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Environmental Science Geology 1401410 Instructor: Dr. Thieme

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Ore - a rock that contains a large enough concentration of a particular mineral ... Abandoned Copper Mine Shaft at Ducktown, North Carolina (a shaft mine) ... – PowerPoint PPT presentation

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Title: Environmental Science Geology 1401410 Instructor: Dr. Thieme


1
Environmental ScienceGeology 1401-410Instructor
Dr. Thieme
  • 16th Lecture Rocks, Minerals,
  • and Mineral Resources

2
Definition of a Mineral
  • naturally occurring
  • inorganic
  • solid
  • crystalline (orderly internal structure)
  • definite chemical composition

3
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.
4
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.
7
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

11
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

12
Detrital Sedimentary Rocks
13
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

16
Metamorphism
  • Type
  • Contact (thermal)
  • Hydrothermal
  • Regional
  • Impact
  • Grade (from Low to High)

17
Contact Metamorphism
18
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

19
Mid-Atlantic Ridge
20
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
23
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

24
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

25
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.

28
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)

29
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"

33
Contact Metamorphic
At the Cornwall mine in Pennsylvania,
iron-rich fluids from an intrusive Triassic
diabase replaced part of a limestone bed with
magnetite.
34
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
35
Regional Compression
36
Hydrothermal
Porphyry Copper Deposits are among the richest
ores of hydrothermal origins. The metal is found
in tiny fractures.
37
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.
38
Placer
  • sedimentary layer in which metal ore minerals are
    concentrated and from which they can be separated
    by density
  • gold, ilmenite, rutile, hematite

39
Residuum ("Brown Ores")
  • laterite - old tropical soils with hematite,
    goethite, siderite
  • bauxite - ore of aluminum

40
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

41
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

42
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

43
Bingham Canyon mine near Salt Lake City, Utah is
the largest man-made excavation on earth (an
open pit surface mine).
44
Abandoned Copper Mine Shaft at Ducktown, North
Carolina (a shaft mine)
45
Abandoned Diamond Mine Shaft in Kimberly, South
Africa
46
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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