A test of ground penetrating radar (GPR) was conducted on 10 placer deposits throughout the Yukon in March 1993. At each site, profile surveys were conducted near known depths to bedrock (drill holes, shafts or excavations), overburden GPR velocities were measured with common mid-point (CMP) velocity surveys and overburden resistivity was measured with horizontal loop electromagnetic (HLEM) resistivity soundings. Survey sites were located in frozen deposits in unglaciated terrain, in thawed deposits in glaciated terrain and in frozen deposits in glaciated terrain.
In frozen unglaciated deposits in the Klondike and Moosehorn areas, GPR penetration varied from 10-28 m and averaged 19 m. Signal attenuation in thawed black muck and scattering within boulder layers limited penetration at two sites to about 10 m. The weathering of phyllitic and schistose rocks to clay enhances bedrock reflections; weak bedrock reflections were recorded due to a lack of dielectric contrast in deposits underlain by resistant bedrock. GPR performance is enhanced by surveying during winter or late spring when the zone of seasonal thawing is thoroughly frozen. Under optimum conditions, strong continuous bedrock reflections were recorded over distances of several hundred metres and accurate bedrock mapping was possible with a minimum of confirmatory drill holes.
