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Mining is the extraction or removal of materials from the ground, using a wide variety of mining machines. Materials may be removed by scraping or digging them above ground, or drilling into underground deposits and moving the materials to processing facilities above ground. Mining machines can be used for drilling, scraping, product transport and ore processing to separate desired and waste products.
Underground mining involves drilling access holes to the ore deposits to remove them for processing. Drilling machines can bore access holes directly using very large rotating drill heads that grind up the rock and soil, and then move it away from the drill with moving belt conveyors. Blasting for rock mining may use hole-boring machines that drill smaller holes, which are then filled with explosive chemicals that remove several feet of rock at a time. Once the rock is blasted, excavating machinery can be used to remove the rock and place it on transport cars or belt conveyors.
Open-pit mining uses large holes in the ground that are excavated to the depth of the desired product, and are common for sand, gravel and copper mines. Mining machines called draglines use a moving bucket to scrape away the soil lying over the ore deposit. Draglines can move the soil to a waste pile away from the pit, or dump the material into large trucks that transport it away from the site. The same trucks, capable of carrying many tons of material at a time, can be used to move ore to processing plants nearby.
Strip mining is similar to open-pit, but typically the desired ore is closer to the surface. Draglines or large excavator front-end bucket loaders are used to remove the large quantities of undesired soil to reach the ore layers. Some mining operations will move horizontally along an ore deposit, using newly excavated topsoil to fill in the hole left after removing the ore adjacent to the current mining position. This technique allows materials to be moved only once, and can help reduce environmental impact by allowing the transferred topsoils to be stabilized and re-planted.
Sand mining is used to extract both sand for construction uses, and to mine minerals such as titanium-based ores used in paints and plastics. The metal-enriched sands can be extracted by strip mining machines, or by flooded pit mining using dredges similar to equipment used for dredging harbors and channels for ships. Chemical treatment is used to extract the desired products, and the remaining sands are often returned to the pit.
Conveyors are widely used mining machines used to transport materials within a mining area. Underground mines use belt conveyors to move ores from the drilling area to processing above ground. Large boring machines use conveyors that are attached to the drilling head, moving along as the hole progresses and taking waste rock and ore away. Another type of conveyor is an ore car, resembling a small railcar, which can be loaded with material and run along tracks to outside processing.
After ores are removed from any mining operation, grinding and processing are commonly used to separate and purify the ores. Grinding produces a more consistent product size, which can be further separated by vibrating screens. Some materials can be separated from waste soil by flotation tanks, which use tanks full of water that allow desired materials to sink or float depending on their density or weight.