Minerals and Mining Chapter 14
What is a mineral? • Naturally occurring, inorganic solid with a definitive chemical composition and crystalline in structure.
High-Grade Ores • Rocks that contain large enough quantities of minerals to be profitably mined
Economic Mineralogy • Study of minerals that are valuable for manufacturing and essential to domestic and international commerce. • Metal-bearing • Non-metal bearing
Metal Ores • We are very dependent on the unique lightness, strength, and malleability of metals. • Iron (740 million metric tons annually) • Aluminum (40 million) • Manganese (22.4 million) • Copper and Chromium (8 million) • Nickel (.7 million) • Consumed in the US, Japan, and Europe (in that order) • Found in many countries, usually in mountainous areas where the heat and pressure tend to concentrate the ores.
Nonmetal Ores • Gemstones and Precious Metals • Their monetary value bankrolls, criminals, gangs, terrorism, inhumane labor conditions. • Sand and Gravel - greatest volume and dollar value • Brick and concrete construction, paving, sandblasting and glass production • Limestone • Concrete and building stone, plaster, cement • Evaporites • Gypsum for wallboard, salt for roads • Sulfur • Sulfuric acid for car batteries
Mining • Mining is the extraction of valuable minerals or other geological materials from the earth. • The process of mining from discovery of an ore body to extraction of minerals consists of several distinct steps. • Discovery • Feasability • Development • Mine Operation • Reclamation
Mining Techniques • Can be divided into 2 main types • Surface • Sub-surface(underground) • Surface mining is much more common • 85% of minerals in the United States, including 98% of metallic ores
Mining Techniques • Surface Mining • Extracts 90% of nonfuel mineral and rock • Extracts 70% of coal • Subsurface Mining • Extracts coal and metal ores too deep to reach by surface mining
Surface Mining • Strip out overburden (becomes spoils) • Four land methods possible • Open-pit (quarry) • Area strip mining (flat terrain) • Contour strip mining (hilly terrain) • Mountaintop removal • Clean up (reclamation)
Surface Mining • “Buckets”scrape surface ore
Mining Trucks *To the left is a photograph of a Liebherr 360 ton (327 metric ton) haul truck. This unit is powered by a 2750 horse power engine and weighs 443,000 pounds (177 tons) empty...
Rehabilitation • Waste dumps are contoured to flatten them out, to further stabilize them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, known as acid mine drainage. • This is then generally covered with soil, and vegetation is planted to help consolidate the material
Cont… • Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals • It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment
Strip Mining • Rainwater leaches chemicals (H2SO4) into ground water (acid drainage)
Mountaintop Removal • A form of coal mining that uses explosives to blast overburden off the top of mountains. Excess mining waste or overburden is dumped by large trucks into nearby valleys. • Coal companies are often granted waivers and instead reclaim the mountain with topsoil substitute instead of putting back the original topsoil.
Mountaintop Removal and Valley Fill (WV) The top of a mountain has been pushed into a valley
Environmental Impact • sites expel dust and fly-rock into the air, which can disturb or settle onto private property nearby. This dust may contains sulfur compounds, which corrodes structures and is a health hazard • main issue has been over the physical alteration of the landscape • extensive tracts of deciduous forests destroyed by mountaintop mining support several endangered species and some of the highest biodiversity in North America
Landfill Mining • process whereby solid wastes which have previously been land filled are excavated and processed. The function of landfill mining is to reduce the amount of landfill mass within the closed landfill and temporarily remove hazardous material to allow protective measures to be taken before the landfill mass is replaced. In the process, mining recovers valuable recyclable materials, a combustible fraction, soil, and landfill space
Subsurface Mining • Subsurface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits • Techniques include: • Drift mining • Slope mining • Shaft mining • Long wall mining • Room and pillar mining
Slope Mining • A sloping access shaft travels downwards towards the coal seam.
refers to the method of excavating a vertical or near-vertical tunnel from the top down, where there is initially no access to the bottom Shaft Mining
Environmental Effects of Mining • Disturbance or removal of land surface • 80,000 metric tons of particulate matter and 11,000 metric tons of sulfur dioxide from nonmetal mining alone • EPA lists more than 100 toxic air pollutants • Chemical and sediment runoff • When sulfur bearing minerals are exposed to air and water, they produce sulfuric acid (Acid Miner Drainage). • Vast quantities of ore must be crushed and washed to obtain small quantities of metal; enormous amounts of freshwater are thereby contaminated with acid, arsenic, heavy metals.
Environmental Effects of Mining • Mining • Placer Mining - hydraulically washing out metals deposited in streambed gravel by using water cannons to blast away stream beds • Destroys streambeds and fills water with suspended solids.
Placer Mining • Huge amounts of water are used to separate gold ore (by density) that has been weathered and deposited in streams • Mercuryoften used to bind gold