Strip mining is classified as a form of surface mining, operating entirely above ground. The fundamental difference between surface and subsurface mining lies in the proximity of the mineral deposit to the Earth’s surface. Strip mining is employed to access mineral seams that are relatively shallow, which makes the extensive removal of overlying material a practical strategy. The technique is based on removing all material from the surface down to the desired deposit, contrasting sharply with underground methods that leave the surface largely undisturbed.
Classification: Strip Mining is Surface Mining
Strip mining is a non-tunnel approach that falls under the broad classification of surface mining techniques, alongside methods like open-pit mining and mountaintop removal. This classification applies because the entire operation is conducted in the open air directly on the Earth’s surface, without the need for vertical shafts or horizontal tunnels. The method is designed for extracting near-surface, relatively flat-lying deposits spread over a wide area.
The defining characteristic is the systematic removal of the overburden, which is the soil, vegetation, and rock layer covering the mineral deposit. This process exposes the mineral seam directly, allowing for extraction using heavy machinery. Strip mining is only economically viable when the overburden layer is not excessively thick relative to the thickness and value of the underlying deposit. The practice is often divided into area mining for flat terrain and contour mining for hilly or mountainous regions.
The Core Steps of the Strip Mining Process
The operational sequence begins with comprehensive site preparation, involving surveying the area and clearing all vegetation and topsoil. This initial layer of topsoil is segregated and stored separately for use in later reclamation efforts. Following clearing, the primary step is overburden removal, which involves excavating the rock and subsoil covering the mineral seam.
If the overburden consists of hard rock, it may require drilling and controlled blasting to fracture the material before it can be efficiently moved. Massive machinery, such as draglines and power shovels, then transport the broken overburden, often placing it into the trench created by the previous strip of excavation. This continuous process creates a long, open trench that fully exposes the target mineral seam.
Once the deposit is exposed, the extraction phase begins, where the mineral, such as a coal seam, is removed using specialized loaders and trucks. The process is often sequential, meaning the overburden from a new strip is immediately used to backfill the trench left by the strip that was just mined out. The final stage, known as reclamation, involves replacing the stored topsoil, contouring the land to match the approximate original shape, and reestablishing vegetation to stabilize the soil.
How Surface Mining Differs from Subsurface Mining
The distinction between surface and subsurface mining is based on the method of access and the depth of the resource. Surface mining, including strip mining, is conducted entirely from the open ground, resulting in a large land footprint and significant surface disturbance. This method is highly effective for mineral deposits that occur in broad, horizontal layers relatively close to the Earth’s surface.
In contrast, subsurface mining, also known as underground mining, is used to reach deeper deposits through the construction of vertical shafts and horizontal tunnels. Subsurface operations disturb a minimal amount of surface land but involve more complex engineering and greater safety risks for workers due to the confined underground environment. The two types are also treated differently under federal law. The Surface Mining Control and Reclamation Act of 1977 (SMCRA) specifically regulates the environmental effects of surface coal mining in the United States. SMCRA mandates that surface mines meet specific performance standards and requires companies to post a bond to ensure the land is reclaimed to its pre-mining condition after operations cease.
Common Resources Mined Through Stripping
Strip mining is the preferred method for extracting materials that form in extensive, shallow beds that are uneconomical to access through deep tunneling. The most common material extracted using this technique is coal, particularly lignite and bituminous coal, which often occur in wide, horizontal seams near the surface. Strip mining accounts for a significant portion of the world’s coal production.
Beyond coal, this method is also extensively used for extracting industrial minerals and certain metallic ores. Examples include phosphate rock, a source material for agricultural fertilizers, and gypsum. Strip mining is also employed to access deposits of bauxite, the primary ore from which aluminum is refined.