The expert, who leads the Deep Mining Geoscience research group, pointed out that cave mining will be critical to the future of the mining industry as surface orebodies become rarer, discoveries at depth more common, and the energy transition increases global demand for minerals.
“In the past, we have considered various geotechnical risks when mining underground, but as we begin mining at depths beyond 1000 metres there are going to be geotechnical and operational risks that trump the traditional suite of geotechnical hazards,” van As, who was Rio Tinto’s general manager for geotechnical engineering & cave management for eight years, said. “The deeper we go, the less forgiving geotechnical hazards are, and companies and stakeholders need to realize that the consequences of not identifying and managing these in design and operational strategies could effectively lead to significant mine underperformance or even premature closure.”
Stress-driven hazards
In his view, the increased exposure of mine personnel to stress-driven hazards, such as rock bursts, cannot be understated and warrants every effort and strategy to be adopted to manage and minimize such risks.
“At those depths, there are very few levers to pull if something goes wrong – for example, if you’ve invested 10 billion dollars to build a large, deep cave mine, which could take 5 -10 years, and things go wrong during undercutting or production ramp up, you could lose 10 billion dollars before you have even mined a tonne of ore,” van As noted.
The researcher said that there are numerous design parameters and strategies that are unique to operating at depth which need to be thoroughly studied before they can be reliably incorporated into the design and execution.
“For example, in cave mines, one of the greatest overarching risks is the stability of the production level – the level where all material is extracted through tunnels and draw points – because if we can’t keep those tunnels open then we can’t produce ore,” he explained. “There could be hundreds of thousands of tonnes of material passing through every single drawpoint on the production level and so we need to adopt every tactic at our disposal to try and preserve the condition of the rock in order to maintain the integrity of the level for the duration of its life.”
For van As, preserving the condition of the rock may mean excavating better and adopting methods that induce less rock damage. Implementing such methods likely takes longer and, contrary to what normally happens, the extended time should be factored into the development and construction schedule.
“This demonstrates the tension between two competing design objectives – trying to bring the mine into production as fast as possible and trying to ensure the long-term operability and performance of the mine,” he pointed out. “If there is premature production level closure and you can’t mine anymore, then any costs saved by getting into production sooner won’t matter.”
