Archean terrain "North of 60"
At right is the actual field wiring diagram for a 3D E-SCAN survey north of the Arctic Circle, where lakes occupy a large portion of the study area. Many individual grid stations were installed from the GPS-equipped inflatable boat, by pulling a wire from shore to the grid position where an attached heavy metal fishing weight was lowered to lake bottom to serve as an electrode contact.
In the wider area of the lake, two floating hubs provided access to a total of 32 lake-bottom electrodes sites. Each hub employed a master duplex signal wire connected to the main grid wiring network on shore, and a separate current feeder wire. The extremely fast shooting of these 32 mid-lake stations made up most of the extra time required to position and install the floating base's lake-bottom electrodes by boat.
On this project, the client's exploration schedule could not accommodate a winter through-ice E-SCAN survey. The water-grid installation maintained perfect continuity in the true 3D field data set (uniform distribution, high density, and multi-directional data set characteristics), as if the lake wasn't there. Time, cost, risk?
Above is the field wiring diagram for a 3D E-SCAN survey to test resolution of unconformity uranium target features, in an area dominated by Waterbury Lake. Year-round road-accessible infrastructure at the nearby Cigar Lake mine helped to make this an easy "in winter" choice for survey timing. Snowmobiles easily traversed the lake with GPS guidance, to install and wire the electrode stations on the 400 metre spaced survey grid. High-speed wire deployment from disc-braked , damped spoolers made laying out the wire a simple task, and gas-powered re-winders made recovery and cleanup go fast. A powered auger easily drilled through the 1 metre thick ice, allowing electrodes to be lowered into the lake-bottom mud, at each station.
The lake installation maintained perfect continuity in the true 3D field data set (uniform distribution, high density, and multi-directional data set characteristics), as if the lake wasn't there. Time, cost, risk?
At right is an example of how 3D E-SCAN would wire a depression (a pond or small lake) suspected of being the site of a buried kimberlite pipe.
In winter, the frozen surface would allow on-ice wiring and through-ice, pond-bottom electrode installation.
Time, cost, risk?