Title: Environmental Science Geology 1401410 Instructor: Dr. Thieme
1Environmental ScienceGeology 1401-410Instructor
Dr. Thieme
- 16th Lecture Rocks, Minerals,
- and Mineral Resources
2Definition of a Mineral
- naturally occurring
- inorganic
- solid
- crystalline (orderly internal structure)
- definite chemical composition
3Mafic 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.
4Rocks, 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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6Igneous 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.
7Igneous 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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10Sedimentary 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
12Detrital Sedimentary Rocks
13Chemical Sedimentary Rocks
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15Metamorphism
- 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
16Metamorphism
- Type
- Contact (thermal)
- Hydrothermal
- Regional
- Impact
- Grade (from Low to High)
17Contact Metamorphism
18Hydrothermal 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
19Mid-Atlantic Ridge
20Regional Metamorphism
- Produces the greatest quantity of metamorphic
rock - Associated with mountain building ("orogenesis")
in convergent margin plate tectonic settings
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22Oceanic-Continental Plate Convergence
23Subduction 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
24Continent-Continent Plate Collisions
- Compressional stresses deform the edges of the
plate - Formation of the Earths major mountain belts
including the Alps, Himalayas, and Appalachians
25LOW GRADE
HIGH GRADE
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27Earth 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.
28Metals
- 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)
29Abundant Metals
Abundance is here the estimated percent of the
Earth's crust, by weight.
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32Types 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"
33Contact Metamorphic
At the Cornwall mine in Pennsylvania,
iron-rich fluids from an intrusive Triassic
diabase replaced part of a limestone bed with
magnetite.
34Impact 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
35Regional Compression
36Hydrothermal
Porphyry Copper Deposits are among the richest
ores of hydrothermal origins. The metal is found
in tiny fractures.
37Diagenic
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.
38Placer
- sedimentary layer in which metal ore minerals are
concentrated and from which they can be separated
by density - gold, ilmenite, rutile, hematite
39Residuum ("Brown Ores")
- laterite - old tropical soils with hematite,
goethite, siderite - bauxite - ore of aluminum
40Extracting 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
41Surface 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
42Subsurface 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
43Bingham Canyon mine near Salt Lake City, Utah is
the largest man-made excavation on earth (an
open pit surface mine).
44Abandoned Copper Mine Shaft at Ducktown, North
Carolina (a shaft mine)
45Abandoned Diamond Mine Shaft in Kimberly, South
Africa
46Underground 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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