Deep ore mining goes cutting edge
A new type of drilling system for sinking shafts could mean that many underground bodies of ore that were previously too expensive or risky to get to can now be mined.
In the next two years, Master Drilling, the mining innovator with its giant drilling machines, will build a device that can sink a 2km deep mine shaft twice as fast as using explosives could.
It will also be about a third cheaper than the explosives, which were for more than a century the only affordable and reliable way to sink underground shafts.
It is also considerably safer and a lot less harmful to the environment.
Master Drilling, which develops its world-renowned technology in dusty Fochville, Gauteng, has designed the system and is now calling for tenders for its construction.
Louis Germishuys, chief operating officer of shaft development at Master Drilling, said: “We expect to be ready to sink the first shaft with the system in 2018. We must find the right customer for it.”
The new drilling system, which is known as the blind shaft boring system, is a combination of three proven systems developed by the company: a pilot drill that drills an initial narrow shaft, a raising bore that widens the shaft and a hoisting system that removes material from the shaft.
The system sinks a shaft at a rate of 7m a day. In shafts sunk with explosives, progress is no more than 3m a day.
According to a financial model, a 2km deep shaft costs about R9.4 billion to sink and takes at least three years to build, but with the blind shaft boring system, the shaft will be sunk within 18 months, bringing a saving of R2.8 billion.
It will cost between R400 million and R800 million to build the system.
It is operated by four to six workers. For maintenance, about eight workers are required.
For the conventional The pilot drill is a conventional drill with a diameter of 4.8m, which drills a pilot shaft. It uses a sludge-water technique where the boring head is under water and grinds the rock into sludge.
The drill shaft is hollow and the sludge is pumped up through it to a filter plant above the boring head, where the water and the crushed rock are separated.
The water is returned to the boring head, but the crushed rock is hoisted out of the shaft.
About 20m above the boring head is a reaming head that reams the pilot shaft wider in a dry condition with the same technique that large drilling contractors have for a long time used to widen pilot holes in rock.
The reamer is attached to a raised borer anchored downward and is moved by hydraulic arms fixed in the narrower pilot shaft.
The reamer widens the 4.8m pilot shaft so that the diameter of the final shaft can be between 10m and 14m wide.
That’s wide enough for any mining activity, from ventilation to transporting people, machines and ore.
The waste rock the reamer bores from the shaft walls is caught in a bunker and transported out of the shaft.
The system weighs about 1 500 tons and is suspended into the shaft by a sturdy hoisting system above ground. explosives method, about 40 workers are used to drill holes for the explosives and hoist loose rock from the shaft.
In addition, conventional shaft sinking is the most dangerous work in an underground mine.
“Yes, it provides less jobs, but when you consider how many mines could so far not be opened because it was unaffordable and will now perhaps in fact be opened, the technology does create jobs,” Germishuys said.
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