Once the Mechanical Rock Breaking Technical Design Study, currently at early feasibility study stage, achieves its intended outcome of a fit-for-purpose mechanical cutting product, it will allow miners to unlock significant tonnages from narrow reef hard rock mines in the platinum group metals (PGMs), chrome and gold sectors, says Mandela Mining Precinct’s (MMP) Martin Pretorius, Programme Manager: Longevity of Current Mining (LoCM) and Mechanised Mining Systems.
ROBINS Mine Development Machine, Innovation in tunnelling, What we learn from novel tunnel boring machines, B Grothen SANCOT 2022.
Adapted mechanical cutting equipment, such as tunnel boring equipment, for underground narrow reef hard rock (NRHR) mining will be a game-changer, enabling miners to mine more precious resources efficiently, while simultaneously removing workers from hazardous working areas.
“PGM and gold mining reserves are steadily depleting and timeous replacement of shaft infrastructure to replenish resources is a concern. Advancing mechanical cutting technology initiatives for the industry will be a boon. To date, efforts in applying mechanical cutting equipment in the NRHR environment have not been successful, largely because mining houses have been using existing equipment that has not been modified to the niche market application. As a result, it is imperative that industry players undertake pre-study work to design and manufacture equipment that is specific to the application.”
Although mechanical cutting has not proved to be effective locally, internationally tunnel-boring technology has been extremely successful and is being used extensively for underground tunnelling.
Locally, NRHR mines are currently being mined using the drill and blast method – a labour-intensive high-risk, cyclical slow process, which is why the Mandela Mining Precinct (MMP) and its partners are engaged in a Mechanical Rock Breaking Technical Design Study, which is investigating options to develop mechanical cutting equipment for local narrow reef operations.
According to Pretorius, modified tunnel boring machines used in the development of underground transport, including the Gautrain, could be extremely effective in NRHR mining.
“In seeking to become more efficient, local mining houses have trialled mining equipment from local product manufacturers and international suppliers. Leading mining house Rio Tinto recently used a raise-boring machine to sink a shaft – a move away from the conventional method of shaft-sinking – and it proved to be successful. A diversified miner has also been testing tunnel boring equipment to develop a decline shaft in the Limpopo region; however, the miner encountered challenges in the process. These examples illustrate that local mining houses are keen to test equipment that unlocks benefits, and it is important to note that the equipment trialled to date has been manufactured equipment that is not designed for NRHR application.”
Pretorius adds that one of the key challenges associated with testing equipment supplied by international equipment manufacturers is that a huge block of the Merensky reef or UG2 reef has to be shipped to the supplier’s headquarters, which could be in Germany, for testing.
“Such an initiative comes at a massive cost, and a prolonged timeframe until miners can get the required results. The advantage of the Mechanical Rock Breaking Technical Design Study project is that it allows collaborative design and development of a product that is suitable for local conditions, and which would enable testing of the product at the MMP test mine within the hard-rock environment. As it is, we have collaborative capability, resources, and a suitable test facility that will allow modification of the machine during its development and testing stages for the NRHR environment.”
Need for speed
A key advantage of mechanical cutting equipment is that it offers speed and efficiency, and thereby increased productivity.
The traditional drill and blast method is bound by construction work and is undertaken a few times a month, which allows for the development of between only 100 m to 200 m per month. In contrast, a tunnel boring machine, for instance, would be able to achieve significantly improved results – as much as 600 metres per month – almost three to four times what is currently achieved.
“If mining is to continue in areas such as Rustenburg, where it takes place between 800 m and 2 000 m underground, and where the upper areas are about to be mined out, more shafts will need to be sunk. Having a piece of equipment, such as the tunnel-borer, that can rapidly develop an underground connecting highway infrastructure will significantly lower the capital costs of progressing mining in the deeper, lower areas. Furthermore, given that the Rustenburg area is home to several mines, mining houses could potentially co-fund a machine modified for their local conditions, which would deliver significant advantage to the regional players. Such a machine would allow miners to access connecting points to multiple shafts and resources, which would become the starting point for next generation shafts – these could be interlinked using raise-boring equipment.”
However, given that tunnel-boring machines are developed for single use application, after which the multi-million-rand machine is discarded, Pretorius believes that opportunity exists to modify a tunnel-boring machine for extended use. Such a machine would be used to tunnel from a centre point out, connecting mines that are contiguous.
Importantly, high-speed tunnelling is becoming a critical requirement to access replacement resources timeously.
The strong demand for metals, particularly PGMs which have gained traction on the back of demand for clean energy sources, remains an impetus for introducing mechanical cutting equipment. Further to this, such equipment will reduce the number of people at the rock face, allowing them to operate within lower risk margins of semi-autonomous equipment.
“The Mechanical Rock Breaking Technical Design Study project is aligned to the Mechanised Mining Systems (MMS) programme strategy, which aims to optimise mechanised mining practices that will allow for high-speed tunnelling at NRHR mines. There is a future strategic intent to develop atomised automated mining solutions for NRHR gold, chrome, and platinum mines. This project aims to find solutions for effective application of mechanical cutting equipment with advanced technological systems to replace drill and blast practices. High-speed mechanical cutting equipment will be able to open up more ore reserves rapidly. This collaborative approach, which includes industry representatives, R&D collaborators and manufacturers, will make a positive contribution to the project outcome,” explains Pretorius.
