Ground Penetrating Radar Surveys

Knowledge in the Field

Ground Penetrating Radar (GPR) surveys are used in placer exploration to rapidly map the top of bedrock and thus determine the location of paleochannels. Radar reflections occur at the boundary between materials with different dielectric permittivity. This property is largely controlled by liquid water content. Relatively dry bedrock and ice have low dielectric permittivity and water saturated sediments have high permittivity.  In addition, clays retain bound water in the liquid state well below freezing and consequently clay alteration or black muck appears as a distinct reflector even when frozen.  GPR surveys can be conducted rapidly on well-prepared lines but are limited in depth penetration to 20 to 30 m in most situations.

AGL Delivers

AGL pioneered the application of GPR to placer exploration in the North in 1989 with a GSSI system, and have conducted extensive tests of GPR for placer exploration, published as Yukon E&GS Open File 1994-1. We offer GPR surveys with RAMAC and Pulse EKKO radars at frequencies from 25 to 200 MHz.  We also have unique experience in applying GPR surveys to kimberlite exploration. 

The radargram below shows a good response in "Klondike-type" placer deposits where black muck (upper portion of drill logs) overlies White Channel gravel on top of bedrock.  The auger holes shown in the section all stopped at the top of bedrock and the GPR survey provides excellent definition of bedrock in this situation.  In other cases, it does not work as well.  Surveying in thawed clay is a particular problem as the radar energy is absorbed within a few metres in this environment.