The Holy Grail of Caving: Rio Tinto Embracing Cutting-Edge Technology
This article was originally published in Rio Tinto's M2M Magazine and is re-published here with permission. The article is written by Lita Madlang, Communications Specialist at Rio Tinto.
In 1666, a 24-year-old Isaac Newton famously watched an apple fall from a tree in his garden, giving him the inspiration for one of science’s great discoveries – the law of gravity. Newton’s breakthrough led him to decipher some of the secrets the universe then held, such as what kept the planets in orbit around the Sun. Today, an understanding of the way rocks flow under the force of gravity is essential to developing underground cave mining methods that are both safer and more productive. Rio Tinto is harnessing this fundamental scientific principle to drive the development of cutting-edge technology.
Rio Tinto has partnered with CRC Mining and technology supplier Elexon Mining to develop a cave monitoring system that will increase the safety and profitability of underground mining operations. Dubbed “Cave Tracker”, the system is designed to help measure the movement of fragmented rock under gravity and manage its flow through controlled extraction.
Andre Van As, general manager, Geotechnical Engineering & Cave Management in Rio Tinto’s Copper & Coal group, said the technology addressed a key challenge of underground cave mining. “While we have previously been able to monitor the area surrounding the cave closely, very little has been known about the movement of the rock inside the cave itself,” said Andre.
“We have been able to place markers in drill holes within the cave and measure where and when they come out on the extraction level, but we have not been able to measure what happens in between. “This lack of real-time information has commonly led to part of the orebody being left behind or diluted.”
The Cave Tracker system uses a series of trackers and detectors placed in and around the orebody to track the rock three-dimensionally inside the cave as it moves in real time. The system can transmit signals through two hundred metres of rock and will continue working remotely for many years, even as it is impacted by the rock deep underground.
“We can only manage what we can monitor, and with Cave Tracker, we can now see into the cave and monitor the mass flow of caved rock,” Andre said. “That means we can make better decisions to manage the flow of ore and waste, improving our profitability. In large-scale underground operations, even a ten per cent reduction in waste can represent hundreds of millions of dollars of value. The ability to monitor the flow of rock within the cave truly is the holy grail of caving.” (Article continues below image.)
The driving force
Underground cave mining, also known as “block caving”, involves blasting and removing a large area of rock far beneath the surface to create an underground void that causes the rock mass above to break under gravity. This eventually forms a cavern of fragmented rock which is then removed from an underlying extraction level.
After the initial blasting, the use of the natural stresses and gravity to break the rock – rather than explosives -- allows large underground orebodies to be mined more cost-effectively than other underground mining methods done on a large scale.
Image: The orebody being prepared for blasting, Oyu Tolgoi, Mongolia.
In addition to delivering significant productivity improvements, the technology also has the potential to make cave mining safer. In some cases, large voids can develop within the cave, and if a large enough air gap collapses, air can be pushed through the mine with incredible force. The Cave Tracker system, in conjunction with other cave monitoring systems, can be used to detect the formation of air gaps and manage them before they pose a safety threat.
“This technology is a breakthrough that was nearly a decade in the making,” said Craig Stegman, chief Growth & Innovation officer in the Copper & Coal business. “Perseverance and collaboration is revolutionising underground mining and unlocking significant value.”
Following a proof of concept led by Rio Tinto and CRC Mining at Northparkes Mine in 2007, the journey to design, develop and perfect the technology has culminated in a full-scale trial at Argyle's underground diamond mine in Australia that began at the end of 2014. Once testing is successfully completed, Cave Tracker will be deployed at Rio Tinto's Oyu Tolgoi Underground Project in Mongolia.
How Cave Tracker works
While most signals won’t travel through rock, slight changes in magnetic fields can be detected with sensitive equipment. The trackers, invented by CRC Mining chief executive officer Paul Lever and his team, use battery-powered spinning magnets that send signals through rock. As the trackers need to work underground for many years, the team had to optimise the battery life by making the magnets spin as efficiently as possible.
A key challenge was to create a device small enough to be placed in drill holes, yet powerful enough to capture and transmit a huge amount of data. It also needed to withstand the immense force of rock, so the team brought in a NASA engineer to assist in designing a tough outer shell to protect the trackers deep underground.