Mining Weekly

CARLETONVILLE (miningweekly.com) – South Africa’s Witwatersrand basin contains another 1.3-billion ounces of gold, almost as much gold as has been mined there since 1886 – but miners can only get to another 200-million ounces of it using today’s mining methods.

If the industry does not come up with a new way of mining, more than a trillion dollars worth of gold will not be mined, because the 1.1-billion ounces in question are either below the cutoff for the current mining method, or they are at depths where there are no technical solutions to get to mine those ounces.

Moreover, safety has reached a plateau and unless significant change is made to what creates this plateau, death and injury in mines will continue, which is totally unacceptable.

There is thus an absolute need to change – and senior VP technology and projects Shaun Newberry is at the forefront of an AngloGold Ashanti move that could result in all three billion Wits basin ounces being mined and not merely 1.9-billion of them.

Individual technologies currently under investigation will make a significant impact on the current mining method, where reverse circulation drilling will ensure enhanced information and better planning.

Reef boring and ultra high strength backfill will drastically reduce risk and technologies will also combine to allow AngloGold Ashanti to extract additional gold which was previously lost to the current mining method, Newberry told Mining Weekly Online in a one-on-one interview at the TauTona gold mine, where testing of new technology is under way.

The technology that AngloGold Ashanti is prototyping and which has already produced nearly 2 000 oz of gold is aimed at safely mining all of the gold, only the gold, all the time, without drilling and blasting.

The new mining method requires exponentially more geological information to deploy the proposed new method.

Rich shaft pillars, which cannot be safely mined using current mining methods, are being targeted as quick wins that will be mined and backfilled with ultra high strength backfill.

AngloGold Ashanti reported in its second-quarter presentation of results that its technology innovation consortium had made progress in prototype development for a safe, automated mining method intended for selective use at the company’s deep-level underground mining operations.

Site equipping, opening up and development of the test sites at the TauTona gold mine has been completed and work continues on equipping the test sites at the company’s Kopanang, Great Noligwa and Moab Khotsong gold mines.  

Nine holes with diameters ranging from 660 mm to 1 060 mm have been drilled at the TauTona test site at a rate of 4.5 days per hole and reaming bits used for wider reaming of five 150 mm pilot holes at the Great Noligwa gold mine are being modified to overcome problems.

TauTona’s underground backfill plant allows for a semi-automated process to prepare the ultra high strength backfill, which has successfully filled all available reef bored holes in the test site.

Testing at surface is continuing with the development of a pumping solution towards a 1 000 m horizontal distance target. 

The new technology is expected to significantly improve the efficiency of gold recovery during the mining process by removing the loss of fine gold in micro cracks developed in the rock as a result of blasting and the loss of gold in the transportation of product from the rockface to the mill.

Up to 40% of additional gold is lost by a combination of these factors.

Utilisation of assets is currently low because of the very nature of the drill, blast, support and cleaning method.

Mining also takes place on only 270 of the possible 365 days in a year and owing to technical constraints, only 66% of the time on those days is used for rock breaking and transport.

This can be thought of as only half of the time available in a year being used for productive mining.

These factors together are threatening the sustainability of gold mining in South Africa.