There are two ways to extract a mineral – by digging it up, or accessing it by tunnels. This pretty much sums up the comparison of surface vs. underground mining. But is it that simple? For a better understanding, ScienceStruck gives more differences between these two methods.
Did You Know?
In the past, coal miners carried a caged canary (bird) while working in underground tunnels. If the canary died, it was a sign that toxic gases were present inside, and the mine need to be evacuated.
Throughout the 1850s, hundreds of thousands of migrants made a beeline to California in the anticipation of finding gold and making a fortune. This event, aptly named the California Gold Rush, started out pretty simple. All that the miners had to do was pick up any gold flakes or nuggets they found on the ground. Later, as the metal became harder to find, miners began scooping up gravel found in rivers and streams in metal pans to filter out any gold. Finally, in the decades that followed, gold became even rarer, and as such prospective miners turned their attention to extracting it directly from rocks in which it occurred.
The difference between these techniques is easy to understand. The first gold seekers were lucky enough to stumble upon ores, or impure forms of gold, that were directly accessible from the Earth’s surface. As mining progressed, the ore deposits began running out, making it necessary to seek them deeper inside the ground. This historical event highlights the difference between two techniques of mining which are used even today – surface and subsurface mining. Let us compare and contrast them further.
Surface Vs. Underground Mining
- In surface mining, the ore is accessed directly from the Earth’s surface, and contact is maintained with the surface throughout the operation.
- Underground or subsurface mining is accomplished with the help of tunnels going into the Earth, and does not occur on the surface.
- In surface mining, the topsoil and bedrock is removed to access the ore; all done from the surface.
- In underground mining, the bedrock is kept intact, and tunnels are used to access the ore from below.
Type of Ore
- Surface mining is suitable for large, low-grade ore deposits which occur below a thin layer of rock, or alluvial deposits found in sand and riverbeds.
- Underground mining is used for small, high-grade deposits covered with a thick overburden (soil and rock above the ore), or for deep and sloping deposits.
- In all methods of surface mining, first, the overburden is stripped off using earthmovers. Then, bucket-wheel excavators remove the ore, which is loaded into haul trucks with shovel loaders. When the deposit is exhausted, the overburden is refilled in the crater, and the land is restored with the local vegetation.
- In most underground mining methods, deep vertical tunnels called shafts are drilled into the ground, along with a set of horizontal tunnels called drifts from the shaft bottom to access the ore. Then, longwall and continuous miners break up the ore deposit, which is transported back to the surface by conveyors.
Types of Methods
- Open-pit Mining: Removing ore to leave a crater.
- Quarrying: An open-pit mine for construction materials.
- Strip Mining: Ore is removed in parallel strips.
- Mountaintop Removal: Top of a mountain is blasted to remove deep ore.
- Dredging: Ore is removed from a river bottom.
The main methods of underground mining are:
- Room and Pillar Mining: Removing ore, while leaving behind some for roof support.
- Longwall Mining: An edge of the ore is sliced off in a to-and-fro pattern.
- Cut and Fill Mining: Ore removed from the tunnel, which is then filled with waste.
Advantages and Disadvantages
- Most common mining method
- 95 – 100% ore is recovered
- Freedom to use heavy equipment
- Low cost
- Less labor required
- Ore can be processed on site
- Large-scale land disruption
- Massive ecological damage
- Explosives cause noise pollution
The benefits and drawbacks of underground mining are:
- Few environmental impacts
- Minimal surface disruption
- Mining unaffected by adverse weather
- Low productivity
- Higher cost and energy requirements
- Dangers of radiation and toxic gases
- Accidents like tunnel cave-ins
- Higher injury potential
- Underground tunnels cause surface subsidence
- Requires more labor and sophisticated equipment
- Surface mining is commonly used to extract coal and copper, and increasingly, precious metals like gold.
- Underground mining is used for gold, platinum, zinc, lead, and increasingly, coal.
As can be seen, surface mining is much more advantageous than its counterpart. However, when an outcropping ore body stretches deep inside the Earth, surface methods can be used to begin the mining operation, which then need to be continued further by underground mining.