Test # 3 Study Guide
Chapter 19 - Mineral Resources
Elements are concentrated by various geological processes including:
1) Hydrothermal
2) Magmatic
3) Sedimentary - streams
4) Sedimentary - chemical precipitation
5) Metamorphism - Contact + Regional
6) Weathering
1) Hydrothermal Processes - convection cell
- copper and zinc sulfides, gold, silver
- Black Smokers
- copper sulfides - Bingham Canyon
2) Magmatic Processes (Diamonds)
(Bushveld Intrusion - Chromite)
3) Sedimentary Processes – streams - Placer Deposits
4) Sedimentary Processes - chemical precipitation
5) Metamorphic Processes - Contact
- Regional
6) Weathering Processes
Are these processes related to Plate Tectonics?
How do we classify mineralized prospects ?
Ore Deposits - prospects that can be mined economically
Factors that control if a prospect is economic include:
1) Concentration of the element
2) Ease of separating element (Energy required)
3) Cost of processing ore
4) Value of metal / element
How are materials extracted from the Earth ?
Types of Mining Operations
- Open Pit
- Underground
Processing Facilities - mill complex – ball mills, roasters, smelters
How important is mining to the US Economy ?
$ 5,950 Billion = $22,073 per person / year (Includes both Metallic and nonMetallic Minerals)
How much does the US Economy rely on foreign mineral supplies ?
Platinum Group Elements - 94%
Industrial Diamonds
- 92%
Chromium
- 74%
Lead
- 8%
If USA foreign policies do not appear to make any sense look at the minerals
produced by the country of interest.
Strategic Minerals - minerals / metals crucial to USA national
defense during an international crisis
Strategic and Critical Stockpiling Act (1939)
- 3 year reserve of 35 Strategic Metals and Minerals
- Chromium - stainless steel
- Cobalt
- hardens steel
- Manganese - steel making process (purifying)
- Nickel
- alloy steel, copper-nickel alloys,
- Platinum
- catalytic surface
- Tungsten - making machine tools
- Molybdenum- high pressure lubricant
- Uranium
- nuclear energy
Plate Tectonics – Chapter 12
Q: Have we always thought that the continents moved ?
A: NO - Until ~1915 it was thought that the continents were fixed in place and
did not move
Q: What changed our ideas?
A: Wegener’s proposed the theory of Continental Drift.
A: It proposed that all continents move and that at one time they had all been
fused together in a supercontinent called Pangaea.
Q: What evidence did Wegener use to support Continental Drift ?
A: - Shape of the Continents
- Distribution of:
- Mountain Belts / Rock Types – Lavas/Coal/Tillite in
both S. America and S. Africa
- Dinosaurs - Mesosaurs (similar) / Mammals
(different) - Glossopteris flora (similar)
- Mammals
- Glaciation
Q: How did Wegner propose that continents moved ?
A: he suggested that the continents plowed through the ocean floor or the
movement of the continents was caused by the tidal effects induced by the moon
Q: What were the problems with his theory
A: 1) No evidence that continents plowing through the ocean floor
2) The size of the tidal forces needed to move the continents would cause the
Earth to stop spinning in a few years.
Continental Drift - New Evidence
- Paleomagnetism
- Polar Wandering
-
magnetism recorded in cooling lava
Geomagnetic Reversals
Seafloor Spreading – proposed after Athenosphere discovered
Plate Tectonic Theory
- is a unifying theory that explains most of the geological features and events on
Earth.
