Ugrc 140 (earth resources)


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Ugrc 140 (earth resources)

  1. 1. OVERVIEW Purpose and Objectives of lesson Introduction Elements as building blocks What are minerals? Types of mineral deposits Minerals extraction Economic factors in mining Environmental consequence of mining Conclusion 2
  2. 2. Purpose and Objectives This lesson is to enable you understand what minerals/ores are, the various ore deposits and extraction It is expected that by the end of the lesson you should be able to ….. 3
  3. 3. Purpose and Objectives  State the characteristics of minerals  Identify the various formations of minerals  State and explain the types of mineral deposits  Differentiate between metallic and non- metallic minerals  State the mineral extraction methods  Develop the understanding of the environmental problems associated with minerals extraction 4
  4. 4. Introduction There is the understanding of the existence of minerals More detailed knowledge is required to understand the various categories of minerals/deposits and the environmental impact of mining 5
  5. 5. Elements and the Periodic Table Elements are the basic building blocks of minerals Over 100 elements are known
  6. 6. The Periodic Table
  7. 7. What are Minerals 1. Naturally occurring 2. Solid substance 3. Orderly crystalline structure 4. Definite chemical composition 5. Generally considered inorganic
  8. 8. How many minerals are there? About 4000 minerals are listed but relatively few are popular due to their pleasing appearance Generally composed of more than one element or compound
  9. 9. Native ElementsMinerals made up of only one elementE.g. copper, gold, mercury, silver
  10. 10. Formation of minerals Crystallization from magma Precipitation from solution Recrystallization as a result of high pressure and temperature Crystallization from hydrothermal solutions
  11. 11. Minerals formed as a result of Crystallization of Magma
  12. 12. Metallic and non-metallicminerals Metallic If the surface of the mineral reflects light e.g. Copper, Gold, Pyrite, Iron, Aluminum Non-metallic If the surface of the mineral does not reflect light e.g. Sulfur, Halite (rock salt),Feldspar, quartz, calcite
  13. 13. Pyrite (Fool’s Gold) is Metallic
  14. 14. NativeCopper
  15. 15. Rocks They consist of many individual mineral grains firmly held together in a solid mass Types of Rocks Igneous Sedimentary metamorphic
  16. 16. Ore Deposits An ore is a rock in which a valuable mineral or metal occurs at the concentration sufficiently high, relative to average rocks, to make it economically worth mining The value of a mineral or metal extracted and its concentration in a particular deposit are the major factors determining the profitability of mining a specific deposit
  17. 17. Definition of a mineral or rockresourceMineral or rock resources are any material of value that are derived from rocks or minerals
  18. 18. Definition of a mineral or rockresourceThe resources can be separated into threegroups Metallic E.g. gold, platinum, silver, copper, iron, aluminum, tin, lead, uran
  19. 19. Definition of a mineral or rockresourceNon-metallicE.g. diamonds and otherpreciousstones, salt, gypsum, potash
  20. 20. Definition of a mineral or rockresourceRocksE.g. marble, cutgranite, crushed stone, sandand gravel
  21. 21. Mineral Resources Non-metallic Minerals Sulfur, Gypsum, Coal, Barite, Salt, Clay, Feld spar, Gem Minerals, Abrasives, Borax, Lime, Magnesia , Potash, Phosphates, Silica, Fluorite, Asbest os, Mica Metallic Minerals Ferrous: Iron and Steel, Cobalt, Nickel Non – ferrous: Copper, Zinc, Tin, Lead, Aluminum, Titaniu m, Manganese, Magnesium, Mercury, Vana dium, Molybdenum, Tungsten, Silver, Gold, Platinum
  22. 22. Types of Mineral DepositsIgneous rocksand magmatic depositsHydrothermal oresMetamorphic depositsSedimentary deposits
  23. 23. Types of Mineral Deposits Weathering-leaching away of unwanted minerals leaving a residue enriched in some valuable metal Placer -ores concentrated by stream or wave action on the basis of mineral densities or resistance to weatheringAll require a concentration mechanism
  24. 24. Igneous rocks and magmatic deposits Gravity causes early-crystallizing dense minerals to sink to bottom of magma chamber Minerals may also float to the top if they are less dense than magma Chromite, magnetite, and platinum- group mineral deposits often formed in this way
  25. 25. Magmatic segregation
  26. 26. Diamonds Diamonds are formed at very high pressures Usually require 100-200 km depth Brought rapidly to the surface by Kimberlite magmas.  These are gas-rich magmas that explode on their way to the surface. May erupt at very high velocities. Only need a few diamonds per ton of rock to make the rock an ore.
  27. 27. Hydrothermal deposits Hot waters percolating through the rocks surrounding an intrusion leach elements from them Later deposits these elements in minerals that crystallize when the fluids cool as they approach the surface. Often this process forms veins rich in sulfide minerals that contain metals such as Cu, Pb, Zn, Au, Ag, Pt, and U
  28. 28. Mineral-Rich Hot Water Seeps into Rock Fractures
  29. 29. Metamorphic deposits Increasing pressure and temperature creates new minerals, sometimes in great abundance if the composition is right Generally, metamorphism produces concentrations of useful minerals, rather than a concentration of a specific element. Examples include graphite, asbestos, and garnet (abrasive).
