Mining of Ores (College Board AP® Environmental Science): Study Guide

Impacts of mining lower grade ores

What are lower grade ores?

• Lower grade ores contain smaller concentrations of valuable minerals

  • This means they require more extensive processing to extract usable material

• As high-grade ores become depleted, mining companies must turn to lower quality deposits

Environmental impacts of mining lower grade ores

Increased resource consumption

• More energy is required to extract and process lower-grade ores

• Higher water usage is needed for chemical separation processes, increasing strain on local water sources

Greater waste production

• Mining lower-grade ores generates larger amounts of waste rock and tailings

• Tailing ponds hold toxic slurry, which can leak into surrounding ecosystems

Higher pollution levels

• More fossil fuels are burned to power mining equipment and ore processing

  • This contributes to higher CO₂ emissions

• The use of chemicals like cyanide and sulfuric acid in ore extraction increases the risk of soil and water contamination

Economic and social impacts

Rising mining costs

• Extracting minerals from lower-grade ores increases operational costs, as more ore must be processed to obtain the same yield

  • These higher costs can lead to increased consumer prices for metals and minerals

Land degradation and habitat destruction

• Larger mining operations are required to process more ore, leading to expanded deforestation, habitat destruction, and soil erosion

  • Example: In regions like the Amazon rainforest, lower-grade gold mining contributes to widespread deforestation

Surface mining

What is surface mining?

• Surface mining involves the removal of large sections of soil and rock (known as overburden) to access minerals near the Earth’s surface

• It is used for extracting coal, gold, copper, and other valuable minerals

• More common than underground mining because it is cheaper and safer, but it has significant environmental impacts

Types of surface mining

Strip mining

• Removes long strips of land to extract minerals located close to the surface

• Destroys vegetation and topsoil, leading to increased erosion and habitat loss

Open-pit mining

• Excavates large, deep pits to access ore deposits

• Used for gold, copper, and iron ore mining

• Generates massive amounts of waste rock, altering landscapes permanently

Environmental impacts of surface mining

Habitat destruction

• Deforestation and removal of vegetation disrupt ecosystems and wildlife populations

• Loss of biodiversity as species are displaced from their natural habitats

Soil erosion and degradation

• Exposed soil after mining is prone to erosion, leading to loss of fertile land

• Mining spoils (waste materials) are often acidic and prevent plant regrowth

Water pollution

• Heavy metals and chemicals from mining runoff contaminate rivers and groundwater

• Acid mine drainage (AMD) occurs when exposed rock reacts with air and water, releasing toxic sulfuric acid

Mining wastes

• Mining wastes are the unwanted materials left behind after extracting valuable minerals from ore

• These wastes include overburden, tailings, and slag, each of which poses environmental risks

Types of mining wastes

Overburden

• Soil and rock layers removed to reach ore deposits

• Often piled into spoil heaps, which can lead to habitat destruction

Tailings

• Finely ground rock and chemical byproducts left after ore processing

• Contain heavy metals, cyanide, and sulfur compounds, which can leach into water sources

• Stored in tailing ponds, which risk leakage, dam failure, and water contamination

Slag

• Residue left after smelting ores, mainly composed of metal oxides

• Can contain toxic elements like arsenic and lead, contaminating soil and groundwater

Managing and reducing mining waste

• Recycling mine waste: Some tailings and slag can be reused in construction materials or road-building

• Land reclamation: Restoring mined lands by planting vegetation and stabilizing waste piles

• Better waste storage: Improved tailing dam designs reduce the risk of spills and contamination