GROUND PENETRATING RADAR (GPR) IN INDUSTRIAL MINERAL MINING

Karst features and other natural irregularities in stone can cause problems in successful economic exploitation of deposits. Caves can pose safety, hydrologic, and environmental problems in crushed stone quarries. Karst features of many sorts can cause loss of reserves, foster operational problems, and affect final uses of any limestone. Techniques for predicting occurrences and locations of problematic features would be very useful to quarry operations.

Ground Penetrating Radar (GPR) was used at several active or planned crushed stone quarries to look for karst features. Large- to moderate-size solution features were readily observed up to 15 meters deep using a 50-megahertz instrument on bedrock surfaces. Using a shielded 250-megahertz machine reduced typical penetration to 4 to 6 meters but increased resolution. Mud-filled features were easily outlined as were open passages. Examples of known wild caves not exposed by mining were also observed using GPR. In noncarbonate applications, the technique was useful in locating concretionary features (~1 meter) in a dimension sandstone quarry. Ground Penetrating Radar was able to outline deleterious clay-rich zones and indicate very coarse materials in sand and gravel operations. Cultural features such as pipes, graves, and buried vaults that can affect mine development are also easily delineated. Depth of penetration is the primary constraint in GPR but using longer wavelengths improves depth of penetration. Clay-rich soils, especially if wet, inhibit GPR's usefulness in defining overburden thickness. Despite limitations, GPR can be cost-effective in quarry planning and development of industrial minerals mines.