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Bellringer. Objectives. Define the term mineral. Explain the difference between a metal and a nonmetal, and give two examples of each. Describe three processes by which ore minerals form. Mineral Resources.
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Objectives • Define the term mineral. • Explain the difference between a metal and a nonmetal, and give two examples of each. • Describe three processes by which ore minerals form.
Mineral Resources • We depend on the use of mineral resources in almost every aspect of our daily life. • However, our dependence on minerals has not come without a price. • The current challenge is to obtain the minerals that an ever-increasing world population demands at minimal cost to the environment.
What Is a Mineral? • A mineralis a naturally occurring, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties. • Minerals are made up of atoms of a single element, or of compounds. A compound consists ofatoms of two or more elements chemically bonded together. • The atoms that make up minerals are arranged in regular, repeating geometric patterns.
What Is a Mineral? • The arrangement of the atoms, along with the strength of the chemical bonds between them, determine the physical properties of minerals, • Some elements, called native elements, are considered minerals. These include the elements gold, silver, and copper. • Most minerals, however, are compounds. • The mineral quartz is made up of silica, which consists of one silicon atom and two oxygen atoms.
Ore Minerals • An ore mineralis a mineral that contains one or more elements of economic value. • During the mining process, gangue minerals, minerals with no commercial value, are extracted along with ore minerals. • Ore minerals, once separated from the gangue minerals, are refined using various methods to extract the valuable elements they contain. • For mining to be profitable, the price of the final product must be greater than the costs of extraction and refining.
Metallic Minerals • Ore minerals are either metallic or nonmetallic. • Metals have the following characteristics: • can conduct electricity • have shiny surfaces • are opaque • Many valuable metallic minerals are native elements, such as gold, silver, and copper. • Other important ore minerals are compounds of metallic minerals with nonmetallic elements.
Nonmetallic Minerals • Nonmetals have the following characteristics: • tend to be good insulators • may have shiny or dull surfaces • may allow light to pass through • Nonmetallic minerals can also be native elements or compounds.
How Do Ore Minerals Form? • Economically important ore deposits form in a variety of ways, both on and beneath Earth’s surface. • The types of mineral that form depend on the environment in which they form.
Hydrothermal Solutions • Hot, subsurface waters that contain dissolved minerals are called hydrothermal solutions. • Hydrothermal solutions dissolve minerals as they flow through cracks in rocks. • New minerals crystallize out of these solutions and then fill fractures to form ore deposits called veins. • Many economically valuable metallic ores form in this way.
Evaporites • When water in the seas or lakes evaporate, they leave behind deposits of salts called evaporites. • Evaporites form in arid regions where rates of evaporation are high. • Halite (rock salt) and gypsum are important evaporite minerals.
Mineral Resources and Their Uses • Certain metals are of major economic and industrial importance. • Some metals can be pounded or pressed into various shapes or stretched very thinly without breaking. Others conduct electricity well. • Often two or more metals are used to form alloys, which combine the most desirous properties of the metals used to make them.
Mineral Resources and Their Uses • Nonmetals are among the most widely used minerals in the world. • Gypsum, for example, is used to make building materials such as wallboard and concrete. • Some nonmetallic minerals include gemstones, prized for their beauty, rarity, or durability. • Important gemstones include diamond, ruby, sapphire, emerald, aquamarine, topaz, and tourmaline. • ARKANSAS .... FYI, has the only active diamond mine in the U.S.
Objectives • Describethe manner in which mining companies explore for new mineral deposits. • Describethree methods of subsurface mining. • Describe two methods of surface mining. • Define placer deposit, and explain how placer deposits form. • Describe the steps that take place in smelting an ore.
Mineral Exploration • Exploring rock for mineralization is the first step in finding an ore deposit. • Rock samples are taken from exploration areas and analyzed to determine ore grade—the metal content of an ore. • If the ore grade is high enough and the deposit extensive enough, the cost to open a mine may be warranted.
