Mining and Mineral Resources Chapter 16 Environmental Science
Section 16.1 • MINERALS AND MINERAL RESOURCES
Section 16.1 • What is a mineral? • A mineral is a naturally occurring, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties. • They can be made up of a single element or be a compound (atoms of two or more elements bonded together).
Ore Minerals vs. Gangue Minerals Ore Minerals Gangue Minerals Minerals that are valuable and economical to extract Mining companies have to separate the ore from the gangue. Minerals that have no commercial value For mining to be profitable, the price of the final product must be greater than the costs of extraction and refining
Metallic vs. Nonmetallic Minerals • Metallic Minerals conduct electricity, have shiny surfaces, and are opaque. • Examples are gold, silver, and copper • Nonmetallic minerals tend to be good insulators, may have shiny OR dull surfaces, and may allow light to pass through them.
How do ore minerals form? • Hydrothermal solutions are hot, subsurface waters that contain dissolved minerals. • New minerals crystallize out of these solutions and form ore deposits called veins. • Evaporites form when the water in seas and lakes evaporates and leave behind deposits of salts. • Form in arid regions where rates of evaporation are high. • Examples are halite and gypsum
Mineral Resources and Their Uses • Metals can be used for heat and electricity. • Two or more metals form an alloy. • Nonmetals can be used in construction and glassmaking. • Gemstones (diamonds, rubies, and sapphires) are prized purely for their beauty, rarity, and durability
Section 16.2 • Mineral Exploration and Mining
Mineral Exploration • The first step is to explore rock for mineralization. • Rock samples are then taken from the area. • Ore grade is then determined. • If the ore grade is high enough, the company will drill test holes. • Lastly, if the deposits are extensive enough, opening a mine may be warranted.
Subsurface mining • This method is used if ore deposit is found 50m or more beneath Earth’s surface. • Room-and-pillar mining is commonly used for mining coal. • Rooms which are a network of entries are cut into a seam. • Pillars of coal between the rooms are left standing to support roof. • Pillars are last to be removed.
Subsurface Mining Longwall Mining Solution Mining More efficient A shearer moves back and forth across the coal seam. Coal falls onto conveyor. Used in mining potash,salt, and sulfur. Very economic. Hot water is injected into the ore. Compressed air is pumped into the dissolved ore and lifts it to surface.
Surface Mining • Used when ore deposits are located close to Earth’s surface. • Open-pit mining is used to mine large quantities of coal and copper located near-surface. • Ore is mined downward, layer by layer. • Explosives break up the ore. • Ore is loaded into trucks.
Surface Mining Surface Coal Mining Quarrying First, the soil is removed. Next, overburden, rocks that cover near-surface coal seams, are removed. Once the coal is taken out, the pit is refilled with overburden and the soil is laid back on top of overburden. Used when mining granite and marble. Aggregates (sand, gravel, and crushed rock) are the products of quarrying. Could also be called an open pit.
Solar Evaporation • This involves placing sea water into enormous, shallow ponds. • The sun evaporates the sea water. • Salt crystals form. • With more evaporation, more layers of crystals form. • Salt is harvested at desired thickness. • Used in areas that receive little rainfall but have high evaporation rates (Mediterranean Sea, Australia, San Francisco) • About 30% of the world’s salt comes from solar evaporation.
Placer Mining Placer Mining Dredge Placer deposits are surface deposits where minerals are concentrated by wind and water. Most important are stream placers. Minerals fall to the streambed and become concentrated. Placer gold and diamonds are mined by dredging. A dredge is a floating barge on which buckets fixed on a conveyor are used to separate the minerals from the sediment.
Smelting • Crushed ore is melted at high temperatures in a furnace. • Flux bonds with impurities and separates them from the molten metals. • The molten metal falls to bottom of furnace. • Slag is a layer of impurities that forms on top of molten metal.
Undersea Mining • Several attempts have been made to mine the ocean since 1950s. • It is more expensive than land mining and deep ocean depths are two reasons undersea mining has not been successful.
Section 16.3 • Mining Regulation and Mine Reclamation
The Environmental Impacts of Mining • Surface mining can cause both air and noise pollution. • Dust is created in all parts of the mining process. • Noise is created by the equipment and blasting. • Due to these environmental impacts, most surface mines are not located near urban populations.
Water Contamination • Water that seeps through mines can pick up substances like arsenic. • Contaminated water from AMD or acid mine drainage happens when sulfur reacts with oxygen and water to form sulfuric acid.
Displacement of Wildlife • Removing soil due to mining strips away all plant life. • This causes animals to leave the area. • Once the soil is replaced, different plants and animals may live there. • Dredging displaces aquatic wildlife
Erosion and Sedimentation • Excess rock from mines is sometimes dumped into large piles called dumps. • Running water erodes dumps. • Sediment may harm water quality and aquatic life.
Soil Degradation • If soil is not removed and stored in separate layers, the soil may be nutrient poor when it is reclaimed. • When some minerals like sulfur are exposed to water and oxygen, the soil acidifies. • This makes it difficult for plants to grow.
Subsidence • The sinking of regions of the ground with little or no horizontal movement. • Occurs when pillars collapse or the mine roof/floor falls. • It can cause property damage and force people to evacuate their homes.
Underground Mine Fires • One of the most serious environmental consequences of coal mining. • Can be caused by lightning, forest fires, and burning trash. • Hard to put out; left to burn themselves out. • If they reach surface, can lead to respiratory problems.
Mining Regulations and Reclamation • Clean Water Act and Safe Drinking Water Act ensure contaminants from mines do not threaten water quality. • Comprehensive Response Compensation and Liability Act regulates hazardous substances released in air, soil, and water. • All mining operations must comply with Endangered Species Act to ensure mining will not affect threatened or endangered species.
Reclamation and Regulations Reclamation State Regulation of Mining Returning land to its original or better condition after mining. Surface Mining Control and Reclamation Act of 1977 minimizes the surface effects of coal mining. Mining companies must obtain permits from state agencies before mining. In some states, a mining company must post funds called a bond before mining begins. States also inspects mines.