High Precision Raise
Anglo Platinum is making good progress with its Townlands Ore Replacement Project (TORP), which will extend the life of the shaft from 2010 to 2027, in the process saving several thousand jobs.
The project includes the sinking of a new ventilation shaft complex – consisting of three separate 3.8m diameter shafts – to a depth of just over 800m using advanced raise boring techniques. One of the shafts is now complete and, according to contractor Murray & Roberts Cementation, the pilot hole was drilled to an accuracy which represents a world record on a shaft of this depth.
The Townlands shaft is one of the oldest in the Anglo Platinum group and for many years has been one of the main producers within Anglo Platinum’s Rustenburg Platinum Mines (RPM) Rustenburg Section operation.
The original Townlands vertical shaft has been extended in recent years by what is known as the Townlands 2 decline cluster, designed to handle ore as well as men and material from the Merensky reef horizon and replace the depleted Merensky mining levels in the vertical shaft.
Under the current Townlands Ore Replacement Project, the development of the declines is continuing but the entire project has been rescoped to allow the extraction of not only the deeper Merensky reserves but also the deeper UG2. While this dual extraction strategy is not new to South Africa’s platinum mining industry, it is certainly a ‘first’ for Rustenburg Section.
The project manager for TORP is Ashley Lalla, who, remarkably (given that he is in charge of a major capital project), is only 35 years old, has only been with Anglo Platinum since 2003 and whose background is in electrical engineering (with Eskom) rather than in mining.
“In 2005 I came on board at Townlands,” he says, explaining the background to the current project. “It soon became apparent that the strategy of extending the declines simply to extract Merensky ore was not optimal. For example, there was a major mismatch between the hoisting capacity within the vertical shaft, on the one hand, and the achievable UG2 mining rate in the vertical shaft and the Merensky mining rate in the declines, on the other. In addition, the belt serving the decline cluster has a capacity of 120kt/month – again a mismatch, since the Merensky in the decline can only be mined at a rate of about 60,000t a month, which is half the belt capacity.”
Lalla says that the more he and his team studied the project, the more apparent it became that the deeper UG2 resource at Townlands needed to be factored into the equation.
“The main decision then was whether to put in a separate decline for the UG2 or use the existing decline cluster. We decided to go for the latter solution, which meant that the UG2 gets a free ride from a capital perspective. Once we had reconceptualised the project, we then went into the prefeasibility and feasibility stages. The project then went to the board and was approved in February last year. In total, the time from concept to approval was about 18 months, which was an achievement in itself – the process would normally take from 18 to 24 months.”
According to Lalla, the new extraction strategy for the Townlands shaft will ultimately see the vertical shaft operating at its full capacity of 220kt/month, consisting of 160kt/month of UG2 (drawn from both the vertical shaft and the decline system) and 60kt/month of Merensky (from the decline).
“In essence, the TORP increases the overall value of the Townlands shaft, while at the same time supporting the Rustenburg Section Strategy,” he says. “The project allows us to safely exploit the UG2 reserve in the decline shaft to make optimal use of the overall ore tonnage capacity at Townlands and also enables a major extension of mine life. Production is planned so that the vertical shaft and the decline system mine out at the same time.”
In terms of the TORP, the Merensky and UG2 will be co-extracted in the decline shaft area, with the Merensky being mined from 25 to 28 level and the UG2 from 15 to 28 level.
The mine design is based upon and benchmarked to the current Townlands shaft production areas and the mine layout is conventional scattered breast mining. In all cases, the Merensky infrastructure will be used as a basis to develop and open the UG2 resource. The downside to this is that the Merensky infrastructure is not optimally spaced and placed for UG2 extraction. Nevertheless, the benefits are considered to far outweigh the disadvantages. Selective attacking points on the Merensky are being used to open-up the UG2 areas. The UG2 levels which will be opened up from the Merensky are 15 level, 19 level, 21 level, 23 level, 25 level, 26 level, 27 level and 28 level.
