Strip Mining

The spoil banks are leveled and the topsoil replaced; fertilization and replanting, usually with grasses or trees for erosion control, and subsequent monitoring of revegetation efforts, complete the process. In large operations, the leveling and replanting coincide with mining, which is ideal since this rapidly rebuilds the vegetation cover. In hilly terrain, only a few cuts are all that is usually profitable because the depth of overburden increases rapidly into the hillside. Since the worst complications as a result of strip mining occur on hillsides, the environmental price for a limited amount of coal is very high.

Types of Strip Mining Techniques

The mining process starts at the edge of the deposit and moves inward in successive strips until the entire deposit is mined. As the dragline or continuous excavator moves the overburden to the adjacent empty pit where the coal has been removed, the rock swells in volume. Earth or rock increases in volume, called the swell factor, when the material is removed from its in situ or in-ground state and placed into a pit or on the surface.

Frequently Asked Questions about Strip Mining

Coal extraction follows behind power shovels, leaving a flat, canyon-like cut. Upon completion of a row, the shovel starts back in the opposite direction, placing the new overburden in the now-empty cut. In large mines rotary drills are used to drill holes with diameters ranging from 150 to 450 mm (about scammed by xcritical 6 to 18 inches).

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1. All of these would be included in an inverted triangle with its sides corresponding to the slope angle, its base lying on the surface, and its apex located in the ore block under consideration.
2. Spoil handling design goals for strip mining surface methods that utilize draglines and continuous excavators also include the minimization of spoil haulage distance.
3. Mine plan alternatives are evaluated to minimize the distance that spoil volumes are moved from the beginning centroid of mass to the ending centroid of mass.
4. 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.

Underground Mining Guide

The common strip-mining techniques are classified as area mining or contour mining on the basis of the deposit geometry and type. The cycle of operations for both techniques consists of vegetation clearing, soil removal, drilling and blasting of overburden (if needed), stripping, removal of the coal or other mineral commodity, and reclamation. Numerous cores are drilled to determine the depth, thickness, and quality of the coal, and to assess the difficulty of removing the overburden , which consists of topsoil and rock above the resource. If caprock is encountered, expensive and time-consuming blasting is required, a frequent occurrence in the United States. Economic analysis then determines the area and depth of profitable overburden removal.

The soft and unconsolidated overburden can be stripped and removed by dragline or shovel to expose a coal seam and metallic ore. The overburden might need drilling at grid spacings of 7.5 m × 7.5 m–15 m × 15 m depending on its hardness and thickness. Production drilling and blasting continue in advance with the movement of dragline/shovel. Open-pit mining is a type of strip mining that involves the excavation of a large, open pit in the ground.

Strip Mining Types, Environmental Impacts and Solutions

Although open-pit mines and underground mines are the two most common mining strategies, placer mining and solution mining also have been used for mineral extraction. Placer mining involves xcritical cheating excavation of river or stream sediments and the separation of valuable minerals by gravity, selective flotation, or by chemical extraction. Most solution mining is by heap leaching, in which the extractant solution is trickled over broken ore on the surface or in underground workings; less common is injection into underground aquifers. The consequence of the excavation of open pits and other mining-related disturbances is that sulfide minerals previously isolated from the atmosphere are exposed to oxygen.

The range diagram allows the mine planner to identify the equipment dump height required to keep the displaced overburden (spoil) from crowding the machinery and mining operations. In certain cases of mining multiple coal seams from one pit, a coal seam can provide the boundary between the prestrip and strip elevations. Contour strip mining is a type of area strip mining that is used on hilly or mountainous terrain. This method involves removing the overlying rock and soil layers in a series of parallel strips that follow the contours of the landscape. The waste rock and soil are then placed in the lower strips to create a stable base for the next strip.