excavated using very powerful and large earth-moving equipment, and processing of the ore (crushing, grinding, partial refinement) is often done near the open pit. Open pits are less environmentally friendly than conventional mines because any native vegetation in the area is lost, and abandoned open pit mines eventually pool waters that are frequently contaminated. Open-pit mines are used for copper in Arizona. Strip mines: These mines are large swaths dug through ore-rich zones (common for coal). Most mines are located below the surface of the Earth, and require drilling shafts to enable workers to reach the ore below and transport it to the surface. Strip mines are used for coal in many states and other areas where the ore is buried deeply, as in Montana, where platinum and palladium ore is extracted (removed). Stope and adit mines: These mines are bored into the ground. Shafts are bored vertically, and horizontal offshoots (adits) from the shafts that lead into ore-containing portions of the subsurface are dug. Large mining vehicles that crush the rock move along veins of ore, and this byproduct is transported to the surface by rail or cable lifts. Temperatures in conventional mines are high, and the conditions are dangerousave-ins occur ofteno safety measures are very strict. The shafts and other structures are reinforced with concrete or metal supports.Panning for gold near Sutter Mill, California. Robert Holmes/Corbis. Reproduced by permission.Other ore and mineral deposits Placer deposits are concentrated metals that have been transported to streambeds (the channel through which the stream runs) or beaches. The most famous placer deposits are gold nuggets, although silver is sometimes found as well. Placer metals must be resistant to water, or they would dissolve again. The usual way to extract the placer deposits is to scoop sediment (particles of rock, clay, or silt) from the stream and sift it, leaving the larger rock behind and making the gold easier to spot. California, Alaska, Oregon, and Idaho have all had significant placer deposits of gold.Minerals and Mining 295
