Model Answer
0 min readIntroduction
Underground mining, also known as subsurface mining, constitutes a crucial method for extracting mineral resources that are uneconomical or technically unfeasible to extract through surface mining techniques. It involves accessing mineral deposits located deep beneath the Earth’s surface through tunnels, shafts, and drifts. This method is particularly important for extracting resources like gold, copper, lead, zinc, and coal, often found at significant depths. The increasing demand for these resources necessitates a thorough understanding of the various underground mining methods and their associated environmental impacts, which are becoming increasingly scrutinized due to sustainability concerns.
Methods of Underground Mining
Underground mining methods are broadly categorized based on the geometry of the ore body and the ground conditions. Here's a detailed overview:
1. Room and Pillar Mining
This method is commonly used for relatively flat-lying, horizontally extensive ore bodies. It involves excavating a network of ‘rooms’ separated by ‘pillars’ of ore that provide structural support.
- Process: Rooms are excavated by drilling and blasting or continuous mining. Pillars are left intact to support the roof.
- Applications: Primarily used for coal, potash, and salt mining.
- Recovery Rate: Typically 60-80% as pillars are often left in place for safety.
2. Longwall Mining
Longwall mining is a highly efficient method used for extracting thick, continuous seams of coal or other minerals. It involves creating a long wall of ore that is progressively mined in slices.
- Process: A shearer machine travels back and forth along the longwall, cutting the coal. The roof behind the shearer is allowed to collapse in a controlled manner (caving).
- Applications: Predominantly used in coal mining, especially for thick seams.
- Recovery Rate: Can achieve recovery rates of up to 90-95%.
3. Cut and Fill Mining
This method is suitable for steeply dipping ore bodies or those with irregular shapes. It involves excavating ore in horizontal slices, then filling the void with waste rock or cemented fill.
- Process: Ore is extracted in stages, and the excavated area is backfilled to provide support for the overlying strata.
- Applications: Used for various metallic ores like copper, lead, and zinc.
- Recovery Rate: Relatively high recovery rates, often exceeding 80%.
4. Sublevel Stoping
Sublevel stoping is used for steeply dipping, massive ore bodies. It involves creating a series of horizontal sublevels within the ore body and extracting ore between them.
- Process: Ore is drilled and blasted from sublevels, and the broken ore is drawn down through drawpoints.
- Applications: Commonly used for copper, zinc, and iron ore mining.
- Recovery Rate: Typically 70-85%.
5. Block Caving
Block caving is a large-scale mining method used for massive, steeply dipping ore bodies. It involves undercutting a large block of ore, causing it to fracture and cave under its own weight.
- Process: A series of tunnels are driven beneath the ore body. Undercutting initiates the caving process, and the broken ore is drawn out from drawpoints.
- Applications: Used for large-scale copper, iron ore, and diamond mining.
- Recovery Rate: Can achieve high recovery rates, often exceeding 80%.
Impact of Underground Mining on Ground Surface and Environment
Underground mining operations can have significant impacts on the ground surface and the surrounding environment. These impacts need careful consideration and mitigation strategies.
1. Ground Surface Impacts
- Subsidence: The collapse of underground voids can cause subsidence of the ground surface, leading to damage to infrastructure, buildings, and agricultural land.
- Groundwater Contamination: Mining activities can disrupt groundwater flow patterns and potentially contaminate groundwater with heavy metals and other pollutants.
- Seismic Activity: Blasting and ground movement can induce seismic activity, particularly in areas with pre-existing geological faults.
2. Environmental Impacts
- Water Pollution: Acid mine drainage (AMD) is a major environmental concern, resulting from the oxidation of sulfide minerals exposed during mining. AMD can contaminate surface and groundwater, harming aquatic ecosystems.
- Air Pollution: Dust generated during mining operations can contribute to air pollution, impacting human health and vegetation.
- Habitat Loss: Construction of mine infrastructure (shafts, tunnels, waste rock dumps) can lead to habitat loss and fragmentation.
- Waste Rock Management: Large volumes of waste rock generated during mining require careful management to prevent environmental contamination.
3. Mitigation Strategies
- Ground Control: Implementing effective ground control measures (e.g., rock bolting, shotcrete) to prevent roof collapses and minimize subsidence.
- Water Management: Implementing water management plans to collect and treat mine water, preventing contamination of surface and groundwater.
- Waste Rock Management: Properly designing and managing waste rock dumps to minimize erosion and leaching of pollutants.
- Rehabilitation: Rehabilitating mined areas by restoring vegetation and stabilizing slopes.
Conclusion
Underground mining remains a vital method for accessing essential mineral resources. However, its inherent complexities necessitate careful planning and execution to minimize environmental and social impacts. Employing appropriate mining methods based on geological conditions, coupled with robust environmental management strategies, is crucial for sustainable resource extraction. Continued research and development of innovative mining technologies, alongside stringent regulatory oversight, are essential to ensure responsible underground mining practices in the future.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.