In deep-level South African gold and platinum mines, the standard way of mining is by developing footwall or hanging wall drives parallel to strike (the line formed by the intersection of a bed or vein with the horizontal plane). Cross-cuts are then developed perpendicular to strike until they intersect the reef. Mining then proceeds up the reef plane from level to level.
The geophysical challenge this presents is to define the reef plane in sufficient detail that once mining starts, it can proceed without any unexpected disruptions. Classically, geologists have mapped the reef plane from boreholes, outcrops and excavations. It is theoretically possible to achieve any desired resolution of the reef plane using higher densities of boreholes, but the cost is almost always prohibitive. Large dislocations that influence overall mine design are usually identified using the normal drilling pattern and from 3D seismic data. Knowledge of smaller dislocations can greatly improve short term tactical planning: typically, if a dislocation in the reef is less than three meters, it is possible to continue without redevelopment, while dislocations of more than 3m require redevelopment. Redevelopment takes time, and production is stopped during the process. If small dislocations can be mapped, miners can plan for the dislocations, lowering the cost of dislocations by lowering the extent of uncertainty about the rockmass.
Enter borehole radar
Borehole radar, an electromagnetic, geophysical tool that creates images of the subsurface by using short pulses of radio energy, is the best tool to identify production stopping dislocations. It is quick and easy to apply, and images dislocations in Witwatersrand gold mines and Bushveld platinum mines up to 60m from the borehole. It is most economically applied from boreholes like haulage and crosscut cover boreholes that would be drilled in any event.
Go Team South Africa
South African mines are deep and hot. Any tool used in our mines must be designed to withstand these conditions. Also, designing, building and utilising a tool locally has many other socio-economic spinoffs, like job creation, human capital development and the building of scientific expertise.
This was the thinking behind the design and building of a homegrown borehole radar system at the CSIR in 2001. The development and testing was done at such a rate that by 2002, it was a complete commercial system used in routine surveys. It was named the Aardwolf BR40 borehole radar system. The system is still in use to this day.
Designed for standard underground exploration holes (so it fits comfortably in a 48mm borehole), the radar is robust enough for routine work underground and is easy to use. It works in boreholes with high temperatures, which sometimes
exceed 70 degrees Celsius. The Aardwolf BR40 borehole radar system has a frequency (40 MHz) that offers the best
compromise between range and resolution for geological targets in the Bushveld platinum and Wits gold environment.
With rapid data turn-around (one week from provision) and novel interpretation software to augment mine geologist knowhow, the system can be deployed without needing support from the mine or its drillers.
The system is currently operated commercially by the CSIR, which is seeking partners for its survey business.