Abstract

Dry salt has a very low electrical conductivity which permits radio signals to be transmitted through substantial thicknesses of salt with little attenuation. Radar sounding experiments conducted in several potash mines in Saskatchewan, Canada confirm that radar is an effective method for probing salt environments. The experiments had two main objectives: namely, to assess the utility of impulse radar for mapping stratigraphy in the salt beds above, below, and beside mining tunnels and to determine the electrical character of the potash beds in situ, since little information was available on the radio-frequency properties of potash ore.The experiments were conducted with an impulse radar system using antennas which radiated pulses having center frequencies between 100 and 1000 MHz. The higher frequency antennas detected thin clay beds and stress-relief cracks to depths of several meters. Sounding for deeper structure known to exist at ranges of several tens of meters was not always successful. The lower frequency antenna systems were found most useful for deeper sounding; in some instances known geologic horizons were detected at depths of up to 20 m. Deeper structure was frequently masked by shallow, high-reflectivity stress-relief cracks.The potash deposits were found to have a bulk dielectric constant in the range 5 to 6. In many areas, the evaporites have a significant clay content which governed the signal attenuation. Depth of penetration of the radar was generally greater in areas of lower clay content.

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