Key terms: 1.Overburden: the soil & rock that lies above the economically important rock. 2.Gangue: worthless minerals/material that surrounds ore 3.Smelting: using heat & chemicals to turn ore into useable mineral 4.Tailings: piles of waste left behind after extraction, contains gangue
Advantages Income! Revenues for cities, states and countries Employment Progress – buildings, cars, electronics Uses lots of energy Disturbs land Erodes soil Produces a lot of waste Pollutes air, water, soil Disadvantages
Surface mining Removal of shallow deposits Overburden removed Rock/soil on top of deposit Discarded as spoils Used in 90% of non-fuel mineral/rock resources Used in 60% of coal mined in U.S. Removal of deep deposits Often used for coal and metal ores Deep vertical shaft is dug Tunnels must be blasted Machinery used to reach deposits Subsurface mining
Surface Drift Slope Shaft Hard Rock Borehole Fracking Subsurface Open Pit Strip Mountaintop Removal Placer Hydraulic Dredging
Open-pit mining Holes are dug Ores are removed Iron, copper, gold, sand, gravel, stone Used for horizontal beds of minerals Area strip mining: flat land Contour strip mining: hills Coal (70%) Strip mining
Used on hilly or mountainous terrain. Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall. Figure 15-13
Mountain top removed Exposes deposits Prominent in Appalachian mountains Ex. Coal
Gold Mining Placer Deposits (gravity separation) Panning Sluicing Dredging Hard Rock Deposits Open pit Hydraulic mining (sometimes with Hg) Subsurface - S. Africa 12, 800 feet underground Cyanide is used to extract gold
1. Scarring/disruption of land Overburden/Spoils left behind, vegetation cant grow well H2SO4 – acid runoff Sediment, erosion, loss of topsoil Subsidence, cave-ins (sink holes), explosions
2. Processing involves many chemicals (sulfuric acid, mercury, cyanide) Creates toxic waste during processing Tailings: Often stored in valleys – As, Hg, CN, H2SO4 Can collapse and get into ecosystem Streams/Groundwater polluted with waste material Tailings: H2SO4, Hg, CN (Cyanide) Overburden: Sediment Overburden: H2SO4 – leaches heavy metals such as As, Cd, Pb, Zn Air pollution from processing Highest industrial air polluter of toxic emissions!
Clean up and restore mining sites 500,000 surface sites in U.S. $70 billion to clean up Subsurface disturbs <1/10 the land that surface mining disturbs Produces less waste But…causes cave ins, explosions, fires, diseases, deaths
Designed to encourage mineral exploration on U.S. public lands and populate the West Individuals could claim land Must spend $500 to improve land Could pay $6-12 for land owned by all U.S. citizens Could build, sell, lease, use it for whatever Frozen in 1995 Some land still being transferred at 1872 prices! 1992 modification: must post bonds to cover clean up cost in case of bankruptcy Mining companies trying to weaken
surface coal mining Established a program for regulating surface coal mining and reclamation activities Established mandatory uniform standards for these activities on state and federal lands requirement that adverse impacts on fish, wildlife and related environmental values be minimized reclamation of land after mining was completed Created an Abandoned Mine Reclamation Fund for use in reclaiming and restoring land and water resources adversely affected by coal mining practices.