Mining solutions provider United Mining Services (UMS) is assisting with shaft refurbishment at a manganese mine, in the Northern Cape.
UMS COO Murray Macnab says the mine operators decided to extend the life-of-mine by refurbishing the old existing shafts and installing new shaft towers.The old shaft is being upgraded with new bunton and divider steel ends and new pipes in the shaft.
He explains that shaft refurbishment mostly entails replacing old rusted and damaged steel with new steel sections. It also entails realigning the steel to reduce wear and tear of the shaft steel and the conveyances, and reduces noise pollution by removing the slamming noise in the shaft.
Refurbishment takes place in-between shifts and off shifts to accommodate the mines production requirements, he adds.
“We started working on the shaft at the beginning of last year and we expect to complete the project by September.”
He explains that, as UMS has had to work during periods when the mine is not operational – after hours, and on weekends and during holidays – this has delayed the project.
UMS will also sink a new utility shaft in New Mexico, in the US, in a joint venture (JV) with a US-based business. This will start in June and, once completed in 2022, the final shaft will measure 8 m in diameter and extend to 693 m below the surface.
The JV is 50:50 with all-American general contracting company Harrison Western.
“Harrison Western has sunk shafts in the past but has not done so for more than 20 years. UMS brings the design and shaft sinking methodology along with the specification and procurement ofall sinking related capital equipment.”
Macnab notes that Harrison Western brings to the JV local expertise and 50% of the financing for the project.
Additionally, UMS subsidiary mining service provider Africa Mining & Engineering Technical Services has secured the design work for a new project in Botswana. Work has started and will continue for the majority of the year. The intention is to progress the project to procurement and construction over the next few months.
UMS services the mining and minerals industries by offering turnkey solutions for the entire minerals processing value chain, from concept studies to mine and process plant design, construction, commissioning, ramp-up and operation.
A further primary offering of UMS’s underground mining services is shaft pillar extraction.
In the case of the Evander Mine, although the shaft pillar extraction is done by the mine itself, Macnab notes that UMS is installing the shaft tower and pipe compensators and new pipe columns. This is done while the shaft is operational and so in many respects, it is similar to the managese mine upgrade, in that it is done in the off-shift periods and in-between shifts.
Shaft pillar extraction is the removal of the ore adjacent to the shaft that was left behind during miningto provide stability to the shaft structure by way of providing a solid pillar around the shaft.
When it comes to extracting the pillar, it requires a great deal of planning and rock mechanics analysis to design a methodology that allows extraction to be done safely, he elaborates.
In the process, the ground around the shaft will subside and the shaft barrel will become shorter and usually displaces in the direction of the ore gradient.
To compensate for this movement a certain amount of steel is replaced in the shaft and new steel is installed in the form of a compensating tower. The tower facilitates safe travelling through the shaft pillar zone by the various conveyances and rock skips.
Meanwhile, shaft work is carried out by a team of people with years of experience in working in a shaft where the bottom is more than a 1 000 m below them.
He adds that there are not many people who do this type of work and it requires “rare skills and passion”.
Additionally, before extracting the shaft pillar, several factors need to be considered, such as the depth of the pillar, the size of the extraction, geotechnical information and the stressors that might compromise the integrity of the shaft.
Macnab explains that when these factors are not taken into consideration when planning to extract and/or refurbish the shaft, it can result in serious implications, including loss of life and uncontrolled rock bursts.
Since some of the mineral resources around the shaft cannot be mined, miners choose to place shafts in the area with the highest ore content. This allows for the quickest return on investment, which starts as soon as the mining process begins, rather than waiting until the end of the mine’s life, explains Macnab.
He adds that shaft pillar extraction has only become relatively prevalent in the past 50 years and that, historically, most mining operations left the shaft pillars, and the ore contained within and around them, intact when the shaft and/or mine closed.
However, the push to maximise productivity and revenues has resulted in miners increasingly removing shaft pillars where possible, with some companies even attempting to reopen old shafts to extract the shaft pillars and mine the remaining ore.
“In terms of safe pillar extraction, mines should use mechanised mining methods and geotechnical results to understand the site, as well as implement the latest support methodology,” concludes Macnab.