Exploring to Depth in the Shadow of Headframes

Brownfield (near-mine) mineral exploration activity is at a record high – driven by the desire to mitigate risk in these uncertain economic times and the old adage that "the best place to explore is in the shadow of a headframe.” Many companies have purchased “old” mines to gain access to mineralization that was “missed” with previous generations of geoscience technologies and to assess new targets. Today, new deep geophysical technologies are assisting in exploration, ore delineation and ground sterilization.<br>Historically, however, it has been difficult to apply geophysical techniques around mines. Cultural noise, scheduling, electrical noise, remoteness and resistance to new technologies are some of the traditional obstacles (to performing geophysical surveys in brownfield areas) that have been overcome. One of the new technologies that has proven itself is deep electrical imaging -- made available thanks to the distributed acquisition system (DAS) technology. DAS technologies are characterized by a large multi-channel, fixed receiver array and several other factors that together contribute to improved depth of penetration, data quality and detectability. In this paper, we review the components and capabilities of DAS, focusing on one system in particular, for brownfield work, including near-mine and minesite applications. Three case studies, two from porphyry copper environments in western Canada and a gold project from Bulgaria, are presented. These case studies represent the state-of-the art in geophysics for brownfield work and are a novel application for current DAS technologies.