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Rocks, Minerals, Mining
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Rocks and the Rock Cycle
The rock cycle is the constant formation and destruction of rock The rock cycle recycles scarce minerals and elements
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Rocks Rocks are any solid mass of mineral or mineral-like matter occurring naturally as part of our planet Types of Rocks Igneous rock is formed by the crystallization of molten magma Intrusive form within the earth Extrusive form when magma cools above the earth’s surface
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Rocks Types of Rocks Sedimentary rock is formed from the weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented. Metamorphic rock is formed by the alteration of pre-existing rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids.
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Rock Cycle
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Rock Cycle Energy That Drives the Rock Cycle
Processes driven by heat from the Earth’s interior are responsible for forming both igneous rock and metamorphic rock Weathering and the movement of weathered materials are external processes powered by energy from the sun. External processes produce sedimentary rocks
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Minerals Definition of a Mineral Naturally occurring Solid substance
Orderly crystalline structure Definite chemical composition Generally considered inorganic
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Minerals How Minerals Form Crystallization from magma Precipitation
Pressure and temperature Hydrothermal solutions
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Weathering & erosion
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Physical Weathering The mechanical breakdown of rocks and minerals
Can be caused by: Water, wind, temperature variations Biological agents such as roots Bottom line: more surface area for chemical weathering
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Chemical Weathering Breakdown caused by chemical rxns, and/or dissolving of elements from rocks Can be caused by: Naturally occurring acids Lichens produce acid to break down rock Anthropogenic: acid rain
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Erosion The physical removal of rock fragments (sediment, soil, etc)
A result of 2 mechanisms: Physical: wind, water, ice Biological; burrowing animals Erosion is a natural process
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Distribution of mineral resources
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Surface Mining Strip mining:
Removal of “strips” of soil and rock to expose ore Large volume of material is removed, resource extracted and the tailings are returned
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Surface Mining Open-pit mining:
Creation of a large pit; resource close to sfc, but extends Copper mines Mountaintop removal Uses explosives to remove the entire top of a mountain Tailings are often deposited in lower elevations (rivers and streams)
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Surface Mining Placer Mining
Process of looking for minerals in river sediments California gold rush
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Subsurface Mining If mineral resource is more than 100m below sfc
Begins with horizontal tunnel Vertical shafts are drilled Deepest mines on earth – 3.5 km
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Mining Safety and the Environment
Soil erosion Waterway damage Habitat fragmentation Pollution from tailings Groundwater & stream damage (mountaintop) Placer mining uses toxic metals (Hg) Acid mine drainage (pumped out of tunnels)
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Mining Safety and the Environment
Subsurface mining is dangerous Explosions Accidental burial Fires Respiratory diseases (e.g. black lung disease)
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Mining Legislation Mining Law of 1872
Regulate mining of Ag, Cu, Au ores and fuels on federal lands Written to encourage development and settlement of west Surface Mining Control & Reclamation Act of 1977 Mandate: minimal disturbance of land during mining and reclaimed after
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