Geology and Nonrenewable Minerals

1. Geology and Nonrenewable Minerals By Danya, Kimmy, and Porter

2. Case Study • General Mining Law of 1872 • Made to encourage exploration and mining and develop the West • Earn rights to mine the land if you pay to maintain it • Modified in 1992 – requires mining companies to post bonds to cover full cost of clean up in case they go bankrupt • Mining companies don’t like • Environmentalists want stricter cleanup requirements

3. Key Concepts • Earth’s major geological processes • Rocks and rock cycles • Finding and extracting mineral resources • Harmful environmental effects • Limited supply of mineral resources

4. Geological Processes • Geology – science devoted to the study of dynamic processes occurring on Earth’s surface and in its interior • Surface and interior are constantly changing (slowly on a human time scale) • Energy from sun, Earth’s interior, and flowing water create continents, mountains, valleys, plains, and ocean basins

5. Earth’s Structure • Three Zones: • Core – innermost zone, intensely hot, solid inner part surrounded by liquid core of molten material • Mantle – thick, solid zone surrounding the core, mostly solid rock but has an asthenosphere of partly melted rock • Crust – outermost and thinnest layer, consists of continental crust (underlies the continents) and oceanic crust (under ocean basins)

6. Internal and External Geologic Processes • Tectonic plates – various sized areas of Earth’s lithosphere that move slowly around the asthenosphere • 15 plates • Move at about the rate at which fingernails grow • Plates colliding, breaking apart and sliding form mountains, ridges, and trenches • Theory of plate tectonics

7. Types of Boundaries • Divergent plate boundary – plates move in opposite directions • Convergent plate boundary – plates pushed together • Subduction – an oceanic and continental plate collide, oceanic plate is denser so it sinks below continental plate at subduction zone • Trenches form at boundaries between two converging plates • Transform fault – plates slide and grind past one another along a fracture in the lithosphere

8. Processes on Earth’s Surface • External processes – changes that occur from energy from sun and gravity • Erosion – material is dissolved, loosened, or worn away from one part of Earth’s surface and deposited elsewhere • Weathering – physical, chemical, biological processes that break down rocks and minerals into smaller pieces that can be eroded • Physical or mechanical weathering – large rock broken into smaller fragments (ex. Frost wedging) • Chemical weathering – chemicals decompose a mass of rock • Biological weathering – conversion of rock/minerals into smaller pieces through action of living things (ex. Lichens)

9. Rocks and Rock Cycles • Mineral – element or inorganic compound that occurs naturally and is solid with a regular internal crystalline structure (ex. Salt, mica, quartz, diamond) • Rock – solid combination of one or more minerals that is part of Earth’s crust (ex. Limestone, quartzite)

10. Rock Types and the Rock Cycle • Igneous rock – forms below or on Earth’s surface when magma wells up from upper mantle and cools (Ex. Granite) • Sedimentary rock – forms from sediment when existing rocks are weathered and eroded into small pieces and transported by water, wind, or gravity. This builds up over time and pressure and dissolved minerals binds the sediments together. • Metamorphic rock – preexisting rock is subjected to high temperature, pressure, or chemically active fluids that change the properties and appearance of the rock • Rock cycle – interaction of physical and chemical processes that change rocks from one type to another

11. Nonrenewable Mineral Resources • Nonrenewable mineral resources – a concentration of naturally occurring material in or on the earth’s crust that can be extracted and processed into useful materials at an affordable cost -Metallic Mineral Resources (iron, copper, aluminum) -Nonmetallic Mineral Resources (salt, clay, sand, phosphate, soil) -Energy Resources (coal, oil, natural gas, uranium) • Ore – rock containing one or more metallic minerals to be mined profitably

12. 4 Categories of Nonrenewable Mineral Resources • Identified Resources (location, quantity, and quality known) • Undiscovered Resources (assumed to exist but location and quality unknown) • Reserves (identified resources from which a usable nonrenewable mineral can be extracted profitably at current prices) • Other Resources (undiscovered resources and resources not classified as reserves)

13. Identifying Promising Mineral Deposits(By Air) • Aerial photos and satellite images that reveal protruding rock formations (outcrops) associated with certain minerals • Planes equipped with… • Radiation-measuring equipment to detect radioactive minerals • Magnometer to find magnetic minerals • Gravimeter to measure differences in gravity produced by differences in density between an ore deposit and the surrounding rock

14. Identifying Promising Mineral Deposits(On the Ground) • Drilling a deep well and extracting core samples • Seismic surveys • Chemical analysis of water and plants

15. Removing Mineral Deposits • Shallow mineral deposits are removed by surface mining • Removing soil, subsoil, and other strata and then extracting a mineral deposit found fairly close to the earth’s surface • Deep deposits are removed by subsurface mining • Extraction of a metal ore or fuel resource such as coal from a deep underground deposit

16. Surface Mining • Mechanized equipment strips away the overburden (layer of soil and rock overlying a mineral deposit) • Discards it as waste material called spoils • Extracts about 90% of the nonfuel mineral and rock resources and 60% of the coal used in the U.S.

