Cave mining techniques are the most popular methods for exploiting massive orebodies deep within the earth.
In general, cave mining refers to all underground mining techniques in which the orebody is ‘undercut’ or drilled beneath the surface and is recovered as it falls. The removal of the ore causes a large gap or ‘cave’ where the orebody previously resided. Specific examples of cave mining techniques include block caving, panel caving, inclined-drawpoint caving, cut and fill mining, shrinkage stopping, sublevel longhole mining, room-and-pillar mining and front caving.
Cave mining is typically used to mine copper, copper-gold, iron and molybdenum. It can also be used in the extraction of kimberlite and lamproite in the mining of diamonds.
Block Cave Mining Techniques
The most commonly used cave mining technique is block caving. Block caving is a large-scale mining method that is particularly useful for mining low-grade or disseminated ore bodies which are at too great a depth to be exploited through open-cast mining. This mining technique gets its name from the layout of the mine which divides the ore into large sections or ‘blocks’.
To begin, an underground tunnel is undercut which involves digging the tunnel beneath the ore body. Next, the separate blocks are blasted from beneath so that they fracture. The orebody is then essentially rubble making it easy to extract the minerals using gravity driven processes.
The ore can flow out through a draw-point by using a funnel-shaped structure into which the blasted ore can be collected on belt conveyor systems or mine carts until they are transferred to the surface for processing. The flow of the broken orebody through the draw-points can be controlled manually.
For block caving to be a viable option, the orebody must be massive and well fractured. This technique is therefore typically used on steeply dipping orebodies.
Panel Cave Mining Techniques
A variation of block mining is panel mining, which is a process that divides the ore into sections and extracts it in a similar fashion to block mining. The difference between panel cave mining and block cave mining is attributed to the production process that moves sequentially along the length of the orebody so that only when one section of the ore is in production is the next one blasted. This organized production method has been associated with reducing development costs for mine operators.
Benefits of Cave Mining
Caving techniques are often chosen based on their high production rates that can be achieved at consistently low costs.
Cave mines are also relatively simple to operate and therefore do not require an extensive team of specialists or skilled workers, especially considering that no further drilling is required once the draw-points are set up.
Cave mining is also usually cheaper and more environmentally friendly compared to traditional open cast mining methods. Furthermore, if the drawpoints and handling facilities are correctly implemented for the specific orebody, then cave mining becomes the most cost-effective way of mining subsurface.
Recent Advancements in Block Cave Mining
In 2019, WSP USA published their work on developing a three-dimensional (3D) groundwater model that would be application for predicting groundwater levels during block cave mining projects. This project emerged in response to the tremendous amount of stress that block cave mining procedures can cause to overlying rock masses. This stress has been shown to negatively impact surrounding areas by causing an increased number of fractures, ultimately resulting in an increased hydraulic conductivity that can permanently alter surface and subsurface ground conditions.
In the WSP model, a potential new block cave will be simulated by modeling each groundwater model cell. Each groundwater model cell represents a cave, including its hydraulic properties and potential to exhibit highly dynamic rock fracturing when mined. By utilizing this type of predictive measurement tool WSP has found that mine operators can more accurately estimate which water bearing units should be altered, as well as quantify expected flows in the event that these units are encountered at some point during the mining project.
Limitations of Cave Mining
An important issue associated with cave mining is that it can make the overlying ground very unstable and can result in surface subsidence. The magnitude of subsidence is dependent on the exact mining techniques implemented, the original topography and the integrity of the overlying substrate.
The potential for these techniques to destroy an entire mine, put the mine workers in danger and severely impact the local environment and ecosystems are serious concerns that must be evaluated prior to beginning a cave mining project. Therefore, the prediction of subsidence, as well as its probable environmental and safety impacts, has become an integral part of initiating workable caving mines.
Cave Mines Across the Globe
With over 50 global cave mining projects currently active around the world, various cave mining techniques are used in a variety of situations. Some examples of successful block caving operations include:
- Northparkes (Australia)
- Palabora (South Africa)
- Questa Mine (New Mexico)
- El Teniente (Chile)
- Oyu Tolgoi (Mongolia)
A world map showing existing and planned cave mining operations from around the world. Image adapted from edumine.com
Current Popularity of Cave Mining
Cave mining is currently experiencing a resurgence in popularity as complex ore bodies deep in the ground need exploring at economically viable costs.
These techniques are currently being employed at greater depths than ever before as a result of advancements in the design, planning and modelling stages of the process. In fact, these methods can also be applied to more complex reserves and in more competent surroundings.
An increased interest in caving techniques can also be attributed to higher metal prices, a high predicted demand for metal and a reduction in near-surface orebody discoveries as a result of it becoming harder to find economically viable near-surface orebodies in recent years.
Improving Cave Mining Safety
The safety of underground mining has also improved in recent years. Not only are new mines opening, but existing mines are also taking advantage of these improvements in caving techniques by expanding their operations. As of 2015, the United States had a total of 657 active underground mining operations, whereas a total of 12,637 active surface mining operations were accounted for in the same year.
Sources and Further Reading
This article was updated on the 6th May, 2019.