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.

4. EARTH: An Introduction to Physical Geology 7th ed / Tarbuck & Lutgens fig 21.2
The annual per capita consumption of nonmetallic and metallic mineral resources for the United States is nearly 10,000 kilograms (11 tons)! About 94 percent of the materials used are nonmetallic. (After U.S. Bureau of Mines)

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
Left: Sample of Merensky Reef showing from top to bottom: feldspathic pyroxenite, top chromite stringer, pegmatoidal feldspathic pyroxenite with sulphides, basal chromite stringer, mottled anorthosite (sample courtesy of Mr Kevin Boerst).

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. Coal mine, Mpumalanga Province, South Africa
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

32. ~ End ~

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