Rocks and Minerals Class Notes PDF

Topic 1: Rocks and minerals Topic 1: Rocks and minerals and their exploitation Topic Candidates should be able to: Further guidance and (Learning objectives) exemplification 1.1  describe and interpret t...

Topic 1: Rocks and minerals Topic 1: Rocks and minerals and their exploitation Topic Candidates should be able to: Further guidance and (Learning objectives) exemplification 1.1  describe and interpret the rock cycle  igneous: granite and basalt Formation of rocks  state and explain the formation and  sedimentary: limestone, characteristics of named igneous, sandstone and shale sedimentary and metamorphic rocks  metamorphic: marble and slate 1.2  describe the following methods of  opencast / open-pit / open- Extraction of rocks extraction of rocks and minerals from cut / strip mining and minerals from the Earth:  deep mining / shaft mining the Earth – surface mining  exploration – subsurface mining  geology  discuss the factors that affect the  accessibility decision to extract rocks and minerals  environmental impact assessment  supply and demand 1.3  describe and explain the  loss of habitat Impact of rock and environmental, economic and social  noise, water, land, air, visual mineral extraction impacts of rock and mineral extraction pollution  management of waste  employment opportunities  improvements in local / national economy  improvements in facilities and infrastructure 1.4  describe and evaluate strategies for  safe disposal of mining waste Managing the restoring landscapes damaged by rock  land restoration: soil impact of rock and and mineral extraction improvement, mineral extraction bioremediation, tree planting  making lakes and nature reserves  using as landfill sites 1.5  define sustainable resource and  increased efficiency of the Sustainable use of sustainable development extraction of rocks and rocks and minerals  describe and evaluate strategies for minerals the sustainable use of rocks and  increased efficiency of the minerals use of rocks and minerals  the need to recycle rocks and minerals  legislation Case study:  Study the development, impact and management of a mine including land restoration after the mine has closed. TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 1  Topic 1: Rocks and minerals and their exploitation Formation of rocks Rock is the solid and naturally occurring material that forms the Earth’s hard outer layer or crust. Although rocks come in an incredible variety of shape, size, color, texture, weight, consistency, permeability and hardness, they are almost all composed of an aggregate of grains of different chemical elements called minerals. Rocks are classified according to how they are formed.  Igneous rocks: These rocks are created from the solidification of magma and lava. There are two types of igneous rocks: Intrusive: when magma cools and crystallises slowly within the Earth’s crust (granite). Extrusive: when lava solidifies on the Earth’s surface (basalt).  Sedimentary rocks: Rocks formed by the compression and consolidation of layers of mud, sand, silt and living organisms such as chalk, limestone and clay.  Metamorphic rocks: The Earth’s movements can cause existing igneous and sedimentary rocks to be heated up and put under great pressure. This can cause a chemical change in their minerals and the formation of new metamorphosed rocks (slate from shale / marble from limestone). What do we use rocks and minerals for?  Rocks are the source of all soils that we use to grow food and rear livestock.  Stones and rocks are used for building material.  Rocks do have chemical elements such as lead, aluminium, zinc, copper, uranium etc. which provide industrial metals and fuels.  The decorative beauty of precious stones in jewelry. Rock: The dry, solid and naturally occurring material that forms the Earth’s crust. Crust: The top layer of the Earth, which can be either continental (with land on top) or oceanic. Minerals: A naturally occurring solid and inorganic chemical substance with a crystalline structure found in rock. Magma: Liquid rock found beneath the Earth’s crust. Lava: Hot molten or semi-fluid rock erupted from a volcano. TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 2 The rock cycle The rocks of the Earth’s crust are constantly being changed and recycled. As soon as any ‘new’ rock is exposed to the physical, chemical and biological forces of weathering, it begins to be broken down into sediments. For example: - Physical weathering through exfoliation causes the surface layers of rocks to disintegrate as a results of constantly being heated and cooled. - Rainwater containing dissolved CO2 will remove limestone rock particles (chemical weathering). - The roots of trees and plants will over time pull apart joints and cracks in rocks and cause biological weathering as they search for water. Sediments of all sizes is transported away by wind and water erosion and can be deposited a long way from where they originated. If sediments accumulate in hollows beneath seas and oceans then sedimentation begins, which in time will create new sedimentary rocks. If these rocks become buried deep inside the Earth, then a combination of heat and pressure can change them into metamorphic rocks – or they might even melt entirely to become magma. The magma may solidify below the surface or above ground as lava to form new igneous rock, which will immediately come under attack once again from the forces of weathering. Weathering: The breakdown of rocks by physical, chemical and organic (biological) processes with little or no transportation of the resulting rock particles. Erosion: The wearing away of the land by an agent such as water that carries away the rock particles. TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 3 Extraction of rocks and minerals from the Earth There are two main methods of extracting rocks containing minerals from the Earth’s crust: Surface mining and subsurface mining. Surface mining: This approach can only be used when the rocks containing the mineral (the ore body) are found relatively close to the surface and the surrounding area is not heavily built up. The soil and rock overlying the ore body (called the overburden) is first removed by specialist earth- moving heavy machinery. Once exposed, other equipment such as massive dragline and bucket wheel excavators dig out and remove the ore body from flat terraces or benches that circle the mine at descending levels. Subsurface mining: Subsurface mining removes the minerals through underground mining methods such as declines, vertical shafts, and tunnels, and adits. The overlaying rocks remain in place. Declines are wide tunnels that descends in a circular manner down to and around the ore body. The ore is hauled to the surface in huge trucks. When the ore body is too deep to be reached by inclines, tunnels are sunk down adjacent to the ore body, which is then removed by lifts. Adits are horizontal rather than vertical shafts excavated into the side of a hill or mountain following level layer of ore. (adit mine) TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 4  Mine type Advantages Disadvantages Surface: Easier access to materials. Large