Mining Methods and Environmental Issues in Developing Nations

1. Mining Methods and Environmental Issues in Developing Nations

2. Mineral Deposits vs. Ores • A mineral deposit is a naturally-occurring concentration of a particular mineral - examples? • An ore is a mineral deposit that can be economically developed

3. Mineral Deposits vs. Ores • One judge of ore quality is the Concentration Factor • CF = Chost rock/Caverage crust • Other judges of ore quality include location, economic variables, political variables, extraction technology, and environmental variables.

5. World Distribution of Mineral Resources • Generally uneven - determined by geologic history and tectonic setting • High metal concentrations along active or extinct plate boundaries (American Cordillera) • A relatively small population in the industrialized countries now consume the vast majority of the world’s mineral resources, BUT the resources come from ALL nations.

6. Formation of Mineral Deposits • Igneous • gravitational settling of early, dense minerals on floor of magma chamber • e.g. Bushveld Intrusion, South Africa

7. Layers of chromite and platinum in the Bushveld Intrusion, South Africa

8. Formation of Mineral Deposits • Metamorphic • country rocks around an igneous intrusion are changed by heat and chemical reactions with hydrothermal fluids • contact aureole

9. Formation of Mineral Deposits • Hydrothermal • minerals precipitate from hydrothermal solutions above intrusions, leaving veins or disseminated deposits • Porphyry Copper Deposits, such as Bingham Canyon, Utah

10. Porphyry Copper Deposits Bingham Canyon Copper

11. Formation of Mineral Deposits • Sedimentary • Preferential settling of denser minerals from flowing water • Placer deposits: glacial deposit containing particles of valuable mineral • gold placer deposits of California • placer diamond deposits of South Africa

12. Gold Placer Deposits An overview of an example of a gold mining operation supplied by airplane.

13. Gold Placer Deposits

14. Formation of Mineral Deposits • Weathering • removes soluble components of rock, leaving behind concentrated ore • Bauxite aluminum ore in the tropics

15. Formation of Mineral Deposits • Evaporation • leaves a precipitated salt layer • Middle-East Seas • desert lakes world-wide. Saltworks in San Francisco Bay

17. Formation of Mineral Deposits • Secondary enrichment • primary deposit is further concentrated by groundwater dissolution followed by re-precipitation • Copper deposits of Arizona.

18. Mining Methods • Surface Mining • Responsible for 2/3 of world annual mineral production • Open-pits, strip mines, quarries • Employs enormous equipment • Reclamation is expensive and sometimes fails Coal mine, Mpumalanga Province, South Africa

19. Mining Methods • Underground Mining • Cheaper reclamation, but overall more expensive • Less productive than surface mining • Generally more dangerous to miners • Potentially less wasteful than surface mining • Depth limited to about 4 km by high pressures

20. Underground Mining

21. Underground Mining

22. 4-stage evolution of a Producing Mine • Exploration • Evaluation • Development • Production The first 3 may continue after production starts

23. Day to Day Activities at a Working Mine • Expose the ore • Transport and stockpile the ore

24. Day to Day Activities at a Working Mine • Dress the ore • Includes crushing and concentrating the ore before extracting the element of interest • Crushing is done in progressively fine stages

25. Day to Day Activities at a Working Mine • Concentration methods include • Flotation Separation • Gravity Separation using water or heavy liquids • Magnetic Separation

26. Day to Day Activities at a Working Mine • Extractive Metallurgy • Pyrometallurgy (smelting) • Melt concentrate in furnace • Separate metal from slag by distillation or immiscibility • Byproducts include gas, vaporized metals, and dust

27. Day to Day Activities at a Working Mine • Extractive Metallurgy • Hydrometallurgy • Dissolve or leach metal from ore or concentrate • Solvents include sulfuric acid, ammonium, mercury, and sodium cyanide solutions (NaCN dissolves gold) • High-grade ores are vat-leached; low-grade ores are heap-leached • Gold in sulfides is roasted first, creating SO2.

28. Day to Day Activities at a Working Mine • Extractive Metallurgy • Electrometallurgy • Electric current is used to deposit metal on cathodes • Often used to purify metal produced by pyrometallurgy

29. Environmental Issues • Waste Disposal • Amount of waste (tailings) depends on ore grade and extraction technology; can be >99 %. • Finely ground waste rock (tailings) may contain sulfides, heavy metals, and cyanide residue • Underground mines use waste as stope fill • Surface mines convert into slurry and pipe to tailings pond or dump in the ocean

30. Environmental Issues • Problems with Tailings Dams in Developing Countries • Leaks and failures are common • 1988 – China, dam overtopped • 700,000 m3 molybdenum waste released • 20 deaths • 2000 – China, gas explosion • 160 deaths

31. Environmental Issues • Improved engineering of tailings dams in developed countries • Drainage blankets to reduce internal pore pressures • Upstream construction to increase dam strength • Impermeable retention dams • Acid Mine Drainage • Sulfides, a common waste product, react when exposed to the atmosphere to form sulfuric acid

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