Underground mines operate by accessing ore deposits located deep beneath the surface through a network of shafts and tunnels, employing various techniques to extract the valuable materials.
Here's a breakdown of the operational process:
1. Accessing the Ore Body:
- Shaft Sinking: A vertical or inclined passageway (the shaft) is excavated from the surface to reach the ore deposit. These shafts serve as access points for personnel, equipment, and ventilation.
- Tunneling (Drifting): Once the shaft reaches the desired depth, horizontal tunnels (drifts or levels) are excavated to follow the ore body. These tunnels allow for further exploration and extraction.
- Ramps: Inclined tunnels (ramps) provide access between different levels of the mine, allowing for the movement of machinery and ore.
2. Mining Methods (Extraction Techniques):
Several underground mining methods exist, chosen based on the ore body's characteristics (size, shape, depth, stability), surrounding rock conditions, and economic considerations. Some common methods include:
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Room and Pillar: This method is used for relatively flat-lying ore bodies. Rooms (voids) are excavated, and pillars of ore are left in place to support the roof. These pillars can sometimes be partially or fully extracted later (pillar robbing) if the roof stability allows.
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Longwall Mining: A long wall of ore is extracted in a single slice, typically using a mechanized shearer. Hydraulic supports are used to hold up the roof while the shearer advances. Once the shearer has passed, the roof is allowed to collapse behind the supports. This method is highly productive but requires a large, uniform ore body.
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Cut and Fill Mining: Ore is extracted in horizontal slices, and the resulting void is backfilled with waste rock or other materials to provide support. This allows for selective mining and is suitable for steeply dipping ore bodies.
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Sublevel Stoping: This method involves drilling sublevels horizontally within the ore body at regular vertical intervals. Holes are drilled from these sublevels, and the ore is blasted. The broken ore is then drawn from the stopes (excavated areas) at the bottom.
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Block Caving: A large block of ore is undercut and allowed to collapse under its own weight. The fragmented ore is then drawn from drawpoints located below the caved block. This is a high-volume, low-cost method suitable for massive, weak ore bodies.
3. Ore Handling and Transportation:
- Loading: After the ore is broken, it is loaded onto trucks, rail cars, or conveyors using loaders or other specialized equipment.
- Hauling: The ore is transported to a central location within the mine, typically near the shaft.
- Hoisting: The ore is hoisted to the surface using a skip (a large bucket) in the shaft.
- Surface Processing: Once on the surface, the ore undergoes processing to separate the valuable minerals from the waste rock.
4. Ventilation:
- Underground mines require extensive ventilation systems to supply fresh air to workers, remove dust and gases, and control temperature. Large fans are used to circulate air throughout the mine.
5. Ground Support:
- To prevent rock falls and ensure the safety of workers, various ground support techniques are employed, including rock bolts, wire mesh, shotcrete (sprayed concrete), and timbering.
Example of Sublevel Stoping (Based on Provided Reference):
- Vertical Drilling: Drilling begins vertically downwards directly into the ore body.
- Sublevel Development: Horizontal sublevels are drilled at consistent vertical intervals.
- Blasting: A series of circular-patterned blasts are detonated from each level.
- Excavation: The demolished ore is excavated and transported to the surface.