Subsurface mining • Subsurface mining is a mining method in which soil and rocks are removed to reach underlying coal or minerals. • It is used to mine ore deposits that are 50 m or more beneath Earth’s surface. • Room-and-pillar mining is a common method of subsurface mining. This method is used to extract salt and coal. • A network of entries, called rooms, are cut into a seam, a horizontal layer of coal. Between the rooms, pillars of coal are left standing to support the room. When the mining of rooms is complete, the pillars are removed, beginning with the farthest point of the mine.
Longwall Mining • Longwall mining is a more efficient method of removing coal from a subsurface seam. • A machine called a shearer moves back and forth along the face of a coal seam. • As coal is sheared from the long wall, it falls onto a conveyor and is transported out of the mine. • The miners and their equipment are protected by a row of hydraulic roof supports.
Solution Mining • Solution mining is an economical method to mine for deposits of soluble mineral ores, such as potash, salt, and sulfur. • Solution mining dissolves the ore by injecting it with hot water. • Compressed air is then pumped into the dissolved ore, and air bubbles lift it to the surface.
Surface Mining • Surface miningis a mining method in which soil and rocks are removed to reach underlying coal or minerals. • Surface mining methods are used when ore deposits are located close to Earth’s surface. • Large quantities of near-surface ores, like coal, gold, and copper are minedwithopen-pit mining.
Surface Mining • In open-pit mining, ores are mined downward, layer by layer. • Explosive are used, if needed, to break up the ore, before it is hauled out by trucks. • Some ores, like gold, are taken to heap leaching pads, to be extracted with chemicals.
Surface Coal Mining • Coal is mined in several steps on the surface. • The soil covering the area to be mined is removed and set aside. • The overburden, or rock covering the coal, is removed with heavy equipment and piled alongside the cut. • Loaders enter the pit and remove the exposed coal seam. • The pit is refilled with the overburden and contoured. • The soil is laid on top of the overburden.
Quarrying • Open pits, called quarries, are used to mine near-surface materials such as building stone, crushed rock, sand, and gravel. • Aggregates, which are sand, gravel, and crushed rock, are the principal commodities produced by quarrying. • Quarries also produce large quantities of clay, gypsum, and talc.
Solar Evaporation • The solar evaporation process consists of placing sea water, which is about 2.7% sodium chloride, into enormous shallow ponds. • The sun evaporates the sea water, which causes the sodium chloride concentration to increase. • Crystalline salt, or halite, forms when the sodium chloride concentration reaches a little over 25%. • Evaporation is continued until a layer of desired thickness is reached, and the salt is harvested.
Solar Evaporation • About 30% of the world’s salt comes from the solar evaporation process. • This method is used for salt production in areas that receive little rainfall but have high evaporation rates. • Solar evaporation is practical in places such as along the Mediterranean Sea, on San Francisco Bay, and in Australia because evaporation exceeds rainfall.
Placer Mining • Placer deposits are deposits that contain valuable minerals that have been concentrated by mechanical action. • Stream placers are the most important placers. Streams transport mineral grains to a point where they fall to the streambed and are concentrated. • Placer deposits may also from along coastlines by heavy minerals that wash down to the ocean in streams. These heavy minerals are concentrated by wave action.
Placer Mining • Placer gold, diamonds, and heavy minerals are mined by dredging. • A dredge consists of a floating barge on which buckets fixed on a conveyer are used to excavate sediments in front of the dredge. • The heavy minerals are separated from the sediments within the dredge housing. The processed sediments are then discharged via a conveyor located behind the dredge.
Smelting • Smeltingis is the melting or fusing of ore in order to separate impurities from pure metal • It is a process in which crushed ores are melted at high temperatures in furnaces to separate impurities from molten metal. • In the furnace, material called a flux bonds with impurities and separates them from the molten metal. The molten metal, which is desired, falls to the bottom of the furnace and is recovered. • The flux and impurities, which are less dense, form a layer of slag on top of the molten metal.
