Methods of Extraction
Surface and underground methods, chosen based on ore depth, grade and cost.
The method of extraction depends on:
- Depth of the ore or rock deposit.
- Grade of the ore (concentration of useful mineral).
- Economic feasibility (profit vs. cost).
Quarrying:
- Removes rock or mineral from near the surface by cutting, blasting and excavating.
- Used for: limestone, granite, sand, gravel, marble.
- Rock is blasted with explosives, then crushed and processed.
- Creates a large pit or open face in the landscape.
Open-pit (open-cast) mining:
- A large, stepped pit excavated into the surface.
- Used when ore is close to the surface but spread over a wide area.
- Examples: copper mining (Bingham Canyon, USA), iron ore (Pilbara, Australia), coal.
- Cheaper per tonne than deep mining; very large machinery used.
- Produces enormous waste rock (overburden) that must be dumped nearby.
Deep (underground/shaft) mining:
- Vertical shafts and horizontal tunnels driven into the Earth to reach ore at depth.
- Used when ore is deep underground and too expensive to uncover by surface methods.
- Examples: gold (South Africa β up to 4 km deep), coal, diamonds.
- More expensive than surface mining; dangerous (roof collapse, flooding, toxic gases).
- Less surface disturbance than open-pit, but underground impacts (subsidence).
Processing after extraction: Once ore is extracted, it must be processed:
- Crushing and grinding β reduce ore to small particles.
- Concentration β separate the mineral from waste rock (gangue).
- Smelting / refining β heat or chemical treatment to extract pure metal. These stages consume large amounts of energy and water.
- Quarrying: surface rock/mineral, blasting and excavating.
- Open-pit: large stepped surface pit, efficient, large waste volumes.
- Deep mining: shafts/tunnels for deep ore, expensive and dangerous.
- Processing: crush β concentrate β smelt β energy and water intensive.