areas of land damaged, looks Open pit Large size of mines allow easy access unsightly, and causes a lot of dust and noise mining of machines and workers. pollution. Produces large amounts of waste rock (spoil). Surface: Easy access to the seams of minerals Impacts large areas of land. Causes a lot of Strip (from the surface). Large machines cut dust and noise pollution. mining into the edge of the seam removing Large amounts of spoil (waste rock). minerals efficiently and quickly. Sub- Access to seams from sloping tunnel More technically complex than strip or open surface: (adit) means less costly than making cast mining (there is a risk of tunnel Drift shafts. Majority of overburden left in collapse). mining place. (Adits) Sub- Reaches minerals not accessible by Most expensive method. Risk of tunnel/shaft surface: other methods. collapse, poisonous gases, underground fires Shaft Less impact of the surface ecosystem and explosions. mining (although still produces waste heaps). Surveying techniques used to determine the geology of the underlying rock. If a mining company has no existing knowledge of mineral deposits in an area, but believes that potential ore bodies may be present underground, it may begin the process of mineral ‘greenfield’ exploration. A number of surveying techniques are then commonly used to determine the underlying rock and identify patterns indicative of certain mineral deposits. - Detecting radiation: The use of radioactivity in geologic studies is based on the presence in rocks of the radioactive elements uranium and thorium, and a radioactive isotope of potassium. These elements and their isotopes emit gamma rays that can be detected with instruments such as electrometers and spectrometers. - Measuring magnetism: To discover the presence of concealed deposits, magnetic surveys are usually conducted on the surface of the Earth. Many ore minerals have higher density than the surrounding rocks. By measuring variations in the Earth’s gravity field over an area, an indication of the nature of the underlying geology and the likely presence of deposits can be obtained. - Remote sensing: satellite imagery combined with geological seismic mapping using artificially created shock waves. TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 5 Factors affecting the mining of rocks and minerals:  Expenses: The cost of exploration (and extraction).  Geology: can the ore be extracted cheaply by open cast methods or will more expensive underground tunnels be required.  Climate: location suitable for mining because of climatic factors.  Environmental impact: Environmental impact assessment must be undertaken to determine the impact on the environment.  Supply and demand: relationship between how much of a mineral/ore is available and how much is needed the consumers.  The location suitable for mining: The more remote and hostile the environment , the higher the costs will be in overcoming problems, for example, building transport and communication links, creating water and power supplies and constructing houses for employees. Impact of rock and mineral extraction: Economic impacts: (positive)  Multiplier effect: When a mine is opened it does not only create a job at the mines, but it also creates other jobs in companies supplying the mines, for example with machinery or services such catering, cleaning and security.  Trickledown effect: The workers of the mine spend their wages buying products and services in the local community, which helps to create further jobs, for example, in restaurants or sport centres etc. Environmental Impacts: (negatives)  Habitat and biodiversity loss: The clearing of huge areas of land for the mine, can cause catastrophic decline in the range of plants, trees, birds and animals.  Water pollution: water is contaminated with heavy metals such as mercury and lead, this is known as acid rock drainage. This water can run off the surface into nearby rivers or seep underground until it reaches the water table.  Air; noise and visual pollution: The excavation, crushing and refining of mineral ore can release huge quantities of dust containing dangerous heavy metals such as lead into the atmosphere. Visually, mining operations can be very disturbing. They are huge and noisy complexes, operating 24 hours a day, all year round.  Soil erosion and sedimentation: Once soil has been disturbed to make way for mining operations, it can be very quickly eroded by rainfall and the wind. Soil can be carried into the rivers by rainwater, where sedimentation leads to a shallowing of the river. TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 6 Managing the impact of rock and mineral extraction: How can the mined land be returned to an environmentally acceptable standard?  The most common method is to fill the hole with the waste heaps or with landfill. Add fertilizers, plant grass and create an environmentally friendly environment. Other methods include:  Remediation: Making it safe by demolishing industrial plant, removing machinery, stabilizing the ground, draining the pipelines and disposing of toxic waste. Two methods of remediation:  Tailing ponds for mineral waste Tailings consist of finely ground particles of rocks and minerals that result from ore processing and contains poisonous chemicals such as arsenic. They are usually mixed with water and disposed of in tailing ponds. The contaminated water is often dealt with at water treatment plants set up on site.  Bioremediation A process in which living things are used to remove toxic chemicals from a natural site. Some microorganisms, such as bacteria found in the soils, are able to absorb pollutants and process them into less harmful substances.  Restoration: Returning the land to its original condition. Many mining sites are returned to their pre-mine use, which in the majority of cases is open countryside. Care is taken to rebuild the ecosystem, planting native trees and plants. Nature reserves may also be created, incorporating lakes from open-pit mines.  Reclamation/reuse: Use the decommissioned (old) mine for another use, so they continue to economically contribute to the local community. Examples: aquaculture, ecotourism, farming or even commercial forestry. TOPIC 1: ROCKS AND MINERALS AND THEIR EXPLOITATION 7 Sustainable use of rocks and minerals Sustainable development: The development of technology and the environment to meet increasing human needs and living standards without impacting negatively on the ecosystems.  How can we extend the life of mineral ores? - Use of modern technology to extract minerals more efficiently from ore bodies that previously were not economical to exploit, and also from waste rock and tailings at existing mines. - Substitute the use of scarce minerals with more common minerals or non-mineral alternatives. - Recover minerals through recycling of discarded products. - Laws and regulations to encourage the efficient use of minerals. Conservation.  Increasing the availability of minerals reserves: - The search to discover new mineral reserves through seismic waves, remote sensing and geochemistry, is being carried out by mining corporations all over the world. 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