After blasting, a Load Haul Dump (LHD) loader collects the broken ore which is then taken to the primary crusher to further reduce the size of the ore material. The ore material should be small enough to pass through the crusher otherwise large fragments will jam the crusher creating a bottleneck in the production line.
The driver of the extraction vehicle makes an assessment of the size of the fragments at the draw. If a fragment is too big for the primary crusher, the collection of the ore material is suspended and the area is closed until a secondary crusher crew arrives to break the large fragment.
Cadia East (near Orange) Panel Cave 1 Primary Crusher (Image: Newcrest Mining Limited)
The driver can only see large fragments at the surface in the draw as shown in the following figure.
Draw Point in an Underground Mine
The challenge is to determine whether large fragments that cannot be seen are present inside the pile before the LHD vehicle arrives.
Ground Penetrating Radar (GPR) is an imaging technique that uses radar pulses to probe the subsurface.
Chris Lewis from the CSIRO Materials Science and Engineering Division demonstrating the use of a GPR unit (Image: Newcrest Mining Research Laboratory - CSU)
GPR was used to identify large fragments within the pile by looking at the reflected radar signal: small fragments surrounded by air pockets have a different electromagnetic signature compared to a large rock fragment. The group developed sophisticated algorithms to refine and enhance the analysis of the GPR images.
Identifying large fragments at the draw point before collection of the ore allows the operators of the mine to plan the closure of the draw, prevent unnecessary vehicle movements, and equipment shutdown. This technique reduces costly shutdowns and enables a more efficient operation of the mine site.