Mechanical Rock Breaking Technical Design Study project
In its latest endeavour to design and develop mechanical cutting technology, the MMP has partnered with major international equipment specialists Herrenknecht, an expert in tunnel boring machines, and Robbins, which designs and manufactures raise-boring equipment.
Initiated in (2020), the project study comprises two phases, the geotechnical design and the mechanical design, with the geotechnical study (Phase 1) covering the basic mechanisms of mechanical rock cutting, the geological setting, and an understanding of key geotechnical parameters and information requirements, which are critical for any mechanical rock cutting design (Phase 2).
“As a starting point we needed to understand what mechanical cutters can achieve, the related implications of implementation, which aspects of local applications have been successful and which have failed, and why. We also explored aspects related to the exact dynamics of the mechanical cutting machine, how it can be applied, how far advanced international equipment producers are in relation to our needs and the parameters of possibility of the mechanical cutting machine, ie, its use in various applications and how far at depth we can use the equipment, given that South African gold mines, going to a depth of 4 km below surface, are some of the deepest mines in the world. What we subsequently discovered is that it is not only related to mining design as a function but extends to the civil engineering function. We also concluded that the project will have to be undertaken in two stages: Phase 1, which will include the geotechnical design, followed by Phase 2, which will include the mechanical design,” explains Pretorius.
To date, the MMP and its partners have identified all the critical parameters required and have established the study framework, which outlines the steps needed to meet its objectives.
“We have completed the early work needed to understand the parameters of the project and this year have undertaken a technical study aimed at reaching out to the mining industry for information related to the parameters that will allow us to establish a database to determine a suitable initial design.”
Within the geotechnical design phase, the following have been established:
q mechanical cutting equipment types and applications;
q an understanding of mechanical cutting design requirements;
q identification of the geotechnical parameters;
q a study framework to guide further study work.
According to Pretorius, the project is progressing into the second phase of the geotechnical design, which entails obtaining relevant geotechnical information.
The MMP has been collaborating with the mining industry and tertiary institutions over the past three years, and has established a technical steering committee to guide the programme.
“So far, we have good representation from the mining industry, the manufacturing sector and universities, and excellent information sharing taking place. We also have key, influential personnel in the geological space at the MMP’s Advanced Orebody Knowledge (AOK) for in-depth knowledge of the orebodies and rock engineering. Given that some of the information required is beyond the normal mining practice domain, we had to look to the civil engineering segment for assistance and have been relying on the Civil Engineering Department of the University of Pretoria.”
Further to this, the MMP has also been collaborating with industry heavy-weights Anglo American, and precious metals producer, Sibanye-Stillwater, who are supplying information from their case-studies on equipment trialled at their operations.
“The more resources we can muster, such as related high-level skills sets and financial assistance, the quicker will be the timeframe to progress the studies and get into product design and development. As such, we have included as many people and equipment experts in the project as possible. The greater the buy-in from industry and key-stakeholders, the greater the appetite and the resources to fund the project. From then it’s a shorter time-frame to product commercialisation,” explains Pretorius.
“Herrenknecht and Robbins participated in the process to develop the framework for the study, which included geotechnical assessments and identifying the required parameters. They shared their learnings from their case-studies and their expertise in the field.”
Opportunity to unlock new reserves
While South Africa is blessed with vast quantities of PGM reserves (roughly 80% of the world’s reserves), Pretorius notes that on the back of the voracious appetite for the commodity, which is driven by the need for clean energy sources, current reserves are fast depleting without replacement infrastructure.
According to SFA Oxford (2021), South Africa is a major supplier of the PGMs, namely platinum (74% of world supply), palladium (39%), rhodium (82%), iridium (81%), and ruthenium (90%).
“There is a significant demand for platinum now and in the long-term. Raising capital to sink shafts is costly and, while demand for PGMs is strong and the price is rising, it is an opportune time to develop advanced equipment. If we don’t replace resources fast enough, we will have a gap in maintaining our production ounces. A key way to speed up the process is to implement tunnelling that will connect some of the shafts and significantly reduce the time of ore replacement.”
Time-line to new technology
The MMP is looking to complete Phase 1 of the project – the geotechnical study portion of the initiative – by March 2024 followed by Phase 2, the mechanical design component, which is expected to take roughly two-years. By 2027, the MMP and its partners expect to be in the final stages of developing a mini-prototype and undertaking underground testing at the test mine.
Although the project is currently being funded by the Department of Science and Innovation, Pretorius says that owing to the high cost of the project, Phase 2, will require partners to co-fund the process and the design process.
“This is a high-cost initiative and therefore extremely dependent on co-funding. Just to get to the point of designing and trialling equipment at pilot scale will easily exceed R100 million. During Phase 2, we will rely heavily on external funding from mining houses, stakeholders and interested parties.”
With South Africa being a leader in deep-level mining, the development of a mechanical cutting prototype will be a game-changer for the local mining industry as it will unlock significantly more reserves and thereby lift miners’ profitability. Moreover, as mining is a key contributor to South Africa’s GDP, the export of more minerals would mean an improved balance-sheet for the country.
“Although most mines internationally are shallow operations, the commercialisation of a mechanical cutting machine will see South Africa as a technology leader for mining at depth,” concludes Pretorius.
