Q&A with Palabora Mining’s Robert Brazier, GMG Johannesburg Forum Speaker

Robert Brazier – Senior Geologist, Vertical & Technical Growth Division, Palabora Mining Company­ ­– will be presenting a case study on Cave Tracking of Lift II at the Palabora Copper Block Cave Mine at the GMG Johannesburg forum, April 2-3

Block caving hard rock underground mining method. This method uses gravity to its advantage; It involves undermining the ore and then following a process of controlled caving known as propagation. The ore is then removed from the cave. Block cave mining is cost-effective and presents many opportunities, but it is also a process that requires careful monitoring.  

We asked Brazier to describe a bit more about how cave tracking technologies work and why they are important.

What problems do cave tracking technologies aim to solve?

There are several challenges and risks associated with the propagation of a block cave. There is the risk of the cave not initiating or that it will stall. The cave shape and propagation have to be tracked to ensure that there is no ‘chimneying’ or the formation of an asymmetrical cave, which could lead to the reserves becoming unproductive.

There is also a significant risk of an air gap forming, which can lead to dangerous air blasts. This risk has to be carefully monitored and managed, as it has resulted in multiple fatalities at other block cave mines around the world.

How do these technologies work?

At Palabora Copper we have opted for an instrument array which includes network smart markers, sloughmeters, an open hole camera system and geophones.

The network smart markers and sloughmeters are installed in long drill holes, designed so that they are intersected by the propagating cave. The network smart markers communicate with each other through radio signal. The radio signal is lost once the marker has moved beyond a certain distance, indicating that the rock has caved. Sloughmeters consist of anchors spaced at 40m intervals and grouted in place. As the rock caves, the respective anchor is taken with it, severing the circuit and indicating the loss of the anchor.

The open hole camera system is used to lower a camera down strategically-placed drill holes and record the position of the cave-back. The seismic system at Palabora Copper consists of strategically-placed geophone sensors that record seismic events, making it possible to track the seismogenic zone, ahead of the cave-back.   The seismogenic zone consists of numerous on-going seismic events, induced by high stresses overcoming the inherent strength of the rock.

What are some of the key challenges with these technologies?

The challenge with the open hole camera system is the potential for holes to close ahead of the cave-back, which could prevent the camera from being lowered to the end of the hole. When the camera is lowered into the cave, there is also the risk that falling rocks will damage the camera.

This instrument array, combined with the instruments to monitor the Lift II production level, will also produce a large quantity of data. The challenge here is to be able to manage and interpret the data promptly and accurately to enable the technical team to make correct decisions and act appropriately to any identified risks.


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