17. Types of Surface Mining • Open-pit mining – machines dig holes and remove ores, sand, gravel, and stone • Area strip mining (used where terrain is flat) – an earthmover strips away the overburden, and a power shovel digs a cut to remove the mineral deposit. The trench is then filled with overburden, and a new cut is made parallel to the previous one. • Mountaintop removal – uses explosives, massive shovels, and even larger machinery called draglines to remove the top of a mountain to expose seams of coal underneath a mountain • Contour strip mining (used on hilly or mountainous terrain) – a power shovel cuts a series of terraces into the side of the hill. An earthmover removes the overburden, and a power shovel extracts the coal.

18. Subsurface Mining Pros and Cons • Pros – disturbs less than 1/10 as much land as surface mining and often produces less waste material • Cons – leaves much of the resource in the ground and is more dangerous and expensive than surface mining (cave-ins, explosions, diseases)

19. Environmental Problems With Mining • Scarring and disruption of the land surface • Subsidence (collapse of land above underground mines) • Toxin-laced mining wastes blown or deposited elsewhere by wind or water erosion • Acid mining drainage • Mining has polluted about 40% of Western watersheds • Emission of toxic chemicals into the air • Wildlife exposed to toxic mining wastes when they leak from holding ponds

20. Life Cycle of a Metal Resource Surface mining > metal ore > separation of ore from gangue > smelting > melting metal > conversion to product (sometimes recycled) > discarding of product

21. Environmental Impacts of Mining Ore • Environmental impacts of mining an ore are affected by its percentage of metal content (grade) • More accessible, higher-grade ores used first • Gradually takes more time, money , energy, water, and other materials for lower-grade • Right now, it does not cost companies/consumers much • Full-cost pricing (proposed by environmentalists and economists) includes the cost of environmental harm done in the price of goods made from minerals

22. Supply of nonrenewable minerals: • Depends on: actual/potential supply of minerals and the rate we use it • Economically depleted: when it costs more to find, extract, transport, process remaining deposit than mineral is worth • Five choices: recycle/reuse, waste less, find substitute, do without

23. Depletion • Depletion time: how long it takes to use up certain proportion (80%) of reserves of mineral • Short depletion time assumes no recycling, reuse, or increase in reserves • Longer depletion assumes recycling, reuse, and increase in reserves

24. Economics and Politics • Standard economic theory says in competitive free market plentiful mineral resource is cheap when supply exceeds demand • No longer applies very well in developed countries • In US, mining companies get depletion allowances amounting to 5-22% of gross income • Hardrock mining companies can buy public land at 1872 prices and pay no royalties to government • b/w 1982-2004 US mining companies had $6 billion in government subsidies. • In 1900 the average copper ore=5% copper, and now=.5% and copper costs less

25. Mining Lower-Grade Ores • Limiting factors: increased cost of mining and processing larger volumes of ore, availability of fresh water, environmental impacts of land disruption • To improve mining technology use microorganisms for in-place mining (removes desired metals without disturbing surroundings) also reduces air pollution • Once ore deposit is located, wells are drilled and the ore is fractured • Then ore is inoculated with bacteria to extract desired metal • The well is flooded with water then pumped to surface

26. Cont. • Currently more than 30% of all copper produced (more than $1 billion per year) comes from biomining • However: processing is slow, it can take decades to remove same amount of material that takes other methods only months/years

27. Science Case Study • Nanotechnology: uses science and engineering at atomic/molecular levels to build materials with specified properties • Uses abundant atoms (carbon, oxygen, hydrogen) • Molecular economy: possible way of the future • Because particles get smaller, they also become more reactive/potentially toxic • Can also breach some natural defenses in our bodies • Buckyballs (soccer ball-shaped forms of carbon) caused brain damage to fish within 48 hours

28. Minerals from the Ocean • Only magnesium, bromine, sodium chloride are abundant enough to be extracted profitably from seawater • Deposits of minerals on continental shelf: sand, gravel, phosphates, sulfur, tin, copper, iron, tungsten, silver, titanium, platinum, diamonds • Manganese-fich nodules: found on deep-ocean floor • Might be sucked up by giant vacuum pipes or scooped up by buckets • Have not been developed yet because of increased cost and squabbles over ownership/distribution of profits • Could cause less environmental harm than land mining

29. Finding Substitutes • Materials revolution: silicon/new materials (ceramics and plastics) are being developed as replacements • Ceramics re: harder, lighter, stronger, longer lasting/ can withstand intense heat • Plastics and composite materials are being used in auto and aerospace industries • Cost less to produce, can be molded, don’t need paint

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