Technology and innovation
Since 2010, the AngloGold Ashanti Technology & Innovation Consortium (ATIC), established by AngloGold Ashanti, has been looking for ways to leverage established technology in new ways, in an effort to not only extract additional gold from current depths of around 4,000m, but also to realise its long-term vision to reach depths of 5,000m and beyond.
In the current drill-and-blast paradigm used in deep-level South African gold and platinum hard rock mining, only drilling and cleaning is mechanical, while blasting makes use of explosives. This results in significant delays, as the mine has to be evacuated to blast and clear blast fumes. Additionally, blasting poses a significant seismicity risk, while the associated shift process does not allow for a continuous, 24-hour operation.
During 2013, the ATIC made good progress in prototype development pertaining to the key technologies that are aimed at establishing the base to safely mine the gold currently not in existing mine plans, such as that located in shaft and stability pillars, as well as at greater depth, at AngloGold Ashanti’s deep-level underground mining operations.
To address some of these challenges, reef boring has been identified as a potential solution. Raise boring in its current form is used as a vertical drilling technique for ventilation purposes and ore passes, boring mostly through waste rock to create the support services needed for mining operations. However, it was decided to investigate and test the feasibility of using raise bore machines to drill out the gold bearing reef. By applying existing technology initially, the raise bore machine proved successful in drilling out the reef, extracting only the gold-bearing rock or channel width, thus significantly reducing the amount of waste.
During 2013, the project saw significant progress in reef boring. During the last quarter, the technical viability of drilling adjacent single pass holes to ensure maximum orebody extraction was demonstrated.
To continue with our vision to mine “all the gold” the next holes will be drilled immediately adjacent to one another to verify the results obtained in the first test, after which the overlapping drilling configuration will be tested. Favourable results in the penetration rates of the drills along with speed and cuttings have also been achieved, with the average time taken to complete the last set of holes now at 3.5 days, from an initial nine days.
Another key area currently under investigation for the new mining paradigm is the development of an ultra-high strength backfill (UHSB) product and application system. This was identified as a key innovation required to enable mining at greater depths while also setting the platform for the drilling of the reef by means of reef borers. With the current method to stabilise pillars, an extraction percentage of approximately 60% is achieved. The newly-developed backfill product has been developed with a view to replacing the pillars, which will increase the extraction percentage.
During 2013, enhancements to the batch mixing process for the UHSB product progressed well, increasing mix volumes and reducing preparation time.
A replica of the underground production-site mixers was constructed on surface for testing to ensure operational readiness. Construction of an underground backfill plant began in December 2013 and is scheduled to coincide with the startup of the first production site in April 2014.
Stress monitoring instrumentation installed within the filled holes produced real time data, indicating that performance and effectiveness of the UHSB were satisfactory and showed that the UHSB minimised the effect of reef-boring extraction on the surrounding rock mass.
While this chosen paradigm provides ample potential for the business, the project also provides an opportunity to improve the skills of the current labour force in local communities. Work is also being done to address socio-economic and labour issues and to ensure that the local communities that host us will benefit from this development through secondary industries that are likely to emerge and operate at surface. In line with the Mine Health and Safety Act, this development is expected to assist with operational efficiency and also address safety challenges as we aim to optimise production output by introducing new mining methodologies alongside existing ones, as we incrementally introduce our new approach to currently sterilised ounces.