- is as important to Geology as the Theory of Evolution is to Biology
Plate Tectonics - Types of Boundaries
There are three types of plate boundaries
1) Divergent / Spreading
2)Convergent / Subduction
3) Transform Fault
1) Divergent / Spreading
- spreading makes crust thin
- thinner crust = less pressure
- less pressure = melting mantle
- warm ocean crust ride higher
- cool ocean crust rides deeper
2)Convergent / Subduction (three types)
A) Oceanic-Continental
B) Oceanic-Oceanic
C) Continental-Continental
3) Transform Fault
Plate Tectonics – Four recent ways of Testing the Theory
1) Earthquake Locations
2) Ocean floor sedimentary and volcanic rocks (oldest <200 my)
3) Hot Spots
4) Global Positioning Satellite (GPS)
- direct measurement of plate movement to corroborate
what we had already estimated from the deep ocean drilling program
(age of sediments and distribution of fossils)
- Spreading centers adding 2 to 20 cm / year
-
Typical Spreading center rate is 5 cm / year (2 inches)
Q: What is causing the plates to move?
A: Escape of heat generated by the decay of the radioactive elements
Uranium, Thorium, and Potassium
Plate Tectonics - in the Central USA (Reelfoot Rift)
- in our immediate area (Midcontinent Rift)
Mass Movement - Mass Wasting – Chapter 13
Q: What is Mass Wasting?
A: Mass Wasting is the process of down-slope movement due to gravity
Mass Wasting - Controlling Factors
- steepness of slope
angle of repose - steepest slope that can be
maintained by a material
Dry Sand
- 35°
Wet Sand
- 9° (as on a beach)
broken rock - 45°
Controlling Factors
Relief - greater relief = greater speed +momentum
Water - acts as a lubricant to reduce cohesion
Extent of Weathering - weathering produces clays that
can facilitate mass movement when wet
Vegetation - Extensive root system helps stabilize
soil, etc.
Geology - foliated rocks, faults, easily weathered rocks
all can enhance mass movement
Slow Processes
- Soil Creep - slow, plastic flow of soils or unconsolidated
sediment slope (rate of millimeters to
centimeters per year).
- Frost Heaving
- Solifluction - flow of water-saturated debris over
impermeable material
Medium Velocity Processes - a few km/hour along
well-defined slip surfaces
Debris Flows (mud slides) occur in arid regions that
are exposed to intense rainfall
Sheetwash - flow of layer of water down hill during a rain storm
High Velocity Processes - up to 100 km/hr
Rockfall - vertical fall; loose rocks break from slope
Rockslide - rapid sliding of bedrock along an inclined surface of weakness
Rock avalanche - rapid movement of a turbulent mass of broken-up bedrock
flows on a cushion of air
Talus Slope - slope established at base of a cliff or ridge by
accumulated debris
- poorly sorted, non-stratified, angular material
Streams – Chapter 14
Hydrologic Cycle
Stream gradient = rise / run
Graded Streams
- amount eroded = amount deposited
- all streams try to become graded
(concave upward longitudinal profile)
Aggradation and Degradation
Evolution of Landscape - Geomorphology
Cycle of Erosion
- sequence of events in the development of landforms
- few areas go through the complete cycle
- there are 4 stages of stream landscapes
1) Youth
- steep gradients
- narrow valleys
- few tributaries
- waterfalls and rapids
- erosion > deposition
2) Maturity
- erosion = deposition (graded)
- no waterfalls and rapids
- wider valleys
- many well-developed tributaries
- meanders
- maximum topographic relief
3) Old Age - valleys have little relief (Peneplain)
- there are no interstream divides (there are Monadnochs)
4) Rejuvenation - uplift of land starts process all over again
- V-shaped valleys
- if meanders already present they become incised
(old-age features but with younger look)
Erosion Factors in Streams – Velocity
- Bed Load
- Suspended Load
- Dissolved Load
1) dissolved load - soil components + minerals in bedrock
dissolved by groundwater
- affected by climate and geological setting
but not by velocity of a stream
- average dissolved load of rivers is 120 ppm
2) suspended load - most important sediment transport method
- usually consists of clay, silt and fine sand
- particle size is a function of stream and settling
velocity.
