Strip mining is a form of surface mining that is employed to strip away a layer or seam of soil, natural vegetation, and rocks (known as overburden) to extract the mineral deposits underneath. Unlike underground mining, it is predominately used to access relatively flat sedimentary mineral reserves that are near the earth’s surface, usually coal and lignite.
There are two common techniques under the umbrella of strip mining categorized as area mining and contour mining, depending on the amounts of ore under the surface. Area mining is appropriate for near-surface, thin mineral extraction over a wide, flat terrain in a series of parallel and long strips.
Contour mining, on the contrary, progresses in a narrower and custom shaped zone where the overburden is removed, following the contours of outcrops and hilly terrain rather than long strips.
What is strip mining used to mine for?
Strip mining is commonly used to extract thin coal seams and lignite that are very close to the ground surface. Once the mineral seam buried underneath the soil and rocks are revealed through drilling and explosives, the coal resources will be mined systematically along the strips, and the overburden removal can be easily scooped off and quickly transported at the land surface.
In America, strip mining is also used for mining phosphate fertilizer in areas such as Florida, North Carolina, Idaho, and for obtaining gypsum in western United States.
Where is strip mining most common?
Strip mining occurs predominantly in the Appalachian Mountains and adjacent areas, the Central Plains from Indiana and Illinois through Oklahoma, and new mines for subbituminous coal in North Dakota, Wyoming, and Montana.
Is strip mining surface or subsurface?
Strip mining, alongside open-pit mining, and mountaintop removal mining is a non-tunnel approach and part of the broad category of surface mining. Since mining operations are conducted in the open space on the earth’s surface, where the topsoil and bedrocks can be stripped by draglines or power shovels to expose the mineral layer of ore deposits, it doesn’t require digging tunnels deep into the earth like subsurface mining (traditional underground mining).
Strip mining vs open-pit mining
Although open-pit mining is similar to strip mining, during open-pit mining operation, massive, vertical pits are created by using explosives, where the mineral materials are extracted through heavy machinery. Strip mining, however, normally creates horizontal strips or trenches from which mineral extraction or ore deposits are drilled and founded.
Statistics show that strip mining accounts for about 40% of the world’s coal mining, while open pit mines make up 80% of total coal production.
Strip mining pros and cons
Compared with other mining forms, strip mining attains a much higher recovery rate of materials, which is approximately 80%-90%, whereas underground mining only offers a roughly 50% mineral recovery rate. Meanwhile, mining companies view this method as a faster, cost-effective option with lesser safety precautions needed, because strip mines do not require tunnel access to retrieve minerals, and workers are exposed to fewer risks than those in underground mines.
However, the unwanted effects on the environment and human health generated by strip mining cannot be disputed, such as dust and noise pollution of mining activity, dissipation of endangered species resulted from land disturbance, and water pollution.
Strip mining environmental impact
Strip mining poses some undesired environmental impacts. The mining operations involve removal of vegetation, surface soil, and trees from the mined site, leaving the landscape and forests damaged and disturbing wildlife habitats, which can lead to soil erosion and reduce fertility of agricultural land. Meanwhile, vast quantities of loose topsoil can be washed away by rain and enter streams and waterways, which could cause blockage and lead to flooding.
Meanwhile, acid mine drainage is created when coal and other overlying rock unearthed are mixed with water when the site is strip mined, taking on toxic levels of minerals and heavy metals. The toxic water could contaminate groundwater, streams, soil, plants, animals, and human beings.
On the flip side, with proper management, the mined land can be restored once the strip-mining activities are over. The tailings (including ground vegetation and soil) can be put back to cover up the site and resemble the landscape before the mining operation. The empty mining site can also be filled with water to create an artificial lake.
Why is it difficult to recover land that has been strip mined?
Land rehabilitation is important after strip mining, given its direct effect on the soil and vegetation of the environment. Erosion is the most common problem that takes place at surface mines, where thousands of acres of fertile habitats for animals to survive and land to grow plants won’t be restored to their original state.
Alternative mining methods
Auger mining
This method is used to recover coal by drilling holes into a coal seam at the base of strata exposed by excavation or geologic erosion. According to Britannica, augering is normally associated with contour strip mining to recover coal for a limited depth beyond the point where stripping becomes uneconomical because the seam of coal lies far beneath the surface.
Highwall mining
This method evolves from auger mining, but it does not include the removal of overburden to expose the coal seam. Highwall mining involves remote deployment of a continuous miner to enter the coal seam at the highwall of the ultimate pit limit and attain additional coal recovery.
