Mining & Resource Extraction

You’ll be able to

Distinguish surface mining methods from subsurface mining
Explain the environmental impacts of mining, including acid mine drainage
Calculate the mass of metal recoverable from ore of a given grade

Surface vs. subsurface mining

How a mineral is mined depends on how deep it lies. Surface mining removes the soil and rock (overburden) covering a shallow deposit. Its forms include open-pit mining (a huge terraced hole), strip mining (removing long strips of overburden, common for coal), and mountaintop removal (blasting off entire peaks and dumping the rubble into valleys). Subsurface (underground) mining tunnels down to deep deposits; it disturbs less surface land but is far more dangerous to miners and can cause subsidence (collapse of the ground above).

The environmental costs of mining

Mining’s impacts are severe. Removing overburden destroys habitat and causes erosion. Leftover crushed rock and processing waste, called tailings, often contain toxic metals that leach into water. The signature pollution problem is acid mine drainage: when sulfide minerals exposed by mining react with water and air, they form sulfuric acid, which drains into streams and dissolves toxic heavy metals, killing aquatic life. Mining is also energy- and water-intensive, and smelting ore releases air pollutants.

Ore grade, depletion, and reclamation

An ore is rock rich enough in a mineral to mine profitably; its grade is the percentage of valuable metal it contains. As high-grade deposits are used up, miners turn to lower-grade ore, which requires digging and processing far more rock for the same metal — raising energy use, waste, and impact. In the U.S., the Surface Mining Control and Reclamation Act (SMCRA, 1977) requires companies to reclaim mined land — restoring contours, replacing topsoil, and replanting — though reclaimed land rarely fully recovers its original ecosystem.

Metal recovered from ore

mass of metal = mass of ore × (ore grade as a decimal)

Ore grade is the percent of the ore that is the target metal. Convert the percent to a decimal (0.5% = 0.005) before multiplying.

Worked example

A copper mine processes 500 metric tons of ore that has a grade of 0.5% copper. How many metric tons of copper can be recovered (assuming complete extraction)?

1.Convert the ore grade to a decimal: 0.5% = 0.5 / 100 = 0.005.
2.Multiply the ore mass by the grade: 500 t × 0.005.
3.Compute: 500 × 0.005 = 2.5.
4.So 500 tons of this ore yield 2.5 tons of copper — meaning 497.5 tons become waste rock and tailings.

Answer: 2.5 metric tons of copper. The huge ratio of waste (497.5 t) to product (2.5 t) shows why low-grade mining generates so much tailings and environmental impact.

Checkpoint

Sulfide minerals exposed by a coal mine react with air and water to form sulfuric acid, which drains into a nearby stream and kills the fish. This process is called:

Watch out

Don’t confuse overburden with tailings. Overburden is the soil and rock removed to reach the ore; tailings are the crushed waste rock left after the valuable mineral is extracted. Tailings are the bigger pollution hazard because processing concentrates toxic metals in them.

Checkpoint

As the highest-grade ore deposits are depleted and miners switch to lower-grade ore, what happens to the environmental impact of obtaining the same amount of metal?

On the exam

For ore-grade calculations, convert the percentage to a decimal before multiplying (0.5% → 0.005). Then notice the waste-to-product ratio — AP loves to ask you to interpret how much waste rock is generated, which ties the math directly to the environmental impact.

Answer the 2 checkpoints as you read.