How do different mining methods reshape the geosphere and produce waste?
Compare mining methods and analyse their physical effects on the geosphere
A focused answer to the WACE Year 12 Earth and Environmental Science dot point on mining methods and geosphere impacts. Compares open-cut, underground, dredging and in-situ methods, and analyses landform change, overburden, waste rock, tailings and subsidence, with WA examples such as the Pilbara and the Super Pit.
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What this dot point is asking
SCSA wants you to compare the main mining methods and analyse how each physically alters the geosphere. This is the structural foundation for the broader impacts and rehabilitation content, so be precise about what each method does to the land and the waste it generates.
Choosing a method
The method follows the geology and economics of the deposit.
- Open-cut (open-pit) mining is used for large, shallow, lower-grade ore bodies. Overburden is removed to expose the ore, creating a widening, deepening pit. Most Pilbara iron ore and Darling Range bauxite are mined open-cut, and the Kalgoorlie Super Pit is one of the largest open pits in the country.
- Underground mining is used where ore is deep or rich enough to justify shafts and tunnels. It disturbs less surface area but leaves voids that can collapse.
- Dredging extracts loose sediment from rivers, beaches or shallow seas, used for some mineral sands and alluvial deposits.
- In-situ recovery dissolves the target mineral underground and pumps the solution to the surface, avoiding bulk excavation but risking groundwater contamination.
Physical effects on the geosphere
Whatever the method, mining changes the solid Earth in characteristic ways.
- Landform change. Open pits, waste dumps and tailings dams replace the original topography permanently.
- Overburden and waste rock. Material removed to reach ore must be stored, forming large dumps that alter drainage and can be unstable.
- Tailings. The fine waste left after the valuable mineral is separated is stored as a slurry behind dams, which must be engineered to prevent failure and leakage.
- Subsidence. Underground voids can collapse, causing the surface above to sink.
- Loss of soil and exposure to erosion. Stripping vegetation and topsoil exposes ground that erodes more easily.
Comparing footprint and waste
Open-cut mining has the largest surface footprint and produces the most overburden and waste rock, but is cheaper for bulk ore. Underground mining has a smaller surface footprint but adds subsidence risk and is costlier. Dredging churns aquatic sediment and increases turbidity, while in-situ recovery has the smallest surface disturbance but the highest groundwater risk. A strong comparison links each method to its dominant geosphere impact and the volume and type of waste it creates.
Stripping ratio and the economic limit of open-cut
A useful quantitative idea for comparison questions is the stripping ratio, the volume of overburden and waste rock that must be moved per unit of ore extracted. A low stripping ratio means little waste per tonne of ore, making open-cut cheap; as a pit deepens, the ratio rises because ever-wider walls must be cut back to keep the pit stable, so more waste is moved for each tonne of ore. Eventually the cost of moving overburden exceeds the value of the ore at depth, and this economic limit is often what triggers a switch from open-cut to underground mining on the same deposit, as happened as the Kalgoorlie Super Pit deepened. The stripping ratio therefore links the geology of a deposit directly to both the method chosen and the volume of geosphere disturbance.
Exam-style practice questions
Practice questions written in the style of SCSA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WACE 20217 marksCompare open-cut and underground mining in terms of their physical effects on the geosphere, and recommend with justification a method for extracting a deep, high-grade gold ore body beneath a town.Show worked answer →
A 7 mark answer needs a structured comparison plus a justified recommendation tied to the scenario.
- Open-cut
- Strips overburden to expose shallow ore, creating a large pit and the biggest surface footprint, with major landform change and large overburden and waste-rock dumps. It is cheaper for bulk, low-grade ore.
- Underground
- Follows deep or rich ore through shafts and tunnels, disturbing far less surface area but creating voids that can cause subsidence, at higher cost.
- Recommendation
- For a deep, high-grade gold body beneath a town, underground mining is appropriate. The depth makes open-cut impractical (vast overburden removal) and the high grade justifies the cost of tunnelling. Crucially, the small surface footprint avoids destroying the town, though subsidence must be managed by engineering and backfilling voids.
Markers reward the footprint-versus-subsidence-and-cost comparison and a recommendation explicitly justified by depth, grade and the surface constraint (the town).
WACE 20236 marksDistinguish between overburden, waste rock and tailings, and explain one geosphere management challenge associated with each.Show worked answer →
A 6 mark answer needs clear definitions plus a distinct challenge for each.
- Overburden
- The soil and rock removed to reach the ore. Challenge: it must be stockpiled in large dumps that alter surface drainage and can erode or become unstable; storing topsoil separately matters for later rehabilitation.
- Waste rock
- Uneconomic rock excavated alongside the ore. Challenge: it may contain sulfide minerals, so dumps can generate acid mine drainage and must be characterised and encapsulated.
- Tailings
- Fine processing waste stored as a slurry behind dams. Challenge: tailings dams must be engineered against failure and seepage, because collapse releases a destructive slurry and leakage contaminates water.
Markers reward correct distinctions (removed-to-reach versus excavated-uneconomic versus fine-processing-waste) and a relevant, distinct management challenge for each.