Deep-level mining is becoming more common as a result of innovative technology, says design and consulting professional services company Stantec.
Stantec US and international mining VP Sandy Watson says deep-drilling technology for greenfield projects has continually been advanced, enabling mining companies to identify mineralisation at much greater depths with a reasonable level of confidence.
He tells Mining Weekly that deeper mining is also becoming more common in existing mines, owing to the depletion of orebodies closer to the surface.
“Current data suggests that 70% of existing mines worldwide are currently openpit operations, while 30% are underground operations. There is a likelihood that, by 2018, this ratio will be 50:50, with the trend moving towards more underground mining.”
Watson adds that advancing technologies associated with deep-mine hoisting, ventilation, refrigeration and ground support enable companies to mine safely and economically at depth, with the economics generally based on the value of the ore.
“The value of the ore must overcome the higher capital and operating costs of mining at depth, regardless of the commodity type,” he explains, adding that the mining methods used to economically extract the resource will vary, however, as they are determined by the size, shape, formation and geotechnical characteristics of the deposit.
Deep-level mining requires significant capital investment in mine infrastructure to allow for processes such as creating access to and ventilation for deep shafts, some of which are “as deep as 3 500 m or more”.
At these depths, hoist rope technology and rope strength become a concern, particularly when considering large production requirements and the associated skip payloads, Watson says, adding that dealing with increasing heat at depth also becomes a significant challenge.
To maintain reasonable working temperatures that ensure the safety of workers underground, refrigeration and cooling plants must be used.
“These ventilation and refrigeration requirements, and the associated power loads, become a significant capital and operating cost for deep-mining operations,” he states.
Watson explains that, in addition to transporting personnel, supplies and consumables from surface to underground, as well as hoisting ore and waste rock, shafts are also used for ventilation to maintain safe working conditions.
Other ways of managing the impact of heat on deep-level mineworkers include shorter shifts and more frequent rests in a temperature-controlled environment.
Further, owing to the higher heat loads generated at depth, the groundwater inflow temperature increases, presenting challenges in terms of personnel safety, equipment operability and maintenance.
He states that, as mining deepens, the increasing stress levels in the rock result in reduced excavation sizes and increased ground-support requirements to mitigate the increasing ground pressures and the risks of potential rock bursts.
“Additionally, the potential of fault activation may trigger a large seismic event,” Watson says, adding that seismic monitoring systems are becoming more important in deep-level mining because they provide better insight into rock mass response to excavation at depth.
He says, in shallower mines, there is greater concern with gravity failure, as the ground support needs to handle dead weight in static conditions. “For deeper mines, the support system must be able to handle changing conditions and yield to dissipate energy associated with rockbursts, and control large rock deformation.”
Watson says incorporating automation in deep-level mines is desirable as it reduces the number of workers exposed to, for example, higher temperatures and higher ground stresses.
Automation provides operational efficiency and productivity improvements that reduce overall mine operating costs and it could result in rendering a deep-mining operation economically viable.
Watson says some mines are using electric equipment such as load haul dump (LHD) trucks at depth to reduce the heat generated underground.
He adds that more mining companies are undertaking green technology trials.
Watson tells Mining Weekly that future deep-level mining will be characterised by increased automation processes and continued research into using robotics.
He says robotic technology, powered by artificial intelligence, continues to be developed and applied to tasks such as production and development drilling and blasting, and LHD truck loading and hauling, as well as ground-support installation.
Additionally, the continued development of electrically powered mobile equipment reduces the total ventilation and refrigeration requirements for deep underground mining. These ventilation reductions ultimately translate into less vertical development to sustain safe mining operations, subsequently resulting in reduced capital infrastructure costs, Watson explains.
Stantec has worked in deep-level mine projects at, for example, gold major Gold Fields’ South Deep mine, in Gauteng, South Africa; diversified major Glencore’s Kidd Creek mine, in Ontario, Canada; gold miner Homestake Gold’s Homestake mine, in South Dakota, in the US; and copper and gold mining company Oyu Tolgoi’s Oyu Tolgoi mine, in Mongolia.