  30. 30. Sedimentary Deposits Processesassociated with the formation of sedimentary rocks can also produce economic mineral deposits E.g. Banded iron ores  Iron-rich layers alternating with silicate - or carbonate-rich layers
  31. 31. Sedimentary Deposits Banded iron ores Mode of formation In early earths history, atmosphere was reducing (oxygen poor). In reducing environments iron is soluble in water However, worlds oceans contained more oxygen due to the action of one-celled plants, such as algae
  32. 32. Sedimentary Deposits Banded iron ores Mode of formation Therefore, the oceans were oxidizing In oxidizing environments iron precipitates out of solution So as iron-rich waters entered the oceans the iron precipitated out forming layers of iron- rich sediment and eventually forming rocks
  33. 33. Sedimentary deposits E,g. Evaporites: As seawater evaporates in hot, dry climates dissolved minerals, such as calcite, gypsum and halite, crystallize Form sediment layers (and rocks) rich in these minerals Occurs naturally and also in man-made evaporation ponds
  34. 34. Weathering Intense chemical weathering leaches out most elements Material left behind is enriched in Al and Fe Forms bauxite (the ore for aluminum) in lateritic soils
  35. 35. Placer deposits Dense,heavy minerals fall out of suspension when water velocity decreases Thiscan concentrate a specific mineral in a confined area, and often occurs in streams or in coastal environments
  36. 36. Placer deposits The minerals formed in a particular area are transported, sorted, and concentrated by the water, to form a placer deposit Many gold, tin, and diamond deposits are formed in this way
  37. 37. Placer deposit
  38. 38. Metallic ResourcesAbundant Metals Iron, aluminum, manganese, titanium, silicon, magnesium Produced by variety of geologic processes Supplies for future is adequate Not distributed uniformly
  39. 39. Metallic ResourcesScarce Metals Comprise less than 0.1% of Earth’s crust (rare conditions concentrate them) (e.g. copper, lead, zinc, gold, and silver) Fewer deposits, so supplies are more precarious
  40. 40. End of Lecture 3
  41. 41. Lecture 4 Cont………….
  42. 42. Classification of MineralsCan be classified based on their composition 1. Silicates Silicon and oxygen combine to form a structure called the silicon-oxygen tetrahedron. This silicon-oxygen tetrahedron provides the framework of every silicate mineral.
  43. 43. Classification of Minerals 2. Carbonates Minerals that contain the elements carbon, oxygen, and one or more other metallic elements
  44. 44. Classification of Minerals 3. Oxides  Minerals that contain oxygen and one or more other elements, which are usually metals
  45. 45. Classification of Minerals 4. Sulfates and Sulfides  Minerals that contain the element sulfur
  46. 46. Classification of Minerals 5. Halides  Minerals that contain a halogen ion plus one or more other elements
  47. 47. Classification of Minerals 6. Native elements  Minerals that exist in relatively pure form
  48. 48. Sulfides
  49. 49. Native Copper
  50. 50. Properties of Minerals Streak The color of a mineral in its powdered form
  51. 51. Properties of Minerals Luster Used to describe how light is reflected from the surface of a mineral
  52. 52. Pyrite (Fool’s Gold) Displays Metallic Luster.
  53. 53. Properties of Minerals Crystal form The visible expression of a mineral’s internal arrangement of atoms
  54. 54. Quartz Often Exhibits Good Crystal Form.
  55. 55. Properties of Minerals Hardness Is a measure of the resistance of a mineral to being scratched
  56. 56. Properties of Minerals Mohs scale Consists of 10 minerals arranged from 10 (hardest) to 1 (softest)
  57. 57. Mohs Scale of Hardness
  58. 58. Properties of Minerals Cleavage The tendency of a mineral to cleave, or break, along flat, even surfaces
  59. 59. Mica Has Cleavage in One Direction
  60. 60. Properties of Minerals Fracture Minerals that do not show cleavage when broken are said to fracture Fracture is the uneven breakage of a mineral
  61. 61. Conchoidal Fracture
  62. 62. Properties of MineralsDensityIs a property of all matter and it is the ratio of an object’s mass to its volume
  63. 63. Prospecting, Exploration and Mining Prospecting Exploration MiningThe act of looking for a Involves many different spot where there is methods in looking for spot of mineralization The extraction of the orevaluable ore in order to from such a place mine there Great impact work Very low impact work involved. involved Drilling, trenching, etc. Great impact work also
  64. 64. Prospecting and Exploration Satellite and Aerial  Geochemical Sampling Photography  Electrical Sounding Remote Sensing  Ground-Penetrating Geological Mapping Radar Magnetic Mapping  Seismic Methods Gravity Mapping o Reflection : Detailed Radioactivity Mapping but expensive o Refraction : Cheap but not Detailed  Core Sampling and Well Logging
  65. 65. Mineral extractionMineral resources are typically extractedfrom rocks using a variety of techniques:• Strip mining• Quarrying• tunnel mining• heap-leaching• Flotation• Crushing - treatment by chemicals to extract metal from rock "flour"• Smelting
  66. 66. Economic Factors in Mining Richness of Ore Quantity of Ore Cost of Initial Development Equipment, Excavation, Purchase of Rights Operating Costs: Wages, Taxes, Maintenance, Utilities, Regulation Price of the Product Will Price Go up or down?
