Environmental Science Geology 1401410 Instructor: Dr. Thieme

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Environmental ScienceGeology 1401-410Instructor
Dr. Thieme

• 16th Lecture Rocks, Minerals,
• and Mineral Resources

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Definition of a Mineral

• naturally occurring
• inorganic
• solid
• crystalline (orderly internal structure)
• definite chemical composition

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Mafic minerals or rocks are those whose
composition is enriched in magnesium and iron
(Fe). Felsic minerals or rocks are those which
have the composition of feldspars or abundant
silica.
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Rocks, Ores, and Metals

• Rocks are naturally formed aggregates, or
  mixtures, of minerals and have varied chemical
  compositions
• Ore - a rock that contains a large enough
  concentration of a particular mineral that the
  mineral can be profitably extracted
• Metal - an element such as Fe, Al, Cu, Ag, Au...
  which is malleable, lustrous, and a good
  conductor of heat and electricity

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Igneous Rocks - crystallized from magma which
either intruded deep beneath the surface
("plutonic") or extruded to the surface
("volcanic") Sediment - particles and dissolved
substances which settle out of a liquid (oceans,
river floodplains, swamps), also windblown
(dunes) Sedimentary Rocks - sediment compacted
by weight of overlying layers, cemented by
percolating water, or chemically
precipitated. Metamorphic Rocks - Igneous rocks,
sediment, or sedimentary rocks altered by being
subjected to temperature or pressure conditions
above those at the Earth's surface.
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Igneous Rocks

• Plutonic or Intrusive Igneous Rocks crystallize
  at depth. The crystals may be up to a meter long
  and take tens to hundreds of thousands of years
  to form (phaneritic texture).
• Volcanic or Extrusive Igneous Rocks erupt at the
  surface. Because they crystallize rapidly, the
  individual minerals are so small that they can
  only be distinguished with the aid of a
  microscope (aphanitic texture).

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Sedimentary Rocks

• Sediment originates from mechanical and/or
  chemical weathering
• Rock types are based on the source of the
  material
• Detrital rocks transported sediment as solid
  particles
• Chemical rocks sediment that was once in
  solution
• Pyroclastic rocks - formed during volcanic
  eruptions

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Detrital sedimentary rocks

• The chief constituents of detrital rocks include
• Clay minerals
• Quartz
• Feldspars
• Micas
• Particle size is used to distinguish among the
  various types of detrital rocks

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Detrital Sedimentary Rocks
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Chemical Sedimentary Rocks
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Metamorphism

• The transition of one rock into another by
  temperatures and/or pressures unlike those in
  which it formed
• Metamorphic rocks are produced from
• Igneous rocks
• Sedimentary rocks
• Other metamorphic rocks

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Metamorphism

• Type
• Contact (thermal)
• Hydrothermal
• Regional
• Impact
• Grade (from Low to High)

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Contact Metamorphism
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Hydrothermal Metamorphism

• Chemical alteration caused when hot, ion-rich
  fluids, called hydrothermal solutions, circulate
  through fissures and cracks that develop in rock
• Most widespread along the axis of the mid-ocean
  ridge system

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Mid-Atlantic Ridge
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Regional Metamorphism

• Produces the greatest quantity of metamorphic
  rock
• Associated with mountain building ("orogenesis")
  in convergent margin plate tectonic settings

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Oceanic-Continental Plate Convergence
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Subduction Zones

• Mountainous terrain adjacent to subduction zones
  exhibit distinct linear belts of metamorphic
  rocks
• High-pressure, low-temperature zones nearest the
  trench
• High-temperature, low-pressure zones further
  inland in the region of igneous activity

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Continent-Continent Plate Collisions

• Compressional stresses deform the edges of the
  plate
• Formation of the Earths major mountain belts
  including the Alps, Himalayas, and Appalachians

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LOW GRADE
HIGH GRADE
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Earth Materials as Resources

• Earth resources are determined by geology in the
  first place
• mineralogy - the form in which a metal or other
  valued substance is held
• grade - the proportion of that substance found in
  a given deposit
• Extent of reserves or ores depends on technical
  means of extraction.

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Metals

• opaque (i.e. mafic as opposed to felsic)
• tough (i.e. hardness gt 5)
• ductile, malleable, or fusible (at high T)
• conductors of heat and electricity
• Mg, Al, Si, Ti, Mn, and Fe are abundant
• Au, Ag, Pt, Pd, Rh, Ir, Os, and Ru are precious
  (gold, silver, and the platinum group)

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Abundant Metals
Abundance is here the estimated percent of the
Earth's crust, by weight.
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Types of Resource

• Fresh mantle intrusions contains Fe and other
  metal elements
• New minerals formed by metamorphism also often
  contain metals
• Hot water precipitates gold, silver, and other
  ores (hydrothermal fluids)
• Diagenesis (burial and low-temperature
  alteration) of sediments and organic matter
  generate hydrocarbons and other "fossil fuels"

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Contact Metamorphic
At the Cornwall mine in Pennsylvania,
iron-rich fluids from an intrusive Triassic
diabase replaced part of a limestone bed with
magnetite.
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Impact Metamorphic
The largest reserves of nickel in the world are
in the Sudbury district, Ontario, where the
intrusions form a ring structure, triggered by
the impact of an extraterrestrial object
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Regional Compression
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Hydrothermal
Porphyry Copper Deposits are among the richest
ores of hydrothermal origins. The metal is found
in tiny fractures.
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Diagenic
The richest lead-zinc deposits in the
United States are formed by the expulsion
of metal-bearing fluids from shales
with subsequent deposition in the limestones
on the flanks of the Mississippi
Valley sedimentary basin.
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Placer

• sedimentary layer in which metal ore minerals are
  concentrated and from which they can be separated
  by density
• gold, ilmenite, rutile, hematite

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Residuum ("Brown Ores")

• laterite - old tropical soils with hematite,
  goethite, siderite
• bauxite - ore of aluminum

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Extracting Minerals

• whether surface or subsurface mining can be used
  is determined by the depth of the deposit
• Surface Mining is typically less expensive,
  depending on the thickness and composition of the
  overburden
• Subsurface Mining disturbs the land less, but is
  more expensive and more hazardous for miners

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Surface Mining

• Open-Pit Surface Mining is usually used for iron,
  copper, stone and gravel
• Strip Mining is where the overburden is placed in
  a trench alongside the trench from which the
  metal ore or coal is being removed

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Subsurface Mines

• Shaft Mines are excavated vertically to the ore,
  which is then broken up and hoisted through the
  shaft
• Slope Mines have slanting passages through which
  the ore can be hauled up in cars

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Bingham Canyon mine near Salt Lake City, Utah is
the largest man-made excavation on earth (an
open pit surface mine).
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Abandoned Copper Mine Shaft at Ducktown, North
Carolina (a shaft mine)
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Abandoned Diamond Mine Shaft in Kimberly, South
Africa
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Underground Mines

• favored geologically by
• vertical thickness of ore bodies
• horizontal extent of ores
• roof rock stability
• absence of gas or liquid phases in host deposit

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