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This chapter explores minerals and mineral resources, including their types, formation processes, and extraction methods. It covers metallic and nonmetallic minerals, ore minerals, subsurface and surface mining techniques, and the process of smelting.
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16.1 Minerals and Mineral Resource A. What is a Mineral? • Mineral is a naturally occurring, inorganic solid that has a characteristic chemical composition and physical properties. • The atoms of minerals are arranged in regular repeating geometric patterns. • Native elementsare minerals made of only elements (gold, silver and copper) • Most minerals are compounds
B. Ore Minerals • Ore minerals are minerals that are valuable and economical to extract. • Gangue minerals are minerals that have no commercial value • 1. Metallic Minerals • Metals conduct electricity, have shiny services and are opaque • Valuable metallic minerals are native elements such as gold, silver and copper. • 2. Nonmetallic Minerals • Nonmetals tend to be good insulators, have shiny or dull surfaces and may allow light to pass through them. • Nonmetallic minerals can be native elements or compounds.
C. How do Ore Minerals Form? The types of minerals that form depend on the environment in which they form 1. Hydrothermal Solutions • Hydrothermal solutions are hot subsurface waters that contain dissolved minerals. • As they flow through cracks in rocks they dissolve minerals • New minerals crystallized out of the solutions then fill fractures to form ore deposits called veins 2. Evaporites • Water in the seas or lakes evaporates deposits of salts are left behind • Evaporates form in arid regions where rates of evaporation are high • Include rock salt and gypsum.
D. Mineral Resources and their Uses • Some metals can be pounded or pressed into various shapes or stretched very thinly • Some are good conductors of heat and electricity • Alloys are formed when two or more metals are combined • Nonmetals are most widely used minerals in the world • Gemstones are nonmetallic minerals prized purely for their beauty, rarity, or durability.
19.2 Mineral exploration and Mining A. Mineral Exploration • 1st step in finding an ore deposit is exploring rock for mineralization. • Planes carry instruments that identify patterns in the land • 2nd step rock samples are taken from the areas and analyzed to determine ore grade
B. Subsurface Mining • Subsurface mining is how ore deposits beneath Earth’s surface. • Room-and-pillar mining is a common method used to extract coal and salt. • Networks of entries (rooms) are cut into a horizontal layer of coal. • Between each room is a pillar of coal left to support t the roof. • When mining is complete the pillars of coal are removed.
1. Longwall Mining • Longwall mining is a more efficient way to remove coal form a subsurface seam. • A machine (shearer) moves back and forth across the face of a coal seam. • The coal is sheared from the surface and falls on a conveyor then transported out of the mine. 2. Solution Mining • Soluble mineral ores can be removed by solution mining. • Hot water is injected into the oar and dissolves it. • Compressed air is pumped into the dissolved ore and lifts it to the surface.
C. Surface Mining • Surface mining methods used when ore deposits are located close to Earth’s surface. • Open-pit mining is often used to mine large quantities of near-surface • Ore is mined downward, layer by layer.
1. Surface Coal Mining • Overburden is rock that covers near-surface coal seams • 1st step is to remove and set aside the soil • 2nd overburden is removed by heavy equipments. • 3rd loaders enter the pit and remove the exposed coal • 4th once coal is removed the pit is filled with overburden, contoured and covered with the soil
2. Quarrying • Building stones (granite and marble) are mined in quarries. • Aggregates(sand, gravel, and crushed rock) are the main products of quarrying.
3. Solar Evaporation • Solar evaporation is the process of placing sea water into enormous shallow ponds. • Sun evaporates the water and increases the concentration of sodium chloride • This method of salt production is used in areas that receive little rainfall and have high evaporation rates. • Solar evaporation is used largely in developing countries and 30% of worlds salt comes from solar evaporation.
D. Placer Mining • Placer deposits are minerals that are concentrated by wind and water into surface deposits. • Streams transport mineral grains to a point where they fall to the streambed and are concentrated. • Stream placers often occur at bends in rivers where the current slows. • Gold, diamonds and other heavy minerals are mined by dredging.
E. Smelting • Smelting is where crushed ore is melted at high temperatures in furnaces to separate impurities from molten metal. • Flux bonds with impurities and separates them from the molten metal • Molten metal falls to the bottom of the furnace and is recovered. • The Slag (impurities)form a layer on the top • Gases (sulfur dioxide) are captured so they do not enter the environment
F. Undersea Mining • Ocean floor contains significant mineral resources • Cost and great waters depths at which minerals are found are two reasons undersea mining has not been successful.
16.3 Mining Regulations and Mine Reclamation • Because of environmental impacts of mining, it is the most heavily regulated industries in the US. • Reclaiming the land or returning it to its original condition after mining is a part of every surface coal mining operation. A. The Environmental Impacts of Mining • Billions of dollars are spent to clean up abandoned mines.
1. Air and Noise Pollution • At surface coal mines dust is produced by removing, loading, hauling and dumping soil and overburden. • Dust is also produced when ore is blasted apart • Noise is created by equipment and blasting • Most surface mines are not located near urban populations • Regulations in US forbid mining operations to allow dust or noise t exit the area being mined
2. Water Contamination • Water resources can be negatively impacted by mining • Containments can wash into streams where they can harm or kill aquatic life • Minerals that contain a lot of sulfur and react with water to produce dilute sulfuric acid.
3. Displacement of wildlife • Removing soil from a surface mine site strips away all plant life. • With the removal of plants animals will leave the area • When the soil is returned to the site different plants and animals may establish themselves. • Dredging disturbs river bottoms and destroys aquatic plant live. • Disturbance of a riverbed can cause sediments to contaminate a river for up to 10 km
4. Erosion and Sedimentation • Excess rock from mines is dumped into large piles called dumps. • Running water erodes unprotected dumps and may harm water quality and aquatic life 5. Soil Degradation • Soil at a mine is removed from the uppermost layer downward • If soils is not removed and stored in separate layers the soil may be nutrient poor when it is reclaimed. • Soil rich in sulfur once exposed t water and oxygen release acid. • If acidified soil is returned to the mine site it may be difficult for plants to grow.
6. Subsidence • Subsidence is the sinking of regions of ground with little or no horizontal movement. • Can occur when pillars in a mind collapse or the mine roof or floor fails • Buildings, houses, roads, bridges, underground pipelines and utilities may be damaged 7. Underground Mine Fires • Fires in underground coal seams are one of the most serious environmental consequences of coal mining • Lighting, forest fires and burning trash can cause coal-seams fires. • These fires are hard to put out and often left to burn out (which may take decades). • They release smoke and gasses that can cause respiratory problems.
B. Mining Regulation and Reclamation • Mines in US are regulated by federal and state laws • Mining company must comply with Clean Water Act and the Safe Drinking Water Act. • All mining operations must comply with the Endangered Species Act.
1. Reclamation • Reclamation is the process of returning land to its original or better conditions after mining is completed. • The Surface Mining control and Reclamation Act of 1977 (SMCRA) create a program for the regulation of surface coal mining. • The act set standards that minimize the effects of coal mining on environment
2. State Regulation of Mining • Mining companies must obtain permits before mining • A bond forfeiture program is where a company must post a funds (a bond) before mining project begins • The states use the funds to reclaim the sit if the company does not reclaim the site according to the standards. • State agencies are responsible for inspecting mines to ensure compliance with environmental regulations. • Pennsylvania has large projects to reclaim abandoned mine lands.
