Open pit mining is a method of extracting minerals or ore from the ground by digging a pit on the surface. This technique is used when deposits are found relatively close to the surface.
The Structure of an Open Pit Mine
A key characteristic of open pit mining is the tiered, stepped design of the mine walls. This structure is essential for safety and operational efficiency.
- Open-pit mines are dug on benches or horizontal steps.
- These benches are between four and sixty-meters in size.
- The specific size of the benches depends primarily on the size of machinery used to excavate the material. Larger equipment requires wider benches.
- The walls of most open-pit mines are dug at an angle.
- The angled walls also include steps (the benches themselves serve this function visually and structurally) to prevent avalanches from occurring inside the build site.
Why the Bench and Angle Design?
The step-like structure (benches) allows machinery and vehicles to safely access different levels of the mine to extract material. The angle of the walls, combined with the benches, provides stability, reducing the risk of rock slides or collapses, which are critical safety concerns in deep excavations.
The Process of Extraction
While the structure is fundamental, the actual doing of open pit mining involves a sequence of operations performed on these benches:
- Preparation: Clearing the land and removing the topsoil (overburden).
- Drilling: Holes are drilled into the rock on the benches.
- Blasting: Explosives are placed in the drill holes and detonated to break up the rock and ore.
- Loading: Large excavators or shovels load the broken material onto haul trucks.
- Hauling: Haul trucks transport the material out of the pit to processing facilities or waste dumps.
- Scaling: Loose rocks on the pit walls are removed to ensure safety.
These steps are repeated on descending benches, creating the characteristic multi-level pit shape that defines open pit mining.
Equipment Used
The scale of open pit mining requires massive machinery, which in turn dictates the design elements like bench size.
| Equipment Type | Primary Function |
|---|---|
| Blasthole Drills | Create holes for blasting |
| Hydraulic Shovels | Load blasted material |
| Haul Trucks | Transport material |
| Dozers | Maintain roads/areas |
In summary, open pit mining is done by creating a large, stepped excavation in the earth, following a cyclical process of drilling, blasting, loading, and hauling on carefully constructed benches with angled walls designed for safety and operational access.
