Wilkinson told International Longwall News that the lower than expected productivity of some longwall operations in Australia and the increase in productivity of medium to thick seam bord and pillar operations in South Africa is reopening the debate as to whether bord and pillar is a viable alternative to longwall mining.
ILN: How do you think Australian mining conditions and culture are different to South Africa?
CW: Mining conditions differ in that many seams in Australia tend to be deeper than in South Africa, often due to the dip of the seam. SA coal seams do not have as many faults as in Australia but are frequently intersected by igneous dykes and sills which are too hard to cut through and require blasting to mine through them. Rib stability in SA is extremely good compared to the majority of Australian mines. The underground coal mining culture in SA is based on bord and pillar mining as opposed to Australia where it is based on longwall mining. Australia has a high level of skills and everyone is numerate and literate. In SA many mine workers do not read and write confidently, which limits some forms of instruction and training. SA also has a very high HIV infection rate which impacts on the continuity of people in the workforce.
ILN: What current conditions do you believe make Australian coal reserves suitable for increased bord and pillar operations?
CW: Longwall mining requires large contiguous reserves without a lot of faulting. Many reserves in Australia do not meet these requirements because they are not large enough to support a 15-year, 6 million tonne per annum longwall or have too many faults to be able to mine productively with longwall techniques. Some investors are uncomfortable with the level of risk and high capital investment associated with longwall mining and would prefer to use a lower risk, lower capital method, even if this means the cash cost profit is lower.
ILN: Can you expand on why the flexibility and production continuity of bord and pillar is attractive to investors?
CW: Experience has shown that many reserves when mined are far more structurally complex than the original geological exploration at feasibility stage indicated. When you have one longwall and it intersects a fault, the complete production from the mine is affected and in some cases may even stop for several weeks or months. This creates many credibility and financial difficulties for the mine. Conversely, [with] a bord and pillar mine with between four to six sections, generally only one or two sections are affected by faults while production continues in the other panels.
ILN: You said many reserves being considered for new underground coal mines (particularly in Queensland) are structurally complex. Why would a bord and pillar operation be more effective?
CW: The impact of faults on bord and pillar sections is usually less than on a longwall and the panel can negotiate its way through the fault without catastrophic consequences.
ILN: Do you think coal companies in Australia fully recognise the benefits of bord and pillar mining? Why do you think it is not as common as in SA?
CW: Bord and pillar has a stigma as being a high-cost and low-productivity method compared to longwall. This may have been true 10 years ago, but in the last five to six years bord and pillar productivities in SA have increased significantly, and in some cases one continuous miner section is producing up to 1.4Mtpa and the industry benchmark is 1Mtpa. It is now time to review the trade-off between CAPEX [capital expenditure], OPEX [operational expenditure] and risk between longwall and bord and pillar in some reserves. Longwall has been perceived as a safer method than bord and pillar but this is also subjective and requires review. Many reserves in Australia are not suitable for bord and pillar due to depth, roof and/or floor conditions and in seam gas. However, shallow reserves – which are not ideal for longwall mining – are being considered for bord and pillar operations. The reluctance to use bord and pillar is also one of familiarity and that there are not a lot of people in the country with bord and pillar experience.
ILN: What are the cost benefits in choosing bord and pillar operations over longwall mining for medium to thick seams with complex faults?
CW: The primary benefit of bord and pillar mining is that for an equivalent production the capital cost of a bord and pillar operation would be 45% to 65% of that of a longwall mine. The operating costs may be 30% to 60% more than a longwall, but the risks are significantly less and production variances are very low compared to longwall.
ILN: You said the quantity of labour required for bord and pillar mining has not been able to compete with high-productivity longwall operations – how would this work in the current mining environment of skills and labour shortages?
CW: Experience in SA indicates that it is much easier to train an inexperienced person for bord and pillar mining than longwall. In longwall a small error or mistake can have huge consequences for production and cost of the operation. In bord and pillar mining the consequences of mistakes are less significant. However, in both cases safety remains paramount.
ILN: In what situation would you recommend using bord and pillar to gain information on the geology of a reserve to determine the viability of future extraction of deeper reserves by longwall?
CW: The application of bord and pillar for trial mines really has to be considered on a case specific basis as there are numerous variables and drivers to consider. However, if a coal resource has significant reserves less than 200m below surface and there is either too little information to determine if the reserve is faulted or that the structural interpretation suggests that the reserve is not suitable for longwall mining, then a bord and pillar trial mine may be a suitable option. In the current market where prices will allow a higher operating cost to make money, and approvals do not require subsidence to be considered, then implementation of a bord and pillar trial mine may be an attractive option.
ILN: What can Australian miners learn from SA in terms of bord and pillar mining?
CW: There has been a perception that the SA coal industry has a high production due to using more labour in section and having less onerous safety standards. However, this is not correct.
The main reason that SA has very productive operations is a greater focus on process management and less on customising technology. There are many learnings which could be transferred to Australia. Similarly, there are many cases where Australian systems and technology are being applied in SA to good effect.