As part of continuing research aimed at the detection of subsurface tunnels and voids, the U.S. Bureau of Mines recently completed a cooperative study with the U.S. Geological Survey at a surface gold mine in the Black Hills mining district of South Dakota. The occurrence of older, poorly mapped mine workings in the section create a consistent health and safety concern for mine employees as well as economic concerns about potential damage to equipment during daily operations at the mine. Accurate knowledge regarding the location of these abandoned tunnels prior to interception by the current mining operation would be beneficial. Previous research efforts on site have demonstrated the suitability of several surface geophysical technologies in detecting shallow workings which present an immediate problem in the safe conduct of the mine operation. Another concern is the existence of deeper abandoned mine tunnels, which occur further in advance of the surface mining operation. In the design and development of a new mine pit, the placement of access roads over a tunnel would be hazardous, due to the volume of traffic and the weight these haulage trucks can carry. In this study we evaluate cross borehole radar tomography methods which might be used to image mine openings in the deep subsurface, and lead to more prudent placement of pit haulage roadways. A pulsed radar system was used to collect both velocity and amplitude information about local rock conditions, and multiple borehole data allowed for the use of 3-D imaging techniques.