  67. 67. Life Cycle of a MineExplorationDevelopmentActive Mining o Excavation o Crushing, Milling, Flotation, Chemical Separation o Smelting and Refining o Disposal of Waste (Tailings)Shut-down
  68. 68. Issues in Mineral ExploitationWho Owns (or should own) minerals?  Landowner,  Discoverer,  GovernmentUnclaimed Areas:  Sea Floor,  AntarcticaWho Controls access for Exploration?o Nobody is obligated to let someone onto their property to prospect. However, they must allow access if someone owns the subsurface rights.
  69. 69. Problems of MiningSafety Environmental Mine Wastes Problems Pollution  Exploration Dust  Construction and Noise OperationSulfur Economic Impact Acid Rain  "Boom and Bust" Acid Runoff Cycles Dissolved Metals (Fe, Cu, Zn, As...)
  70. 70. POSITIVE IMPACT• Creation of Employment• Provide raw materials for the construction Industries• Encourage cottage Industries• Generate income• Earn revenue for the government
  71. 71. Environmental impacts of mineral and rock exploitation Mining is any activity that involves excavating the earth surface for the purpose of exploiting and processing the mineral wealth for economic and industrial development both for local and export markets. This process normally has a negative impact on the environment. There are two main methods of mining;  Underground mining  Open cast mining
  72. 72. Underground Mining This refers to any sub-surface vertical or horizontal excavations that are made for the extraction of minerals. This method has little effect on the vegetation and the ecosystem in general.Open-casting Mining This refers to uncovered excavations made on the ground for the purpose of mineral or rock exploitation such as the open quarries, pits, trenches, etc.
  73. 73. Impact of Mining on theEnvironment Any mining operation draws ores and other raw materials from the earth This has a direct impact on the biological and physical environment The nature and degree of impacts vary widely depending on the location and type of operation.
  74. 74. Impact of Mining on theEnvironment However, mining operations will generally affect the hydrological functions and hence water quality. This is because mining interferes with the ground water table by lowering it and introducing pollutants to the aquifer
  75. 75. Impact of Mining on theEnvironment Effects can either be physically or chemically influenced depending on the mining activities Disturbs land by removing surface vegetation and changing topography Affects hydrological functions and water quality, causes soil erosion and stream sedimentation that cause death of trees along river banks
  76. 76. Impact of Mining on theEnvironment Produces dust Lowers the water tables Destroys wildlife habitat. The additional vehicular traffic around a mine site brings noise and increases wear on the roads.
  77. 77. ACID MINE DRAINAGE Mining activity occurs in areas that have high concentrations of economically important materials, such as gold, silver, copper, cobalt, iron, lead, and zinc These areas may also contain high concentrations of noneconomic elements such as arsenic, selenium, mercury, and sulphur, whose presence is closely tied to
  78. 78. ACID MINE DRAINAGE Many of these economic and noneconomic elements can be hazardous if released into the environment Even without mining, mineralized areas can naturally adversely affect the environment.
  79. 79. ACID MINE DRAINAGE A common process that results in dispersion of elements from a mineralized site is acid rock drainage. When acid drainage results from mining activity, it is more specifically called acid mine drainage. As the name implies, acid mine drainage is the formation and movement of highly acidic water rich in heavy metals
  80. 80. ACID MINE DRAINAGE This acidic water is formed principally through chemical reaction of surface water (rainwater, pond water) and shallow subsurface water with rocks that contain sulphur-bearing minerals (e.g., pyrite), resulting in sulphuric acid.
  81. 81. ACID MINE DRAINAGE Heavy metals can be leached from rocks that come in contact with the acid, a process that may be substantially enhanced by bacterial action. The resulting fluids may be highly toxic and when mixed with groundwater, surface water, and soil may have harmful effects on humans, animals and plants.
  82. 82. ACID MINE DRAINAGE Mining accentuates and accelerates natural processes. The development of underground workings, open pits, ore piles, mill tailings, and spoil heaps and the extractive processing of ores enhance the likelihood of releasing chemical elements to the surrounding area in large amounts and at increased rates relative to unmined areas
  83. 83. ACID MINE DRAINAGE Studies describing both the extent and effect of acid drainage both in unmined mineralized areas and in areas containing inactive and abandoned mines are required if the environmental impact of heavy metals is to be understood. Studies in unmined mineralized areas describe the natural, baseline chemical characteristics and variations of the mineralized areas.
  84. 84. ACID MINE DRAINAGE By combining these baseline studies with information from areas containing inactive and abandoned mines, it is possible to provide:  An assessment of the intensity and extent of environmental impact due to acid mine drainage  An understanding of natural processes to detect and predict where and when acid mine drainage might occur.