Undersea Mining • The ocean floor contains significant mineral resources, which include diamonds, precious metals such as gold and silver, mineral ores, and sand and gravel. • Since the late 1950s, several attempts have been made to mine the ocean, with varying degrees of success. • Competition with land-based companies that can mine minerals more cheaply and the great water depths at which some mineral deposits are found are two of the reasons undersea mining has been largely unsuccessful to date.
Objectives • Describeseven important potential environmental consequences of mining. • Namefour federal laws that relate to mining and reclaiming mined land. • Definethe term reclamation. • Describetwo ways in which state governments regulate mining.
The Environmental Impacts of Mining • Because of the potential environmental impact of mining on a large scale, mining is one of the most heavily regulated industries in the U.S. • Mining companies spend large amounts of money to preserve the environment. • Reclaiming the land, or returning land to its original condition after mining is completed, is now a part of every surface mining coal operation.
Air and Noise Pollution • Most surface mines are not located near urban populations because of air and noise pollution. • Noise is created by equipment and by blasting. While noise may be a nuisance, blasting can cause physical damage to nearby structures. • Large amounts of dust are produced by all aspects of mining. • Regulations in the U.S. forbid mining operations to allow dust or noise to exit an area that is being mined.
Water Contamination • Water resources can be negatively impacted by mining. Water that seeps through mine sites can pick up or dissolve toxic substances. • These contaminants can wash into streams, where they can harm or kill aquatic life. • The sulfur in coal can react with oxygen and water to produce sulfuric acid, which can dissolve toxic minerals that remain in mines and excess rock. • Mining regulations in the U.S. requires companies to dispose of acid-producing rock in such a way that water is not contaminated.
Displacement of Wildlife • Removing soil from a surface mine site strips away all plant life. With their natural habitat removed, animals will leave the area. • A good development plan to reclaim a mine site can ensure that the displacement of wildlife is temporary. • Dredging a river disturbs river bottoms and destroys aquatic life. • The disturbance of a river bed can cause muddy sediments to contaminate a river for up to 10 km.
Erosion and Sedimentation • Excess rock from mines is sometimes dumped into large piles called dumps. • Running water erodes unprotected dumps and transports sediments into nearby streams. • These sediments may choke streams and damage water quality and aquatic life.
Soil Degradation • Soil at a mine site is removed from the uppermost layer downward. • When this soil is stored for later reuse, care must be taken to ensure that the upper soil layers are not buried beneath soil layers that were originally below them. • In this way, the soil layers that are richest in important nutrients are not covered.
Subsidence • Subsidence is the sinking of regions of the ground with little or no horizontal movement. • Subsidence occurs when pillars that have been left standing in mines collapse or the mine roof or floor fails. • The locations of many abandoned mines are unknown. Buildings, houses, roads, bridges, underground pipelines, and utilities that are built over these mines could be damaged if the ground below them subsides.
Underground Mine Fires • Fires that start in underground coal seams are one of the most serious environmental consequences of coal mining. • Lightning, forest fires, and burning trash can all cause coal-seam fires. Fires can also start when minerals in the coal that contain sulfur are exposed to oxygen. • These fires are hard to put out and may be left to burn themselves out, which may take decades or even centuries. • Underground fires that burn their way to the surface release smoke and gases that can cause respiratory problems
Mining Regulation and Reclamation • Mines on land in the United States are regulated by federal and state laws. • For example, mining companies must comply with the Clean Water Act and the Safe Drinking Water Act. • Mining operations must also comply with the Endangered Species Act, which ensures that mining activities will not affect threatened or endangered species and their habitats.
Reclamation • Reclamation is the process of returning land to its original condition after mining is completed. • The Surface Mining Control and Reclamation Act of 1977 created a program for the regulation of surface coal mining on public and private land. • The SMCRA also established a fund that is used to reclaim land and water resources that have been adversely affected by past coal-mining activities.
State Regulation of Mining • Mining companies must obtain permits from state environmental agencies before mining a site. • State agencies are also responsible for inspecting mines to ensure compliance with environmental regulations. • Agencies issue violations to companies that do not comply with environmental regulations and assess fines for noncompliance.
