JOHANNESBURG (miningweekly.com) – The innovative Mark IV high-technology machine that AngloGold Ashanti is developing to improve the economics of gold mining in South Africa’s low-height, hard-rock reef is continuing to make progress, AngloGold COO South Africa Chris Sheppard said on Monday.

Speaking at Monday’s presentation of half-year results, Sheppard said in response to Mining Weekly Online that the machine was continuing to show pleasing progress ahead of its ultimate design still having to be determined.

“Overall, it’s looking pleasing,” he said.

The latest-generation Mark IV reef-boring machine is being put through its paces at the TauTona gold mine’s lower carbon leader shaft pillar and other machines have also been deployed at the Savuka gold mine carbon leader shaft pillar project, which Sheppard describes as “early days at this point in time”. (Also watch attached Creamer Media video).

Setting out technology in its half-year presentation document as a top-five priority, AngloGold revealed that talks are under way with the Department of Mineral Resources for permission to conduct continuous, round-the-clock operations, which will significantly strengthen the business case for the fuller introduction of its new raise-boring technology, which dispenses with conventional drilling and blasting.

Mining 365 days a year instead of the current 260, which the blast-free technology allows, provides the necessary time to complete the number of holes each machine drills a month.

“We’re busy with a whole suite of research and development, and following quite a rigorous programme of stage-gating, to make sure we’re spending our money in the right areas and getting out proverbial bang for our buck,” Sheppard told Mining Weekly Online.

Sheppard described as “interesting” global construction and mining equipment manufacturer Caterpillar’s launch of the first continuous mining and hauling system for underground hard rock applications, which is designed to replace conventional drill-and-blast operations in low-height environments, ranging from 1.3 m to 2 m, as well as in bedded deposits such as certain types of platinum, copper and gold deposits.

At last count, cycle times at TauTona were moving closer to the targeted 72-hour blueprint.

Ultrahigh-strength backfill product has also been developed to be able to pump over the required 1 000 m distance, a prerequisite for a full production mining cycle.

The new raise-boring technology produced 100 kg of gold for AngloGold Ashanti in 2014 and was targeted to be competitive with conventional mining in 2015.

The company has used the raise-bore technology to drill in shaft pillars that are unsafe to mine conventionally.

So far, the technology has put the company in a position to mine “all the gold and only the gold all the time” and to overcome the current drill-and-blast constraint of only being able to work 66% of each day.

This resulted in discussion being opened with the union at TauTona to embark on a programme of continuous mining.

The need for the new technology is compelling, as only 60% of the gold ore in South Africa’s rich Witwatersrand basin is accessible using current drill-and-blast technology and 40% of the gold is left behind in pillars to keep seismicity at bay.

The current mining method then loses a further 25% to 30% of that 60% because blasting breaks the ore into so many pieces that not all of them can be recovered, particularly as fractured sizes range from fine powder to large boulders.

Once blasted, the product is moved up to seven times, which results in more losses.

On average, there is 200% more waste than gold in the mix moved and dilution can be as high as 1 500%, which means that huge volumes of nonpay material have to be transported out of ever-deepening cavities.

One hundred grams of gold in the ground becomes 30 g or 25 g of gold on surface, after getting out only 60% of what was there in the first place.

What is far worse is the death and injury rate, which remains in spite of the huge effort to achieve zero fatalities.

During the twentieth century alone, the Leon Commission calculated that 69 000 people were killed in South Africa’s mines and a million seriously injured, maimed or physically damaged.

Currently, safety remains volatile and, unless significant change is made, death and injury in mines will continue.

There is, thus, an absolute need to change if deep-level gold mining is to be sustainable – and AngloGold Ashanti has been a prime mover in this under senior VP: technology and projects Shaun Newberry.

The current mining method is clearly not the one that should take South Africa into the future.

In fact, if it continues to be pursued, gold mining will end long before the Witwatersrand basin’s three-billion ounces of gold are extracted.

Some 1.7-billion ounces have been mined, only 200-million more ounces are in reserve and 1.1-billion ounces stand to be left in the ground unless a new mining technology is introduced.

Since 2010, AngloGold Ashanti has been working consistently to introduce a safer and more efficient way of mining narrow-reef orebodies and has developed and manufactured prototypes in a relatively short time.

The new technology involves boring holes of the required reef-channel width, collecting and transferring the bored chips in an enclosed system for further processing and backfilling the cavities to stabilise the underground environment and reduce seismicity.

In order to reach depths of 5 km and beyond, the rock mass removed needs to be replaced with similar material of 170 MPa compressive strength to prevent movement.

Each hole is sealed at the bottom access point and a high-viscosity mixed product is pumped to the top access point.

All this is already happening. Steps are being taken to enable the reef-boring machines already in use to move and align themselves automatically on the basis of geological data.

Near-term work is also being undertaken to evolve towards a form of gold liberation using chemicals, thermal energy or other methods, to free the gold for hydraulic transport back to surface and achieve the original vision of having gold on tap 24 hours a day, 365 days a year.

Knowledge of rock fragmentation is also an enabler for reef boring, as less power will be needed if better rock fragmentation methodology can be developed.

There are many such projects under way in the background because of their relationship with the programme’s first two stages.

But exponentially faster geological information will be needed to deploy the new technology.

To be able to bore the reef over distance, the location of the gold-bearing rock will have to be determined far more quickly and accurately.

Currently, there is nothing available that can provide the information at the pace needed and something suitable will have to be developed. In the meantime, the quick win of shaft pillar mining is being seized upon, where such information is already available.

High-speed haulage-boring machines are needed to create the main infrastructure for logistics and geological drilling platforms as well as smaller-diameter access for on-reef infrastructure.

Once the on-reef grid has been established, the idea is for ventilation to be achieved by drilling holes between the drives using a raise-bore machine.

It is envisaged that reef boring and ultrahigh-strength backfilling can then take place from the drives.

Reef-boring begins from the bottom reef drive using a machine set up on the lower of the two levels to be connected.

Line boring is used to drill a hole from the lower level to the upper level and is then backfilled on completion.

The completed hole has smooth walls and does not require support.

The vision is of mechanical mining being remotely controlled from safe areas, extraction ratios being boosted by a new mining methodology, and backfilling of cavities with material as hard as the rock itself.

Targeted are significant portions of orebody currently left behind and the elimination of gold loss down microcracks.

Instead, the plan is to transport consistent smaller chips from the rock face to the mill in one enclosed system. The technology is said to have the potential to increase the extraction ratio from the current 60% to 70% to at least 80% to 90% and will help solve the high closure challenge expected at mining depths of 5 000 m and beyond.

Skin-to-skin drilling leaves a wedge of gold that may be recovered by lancing or micro-waving. The second stage is targeting intelligent mining machines and the third stage a visionary gold-on-tap mimicking of the oil and gas industry.

The three cohesive stages of the roadmap aim to bring sustainability to gold mining at ever-increasing depth, with safety, extraction ratio, dilution, mine call factor and asset use coming under the microscope.

If the country succeeds in finding a viable new alternative, it would not only be able to mine all remaining pillars and go to the ultradepths, but it could also reopen a large number of closed mine shafts and revive mining ghost towns, which is why the national shoulder needs to be put to the wheel with the utmost vigour.