Lalla says one of the noteworthy aspects of the project has been the trust that Anglo Platinum has placed in a generally young team which could intially have been deemed to be short on collective experience.
“This is my first mining project and many of my colleagues, although experienced in the mining industry, were at the time they joined the team new to the project world,” he notes. “But we all have a great deal of self-belief and I think that the results of this are evident in the good progress we are recording on the project. The teamwork we have is excellent and is well complemented by the support received from the wider organisation, in particular Dr Hein Jantzen, Programme Manager for the Rustenburg Projects.”
He also notes that the TORP is a ‘brownfields’ project, which means that the TORP team is having to ensure a smooth interface with existing mining operations at Townlands.
The TORP has created a demand for additional ventilation in the lower decline area which will be met by a new dedicated downcast shaft system carrying 600kg/s of air with 8MW of surface bulk cooling. The cooling will be supplied by a standard packaged refrigeration machine utilising a centrifugal compressor and R134a as a refrigerant. The shaft system is located approximately 2.8km from the main Townlands vertical shaft. It will intersect the decline system on 26 level (821m).
Says Lalla: “The initial plan was for a single 5.6m diameter shaft to be conventionally sunk from surface. But the problem was that our geotechnical investigations indicated that any shaft that was greater than 4.1m in diameter would require extensive support. We eventually decided that the best solution would be to go for three narrow shafts, each of 3.8m diameter, that would not require any lining. An advantage of this approach is that it allows us to get some much needed ventilation down to the underground workings well in advance of completion of the entire shaft complex. In addition, shafts of this diameter are easily raise bored. This obviates the need for blasting – and blasting was an issue given that the ventilation shaft complex is located only half a kilometre from the nearest housing.” He adds that the shafts are spaced 28m apart, centre to centre.
The shaft-sinking contractor for the shafts is Murray & Roberts Cementation, which has its own in-housing raise-boring expertise – in fact, the group can probably claim to be a world leader in raise-boring, given its depth of experience in this field. It has deployed a Wirth HG330 SP raise-boring machine on the contract. There are only five of these machines in operation worldwide, four of them with Murray & Roberts Cementation (two in South Africa, one at Bulyanhulu in Tanzania and the fourth in Australia).
While the use of a raise borer is solving problems it is, at the same time, posing some challenges. Says Stephen Delport, senior site supervisor for Murray & Roberts Cementation: “The pilot holes for these three shafts are calling for an accuracy which is exceptional. The holes have to link up exactly with three ‘cubbies’ on 26 level, which were excavated in advance of the start of boring operations. On the first hole, the only one we’ve completed so far, we were off by no more than 50mm over a distance of over 800m. Normal deflection is 1% of total length, which gives you some idea of just what we’ve achieved. We believe we’ve set a world record with the first pilot hole – it’s the least amount of deflection achieved on a hole of this depth.”
To achieve the accuracy, Murray & Roberts Cementation is making use of directional drilling technology from the German company MICON. Murray & Roberts Cementation has contributed to the development of the system and has been using it for several years now on contracts where minimum deviation is required. The rotary vertical drilling system (RVDS), as it is known, basically uses borehole sensors to measure the borehole inclination and transmits the data to an electronic unit. If the pre-programmed directional limits are exceeded, the steering function is initiated by the hydraulic steering system, which extends or retracts four external, independently operated control ribs. These ribs generate radial forces and work against the angle build up.
When Modern Mining was in site in March, the reaming of the first shaft was underway and holing through was due just as we were going to press with this issue. Once the first shaft is complete, a mobile crane will be used to lift the HG330 (which weighs about 70 tonnes) and transfer it to the next shaft location. All three shafts are due for completion by July 2009.
Apart from Murray & Roberts Cementation, other companies involved with the Townlands Ore Replacement Project include RSV, which is the EPCM contractor, Bluhm Burton, which is responsible for the refrigeration plant at the ventilation shaft complex, and Norkim Construction and Mining, which is undertaking drop raising. There are just over 500 people working on the project.