The South African mining industry requires a paradigm shift in its fundamental approach to mining processes to ensure that it can move away from the use of explosives, says diversified miner Sibanye Resources safe technology and innovation project engineer Alex Fenn.
He argues that explosives are currently the only financially and logistically viable method of breaking the required volume of ore that underground mines need to extract on an ongoing basis.
“We base our entire production cycles on these instantaneous blasting procedures,” Fenn points out. He notes, though, that, since explosives induce seismicity and generate noxious gases, mines are required to evacuate shafts to allow time for them to return to acceptable seismic and environmental levels. This results in significant periods inactivity, hampering continuous operations.
Fenn states that what is required is a localised rock breaking technology that will still be able to impart a suitable amount of energy into the rock. For this to happen, it is likely that mines will need to have some form of mechanised platform on which to base this system.
This system will have to be significantly larger than standard rock drilling systems. However, he remarks that the drawback of many legacy gold mine operations in South Africa is that they usually have steep-dipping orebodies and narrow reefs. Therefore, Fenn highlights, the proposed platform will have to be compactly designed to fit into these narrow work areas to avoid increasing material dilution.
To address these challenges, Sibanye is developing the Multi-Track (MT)1000, which has a 1 t payload and weighs about 3 t. The MT1000 is 930 mm high and has four independent track assemblies, which are capable of three different degrees of motion, including drive, track assembly rotation and track assembly articulation.
Fenn elaborates that this allows for a high level of manoeuvrability within the prolific support structures at South Africa’s deep-level gold mines.
He comments that the MT1000’s drill and break attachment consists of a 4.5 kW drifter, along with a feather-and-wedge-type breaker. Further, Fenn explains, the machine aligns itself with the rock face, while driving parallel to it. The MT1000 drills a 46-mm-diameter hole, and then indexes the breaker to the hole’s position and inserts it; thereafter, the breaker imparts lateral force to the rock.
He remarks that, in terms of the testing that Sibanye has done to date using the machine, it has found that the MT1000 breaks rock vertically along the axis of the hole and at about 45° to the stress lines.
Fenn believes that mineworkers will be able to work “fairly closely” to the machine because even though there is a considerable amount of energy being imparted to the rock face, it is quite a “casual process”. Nonetheless, he notes that there have been a few instances during the trials where there have been limited ejections of rock.
Therefore, Fenn recommends the erection of some type of temporary partition between the position of the machine and the location where general work is being undertaken.
Moreover, he highlights that the use of this machine will enable mines to continue to perform other regular tasks, while the drilling and breaking are being undertaken.
“If the MT1000 trials are successful, Sibanye will be able to ensure 24-hour, continuous operations, provided we do not have to use scrapers and rigging.”
Therefore, Fenn says, to complement the drill-and-break process, Sibanye has developed the MT100, which is an ultralow-profile mining machine with a 100 kg payload.
He states that the machine’s design is similar to that of the MT1000 and has a battery-driven platform, with its attachments consisting of an ultra-fine sweeper and a dozer blade. Fenn remarks that it will enable mines to complete the stope cleaning process within 24 hours, which is usually restricted to a short three-hour window, owing to the need to get back into production quickly, as a result of the time lost waiting after blasting.
“These machines will not only assist in greatly increasing productivity at our mines, but also ensure a significant improvement in health and safety standards at mines, as mineworkers will be removed from hazardous work areas, [including] the stope face.”
Additionally, Fenn highlights that the MT1000 and the MT100 will allow for shift cycles to be adjusted to ensure an ‘always operating’ philosophy is adopted. “This may entail four eight-hour overlapping shifts at mines. This will also help address the challenge of worker fatigue at mines,” he adds.
Fenn mentions that these machines will ensure improved rock fragmentation, which will result in significantly less gold being lost and better mine call factors. He also says there is no significant energy imparted to the hanging wall, which means, at some point, a mine could even reconsider its support installations.
He tells Mining Weekly that Sibanye is seeking to complete the research and development and trialling of these technologies by the end of 2017 and implement the mechanisation of suitable sections of its mines within the next three years.
The company’s long-term goal – which it hopes to achieve within the next 8 to 10 years – is to further develop the remote operation of this technology to enable the company to extract resources that it currently cannot reach using conventional mining methods. These timelines are all dependent on the successful qualification of the technologies.
Meanwhile, Fenn enthuses that the use of these technologies will improve standard industry asset availability, when referring to shaft infrastructure, from its current level at about 27% (owing to downtime as result of blasting) to almost 100%. “This means that mines will have a controllable, steady flow of material, which is very important because mines will, to some extent, be able to manage their output per panel to match the economic factors that are influencing the commodity at the time.”
Moreover, Fenn contends that the use of these technologies will ensure that fleet size and infrastructure that is needed to transport material can be significantly reduced because mines will no longer need to transport large volumes of rock in short sequential periods. Large locomotives that are commonly used at mines, can be replaced with smaller overhead conveyor systems, which will reduce a mine’s maintenance requirements, he adds.
“Having a controllable flow of materials will significantly reduce the operating costs throughout the mining and processing phases of the operation,” Fenn says.