Block Caving - A Cost-Effective Underground Mining Method
Block caving is a very efficient underground mining method. Its costs are lower than other mining methods per tonne mined. In addition, it requires a lower ventilation requirement. It also allows for a more flexible use of equipment, such as LHDs.
In block cave mining, a section of the rock mass is undercut and then collapses into excavations. These form ore extraction drawpoints.
Cost-effectiveness
Compared with other mining methods, block caving is one of the most cost-effective ways to mine copper and gold. It also reduces the need for surface waste disposal. However, it requires substantial planning and infrastructure and a long lead time. This method can be more sensitive to world events than other mining techniques, making it a riskier investment.
To develop a block cave, access shafts are excavated to a level below the ore body. Horizontal tunnels, known as haulage tunnels, are then dug benearth the ore body. These are followed by a series of upward-sloping tunnels, known as raises. Blasting is used to create these, and large rock funnels, called drawbells, are excavated beneath the undercut level.
A major challenge for block cave mining is the ability to fracture the rock mass and generate enough fragmentation to support long-life drawpoints and excavation tunnels. This requires preconditioning, which is a comprehensive process that includes destressing and fracturing the in situ rock mass.
Safety
Block caving is a safe mining method, but it requires special skills and equipment. Mining machinery manufacturers have been developing automated systems to increase safety. Caterpillar has developed a system for loading and hauling that is specifically designed for block caving, making it safer for miners.
This system will enable real-time mapping of cave material movement, which can help minimise dilution and improve recovery. It will also allow miners to design cave layouts that are more efficient. It will also help reduce mine safety risks and environmental impacts.
The technology has already been tested at Ridgeway Deeps and was found to be effective. It will be available on the market next year. Its development is supported by the mining industry and the University of Western Australia. Increasing numbers of PEAs and feasibility studies are recommending the use of this technique. This is a good sign that the future of block caving is bright. It can be used for both new mines and for extending the life of open pits.
Environmental impact
The success of block caving means mining companies are turning to it for deeper ore bodies that could not be mined profitably using traditional methods. However, deeper rocks are stronger and less fractured, so they require a lot more support to allow for natural caves to form. This means that companies need to give nature a helping hand, using technologies such as remote operation and collision avoidance systems for hydraulic breakers.
The development sequence for a block cave begins with the establishment of access drifts around the ore body. Once this is done, a grid of crosscuts are developed for workers and equipment. A new level is then developed above the first drift, and mining begins. Blasting and hydraulic breaking are used to break up the ore.
The key to successful block cave mining is a well-designed development, which allows for the creation of undercuts that will automatically collapse when the orebody is undercut. The dimensions of the undercuts are important, as they determine the speed at which ore is drawn down through the drawpoints and transferred to the transfer raises. Insufficient undercuts can lead to a loss of productivity and may cause the cave roof to stabilize or even collapse.
Technology
Increasingly, mining companies are considering block caving as an alternative to developing new mines or extending the life of existing open pits. The method involves drilling access shafts into an ore deposit and excavating a network of tunnels underneath the surface. These tunnels are known as haulage tunnels and are linked by upward-sloping rock funnels called raises. They are excavated by blasting from a central location called an undercut.
Block caving has several advantages over other underground mining methods. It offers higher production rates and lower operating costs. It also reduces the amount of waste rock generated by a mine, as it is buried below ground level.
However, the process requires significant initial investment and long lead times. It can take up to 20 years for a large-scale block cave to be established. Furthermore, the method is not suitable for all ore bodies. The rocks should be competent, with good permeability and low fracture energy.