5.9 - Impacts of Mining

Learning Objectives

I. Mining Basics and Terminology

• Ore: A commercially valuable deposit of a specific mineral, often a metal.

• Metal value: Metals are valuable for their properties, including heat and electricity conduction, and they are critical building materials. Iron ore, for example, is extracted to make steel.

• Economic benefits: Mining provides the low-cost energy (like coal) and raw materials (metals, minerals, sand) needed to make almost every product, from steel beams to phones, and it creates jobs.

• Resource limits: All mined resources are finite and non-renewable. Based on USGS data published in 2026, the world's known iron ore reserves would last about 54 years at 2025 mining rates, and US reserves about 110 years.
• These 'years left' numbers change over time. Higher prices and new technology can turn lower-grade deposits into reserves, so reserves often grow even while mining continues.

• Reserve: The known amount of a material (ore, coal, oil) still in the ground that can be extracted profitably with today's technology. It's measured in tons or barrels, and it's often turned into years left by dividing by how much is used per year.
• Example (iron, USGS 2026): $\frac{87{,}000 \text{ million t of iron}}{1{,}600 \text{ million t per year}} \approx 54 \text{ years}$

• Overburden: The soil, vegetation, and rock that has to be removed to get at an ore deposit near the surface. It usually gets piled up nearby.

• Tailings: The finely ground waste rock left over after the valuable mineral is separated from the ore. Tailings are often mixed with water and processing chemicals and stored as a slurry in tailings ponds behind dams, which can leak or overflow and contaminate nearby groundwater and streams.
• Real example: In January 2019, a tailings dam at an iron ore mine near Brumadinho, Brazil, collapsed. The mud buried the mine's offices and cafeteria and killed about 270 people.

• Slag: The stony waste left after smelting, when ore is heated to very high temperatures to melt out the metal. Slag can contain toxic metals that leach out if it's dumped on land.

• Lower-grade ores: Ore grade is the percentage of the valuable mineral in the ore. Miners take the richest, easiest-to-reach ores first. As those run out, they have to mine lower-grade ores, which means moving and crushing more rock and using more energy and water, producing more waste and pollution for the same amount of metal.
• Real example: Minnesota's Mesabi Range once had high-grade iron ore with more than 50% iron. As it ran out, mines switched in the 1950s and 1960s to taconite, a low-grade rock with only about 25 to 30% iron that has to be crushed, magnetically separated, and rolled into pellets before it can be used.
• Example calculation: How much ore has to be mined to get 1 metric ton of copper from ore that is 0.5% copper? $\frac{1 \text{ t copper}}{0.005} = 200 \text{ t of ore}$. If the grade drops to 0.25%, it takes $\frac{1 \text{ t copper}}{0.0025} = 400 \text{ t of ore}$. Half the grade means twice the rock, energy, and waste.

II. Types of Mining

III. Risks and Impacts of Subsurface Mining

• High cost and danger: It's much more expensive than surface mining. Companies have to dig shafts and tunnels, hold up the roof, pump out water, and ventilate the mine, and each worker can remove less coal. The danger also raises insurance and worker compensation costs.
• As the coal that's easy to reach near the surface runs out, more of it has to come from deeper subsurface mines, which pushes costs up.

• Risks to workers: Buildup of toxic or explosive gases like methane (from poor ventilation), mine collapse, fires and explosions, and breathing in coal and rock dust.

• Particulate matter: Coal mining releases a lot of soot and small particles, which cause lung damage, cancer, and respiratory issues in mine workers.
• Coal miners who breathe coal dust for years can develop black lung disease (coal workers' pneumoconiosis), which scars the lungs.

IV. Key Environmental Effects of Mining

A. Acid Mine Drainage (AMD)

1. Mechanism: Mining exposes rock that contains pyrite (iron sulfide, $\text{FeS}_2$, a common mineral, not an element). When water and oxygen reach the pyrite, they react with it to form sulfuric acid. This happens in tunnels, open pits, and waste piles, and it can keep going for decades after a mine is abandoned.

2. Water contamination: The sulfuric acid washes into nearby rivers, streams, and potentially groundwater.

3. Toxic metal solubilization: The acid lowers the pH of the water, which makes toxic metals like mercury, lead, and aluminum more soluble, meaning they dissolve more easily.

4. Ecological impact: The low pH combined with high metal content kills aquatic life and other organisms that cannot tolerate those conditions.

B. Atmospheric Impacts

• Methane release: When mining coal, methane has to be vented out of the mine to prevent explosions. Methane is a potent greenhouse gas that contributes to climate change.

• Particulate matter: Explosions from mountaintop removal and the processing of coal release dust, soot, and small particles into the air, which damage people’s lungs.

C. Land and Water Impacts

• Habitat loss: Surface mining destroys the plants, vegetation, and soil, taking habitat away from many organisms.

• Erosion and turbidity: Removing root structures and disturbing the soil leads to extensive topsoil erosion. Those eroded sediments flow into rivers and streams and raise stream turbidity.

V. Mine Reclamation (Solution)