Extraction of rocks and minerals from the Earth Revision Notes

Mining is the process of extracting valuable rocks and minerals from the Earth. The choice of mining technique depends primarily on the depth and location of the mineral deposit. There are two broad categories: surface mining and subsurface mining.

Surface mining is used when minerals are close to the Earth's surface, allowing removal of overlying soil and rock layers. Subsurface mining is necessary when minerals lie deep underground, requiring tunnels or shafts to access them.

• Surface mining is generally less expensive and safer but can cause more environmental disturbance.
• Subsurface mining is more complex and costly but reduces surface damage.

Surface mining involves removing large areas of soil and rock to expose mineral deposits near the surface. The main types include:

Opencast mining: Large pits are dug to extract minerals close to the surface, often used for coal or iron ore.

Open-pit mining: Similar to opencast but typically deeper and wider, used for minerals like copper and gold found in large deposits near the surface but extending downwards slightly deeper than opencast allows for. The pit walls are terraced to prevent collapse and allow machinery access safely. For example, the Bingham Canyon Mine in the USA is an open-pit copper mine several hundred metres deep and wide enough to be seen from space. Open-cut mining: This is a term sometimes used interchangeably with opencast or open-pit mining but often refers to shallower excavations where the mineral seam is horizontal and close to the surface, such as coal seams in flat terrain. Strip mining: This method removes long strips of overburden to expose mineral seams, commonly used for coal or tar sands. After extraction, the strip is backfilled and reclaimed where possible.

• Surface mining is efficient for shallow deposits.
• It allows large-scale extraction with heavy machinery.
• It causes significant landscape alteration and habitat loss.

When minerals are located deep underground, surface mining is impractical or impossible. Subsurface mining involves creating tunnels or shafts to reach these deposits.

Deep mining involves horizontal tunnels following the mineral seam underground, often supported by timber or steel to prevent collapse.

Shaft mining uses vertical shafts to access deep mineral deposits, with elevators to transport miners and ore. This method is common for gold, diamonds, and some coal mines. For example, the Kimberley diamond mine in South Africa uses shaft mining to reach deep kimberlite pipes.

• Subsurface mining reduces surface environmental impact but is more dangerous and expensive.
• It requires ventilation, lighting, and safety measures for miners.
• It is used when minerals are too deep for surface methods.

Several factors determine whether and how rocks and minerals are extracted:

Exploration: Geological surveys and sampling identify mineral deposits and estimate their size and quality.

Geology: The type of rock, mineral location, depth, and deposit shape influence mining feasibility and method choice. For example, flat-lying coal seams near the surface favour strip mining, while deep, irregular gold veins require shaft mining. Accessibility: Proximity to infrastructure such as roads, power, and water affects the cost and practicality of mining operations. Remote sites increase costs and logistical challenges. Environmental Impact Assessments (EIAs): These studies evaluate potential damage to ecosystems, water sources, and communities. Mining plans may be altered or rejected to minimise harm. Supply and Demand: Economic factors such as current market prices and demand for minerals influence whether extraction is profitable and justified. High demand and prices encourage mining even in challenging conditions.

• Mining method depends on deposit depth and geology.
• Environmental regulations can restrict or shape mining activities.
• Economic viability is essential before extraction begins.

Mining can cause habitat destruction, soil erosion, water pollution, and air quality issues. Surface mining typically has a larger footprint, while subsurface mining risks underground water contamination and subsidence.

Environmental impact assessments help identify these risks and propose mitigation measures such as land reclamation, pollution controls, and monitoring.

Economically, mining requires balancing extraction costs against mineral value. For example, if copper prices fall, a mine may close even if deposits remain. Conversely, new technology can make previously uneconomical deposits viable.

• Environmental assessments guide responsible mining.
• Economic factors determine the lifespan of mines.
• Technological advances can change extraction feasibility.