The Three Major Types of Sub-Surface Mining

Sub-surface mining, also known as underground mining, is a technique used to extract minerals and resources from beneath the Earth's surface. This method is often employed when the desired materials are located deep below the surface or are situated in deposits that are not easily accessible through surface mining methods. There are three major types of sub-surface mining, each with its own specific methods, equipment, and applications. These types are room and pillar mining, cut and fill mining, and sublevel stoping. This article will delve into each method, explaining their processes, advantages, disadvantages, and typical applications.

1. Room and Pillar Mining

Room and pillar mining is one of the oldest and most widely used methods of underground mining. This technique is primarily employed in the extraction of coal, gypsum, and potash. The basic principle involves creating a series of rooms or chambers in the ore body while leaving pillars of ore to support the roof of the mine.

Process:

• Development Phase: Initial work involves driving tunnels or "drifts" into the ore body to establish the layout of rooms and pillars.
• Extraction Phase: Once the layout is in place, miners extract ore from the rooms while leaving the pillars intact to support the mine roof.
• Support Structures: The pillars are often designed to be large enough to withstand the stress of the overburden, but their size and placement can be adjusted based on the rock conditions and ore body geometry.

Advantages:

• Flexibility: The method is adaptable to varying ore body shapes and sizes.
• Safety: By leaving pillars of ore to support the mine roof, the risk of collapse is minimized.
• Efficiency: The method allows for the extraction of a significant portion of the ore body.

Disadvantages:

• Ore Recovery: Not all of the ore can be extracted due to the presence of pillars, which can result in lower recovery rates.
• Subsidence: The removal of ore can lead to ground subsidence on the surface, affecting land use and infrastructure.

Applications: Room and pillar mining is commonly used in coal mines, especially in the United States and Canada. It is also employed in the mining of gypsum and potash.

2. Cut and Fill Mining

Cut and fill mining is a method designed for mining steeply dipping ore bodies and is particularly effective in irregular or complex ore bodies. This technique involves mining out ore in horizontal slices or "cuts," followed by backfilling the void with material to support the overlying rock.

Process:

• Cutting Phase: Miners extract ore in horizontal slices, often starting from the bottom of the ore body and working upwards.
• Filling Phase: After a slice is extracted, the void is backfilled with waste rock, tailings, or a specially prepared fill material.
• Repetition: The process is repeated slice by slice until the entire ore body has been mined.

Advantages:

• Ground Stability: The backfilling process supports the surrounding rock, reducing the risk of ground subsidence.
• Versatility: The method can be adapted to various ore body geometries and is effective in steeply dipping deposits.
• Resource Utilization: Cut and fill mining allows for high ore recovery rates, with minimal waste rock.

Disadvantages:

• Cost: The need for backfilling materials and additional infrastructure can increase the cost of mining.
• Complexity: The method requires careful planning and execution to ensure stability and efficiency.

Applications: Cut and fill mining is used in the extraction of metals like gold, silver, and copper, particularly in deposits with irregular shapes or steep inclines. It is also used in some coal mining operations.

3. Sublevel Stoping

Sublevel stoping is a mining method used for extracting ore from large, steeply dipping ore bodies. This technique involves creating a series of horizontal sublevels within the ore body, which are then mined out in a step-by-step process.

Process:

• Drilling and Blasting: Miners drill blast holes along the ore body and detonate explosives to break up the ore.
• Ore Extraction: The broken ore is collected and transported to the surface.
• Stope Formation: As ore is extracted, the stope (the mined-out cavity) expands vertically, and new sublevels are developed above the previous ones.

Advantages:

• High Recovery Rates: Sublevel stoping can achieve high ore recovery rates due to its ability to mine large volumes of ore.
• Flexibility: The method can be adapted to varying ore body shapes and sizes.
• Productivity: The use of mechanized equipment and drilling techniques can enhance productivity.

Disadvantages:

• Ground Stability: The method requires careful management of ground stability to prevent collapse or rock falls.
• Ventilation: Adequate ventilation is necessary to ensure safe working conditions due to the presence of dust and fumes.

Applications: Sublevel stoping is commonly used in the mining of metal ores such as copper, gold, and zinc. It is well-suited for deposits with steep dips and significant vertical extent.

Conclusion

Each of the three major types of sub-surface mining—room and pillar mining, cut and fill mining, and sublevel stoping—has its own set of advantages and disadvantages, making them suitable for different types of ore bodies and mining conditions. Understanding the specific requirements and characteristics of each method is crucial for optimizing resource extraction and ensuring the safety and efficiency of mining operations.

By selecting the appropriate sub-surface mining method based on the ore body's geometry, stability, and desired recovery rates, mining companies can effectively manage resources and minimize environmental impacts. As technology advances and mining techniques evolve, these methods continue to play a critical role in the extraction of valuable minerals from beneath the Earth's surface.