AngloGold has forced itself to think differently about deep level mining and this, they are hoping, will spawn an operating section employing the new technology by end 2013.
JOHANNESBURG (Mineweb) – When Apple launched the iPad, it didn’t just alter the numbers spinning about on its profit line, it changed the technology industry.
And if AngloGold Ashanti executive vice president of business strategy, Canadian engineer, Mike MacFarlane is to be believed the gold digger is looking to do something similar to deep level gold mining.
Since 2010, the group has been looking for ways to leverage old technology in new ways to mine gold even deeper than the current depths around 4kms. And, it is now aiming to introduce a new operating section at AngloGold by the end of 2013 that moves away from the conventional drill and blast methodology to one where the ore bearing reef is extracted with modified raise bore drills.
The raise bore drill, called an Amtek, is currently undergoing testing and is sourced locally in South Africa from a company called Atlantis. It is commonly used for the vertical drilling of ventilation shafts or drain and service holes and has been adapted for the horizontal drilling application.
Besides the safety and productivity advantages achieved by eliminating the need to blast, this could have the potential to allow the gold digger to reach the illusive 5km depth mark at its mines.
MacFarlane says, “It is a little bit like the invention of an iPad, you just never go back….the days of drilling and blasting are over, it’s going to take a while, but drilling and blasting is going to come to an end”.
Advancements like these are long overdue. Call me naïve but after having visited a few coal mines and being accustomed to the mechanisation in the soft rock environment (admittedly at much shallower depths!), my first trip to a conventional section at a gold mine left me with the feeling that I had been thrust back in a time machine.
AngloGold CEO Mark Cutifani confirmed that related work on this type of mechanisation was already being looked at in the 1970s but the challenges with finding a suitable backfill material to fill the voids left behind halted the progress. Developments over time in cemented hydraulic backfill material have changed this scenario.
“We’ve now developed back fill that has a strength of up to 250 megapascals (MPa) and for those that remember backfill thirty odd years ago that is a massive number. It’s expensive but more importantly instead of being 30% compressible it is about 5% to 6% compressible” said Cutifani.
To put this into perspective, a bag of general purpose cement like Surebuild from PPC has a standard strength of between 42.5 and 62.5 MPa after 28 days.
Work is being done now on finding the optimal mix between cost, compressibility and strength so that there is a viable alternative to filling the holes left behind said the CEO.
Showing a short clip of the drill at work at the company’s interim results presentation in Johannesburg, Cutifani explained that the first 30 metre long hole that was drilled into the reef structures at its almost 4km deep TauTona mine took six weeks.
The six weeks were used to develop an 8 inch pilot hole and then accurately set a 1.2 metre reamed (widened) hole around the pilot hole said the CEO.
The step change is already evident in that a second hole was completed in nine days. The aim is to shorten this time until it can be achieved in one day.
The miner is currently drilling its third hole and, if 30 metres of ore are recovered, this equates to approximately 28 to 30 ounces of gold per hole said Cutifani.
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