallow sources. Modern EM surveys detect new exploration targets at depth and, also, shallow conductors missed by previous surveys

Poster presented at Exploration 07.  The expanded abstract is available on the conference CD or DVD.

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