- Stream velocity is related to turbulence
- Settling velocity is the speed particles fall
through water
3) bed load - coarse particles that move along bottom of stream
because they are too large
- particles can move by rolling, sliding or saltation
- saltation is the bouncing or skipping of material of
the bottom
Capacity and Competence of a Stream
Capacity - total amount of sediment a stream can carry
under a given set of conditions
Competence - largest diameter of particle a stream can move
- competence is ∝ to the velocity squared
- greatest amount of erosion by streams during
floods is caused by an increase in competence
-
Capacity of a Stream at various velocities
Stream Profile
Adjustments with increased flow
Adjustments with Shape of Stream
Effects of Transport on Sediment Particles
- rounding - by abrasion
- sorting
- varies with competence
Meandering Streams
- streams meander at a low gradient and slow flow rate
- meanders have both zones of erosion and deposition
- length of meanders is proportional to width of river, stream
- scrolls are alternating light and dark banding caused by the deposition
of sediments at point bars
- Cutoffs/Necks and the Formation of Oxbow Lakes
- Oxbow Lakes filled with sediment and vegetation are called meander
scars
- shortens channel length + increase stream gradient
Deposition by Streams (fluvial deposits)
- deposition occurs when streams lose velocity
Velocity decrease because:
1) lower gradient
2) flow into still or slow moving water (lake-lacustrine deposits)
3) seasonal precipitation changes (less water, velocity slow)
4) changes in channel shape (widening)
Erosion and Deposition Features
Natural Levees - coarse material deposited near stream channel during a flood
Flood Plain - result of lateral and vertical erosion/deposition
Braided Streams - result of deposition and formation of bars
- main channel split into many smaller ones
Deltas - form where streams enter standing water
Distributary System - “birds foot” pattern of streams over surface of delta
Alluvial Fans - terrestrial counterpart of a delta
- form in arid climates
Base Level - lowest level of downcutting by a stream
- ultimate base level = sea level
-
temporary base level = lake or reservoir
Stream Terraces
- stream valley fills with sediment due to changes in climate, base level, stream
energy
- increase in flow (uplift) causes stream to cut down through old alluvium and
creates new flood plains
Q: How do we describe streams?
A: Dendritic, Radial, Rectangular, Trellis
Flooding
Upstream type - heavy precipitation causes small floods
Downstream type - large floods because of flat topography
- Recurrence interval (years)
Flooding - Factors contributing to floods
- pavement - prevents water from going into the ground
- straightened channels - increases stream gradient and decreases
lag time
Groundwater - Chapter 15
Q: What is Groundwater?
A: Groundwater is water that is stored in:
- pores in soil
- cracks in rocks
- cavities in limestone terrains
- fractures in faults
- vesicules in volcanic rocks (voids formed
by gas escaping from a magma)
Q: How much Groundwater do we have ?
A: Groundwater = 96% of all available fresh water
Q: Why should we study Groundwater?
A: Understanding groundwater is important because it
supplies - 50% of US drinking water
- 40% of irrigation water used in the US
- 25% of water used by industry in the US
- overall it supplies 40% of all water used in the US
Over use of groundwater resources can:
1) result in water shortages
2) stream-flow depletion
3) land subsidence
4) contamination by salt water
5) increased pumping costs
6) groundwater pollution
Q: Where does Groundwater come from?
A: Groundwater comes from meteoric water - (atmospheric precipitation)
connate water - water trapped during the
deposition of sediments (brines)
juvenile water - water released by magma
(e.g. Mt. St. Helens)
Q: How fast can Groundwater move?
A: Groundwater moves centimeters/day (much slower than a stream or river)
The speed of groundwater movement is a function of the porosity, permeability
and slope of the soils/rocks through which the water is moving.
porosity (%) = volume of pore space
total volume of soil (or rock)
In general porosity
<5% - low porosity
5 - 15%
- medium porosity
>15%
- high porosity
Q: What factors affect Porosity ?
A: Roundness, Sorting, Cementing
Q: Does a large Porosity ensure that there will be abundant water in a well?
A: No, if the soil/rock is not permeable enough it won’t let the water flow into
the well
Permeability - the ability for a rock or soil to
transmit water (gpd/sq.ft.)
- is a function of how well pores are
connected
- poorly connected = low permeability
-
well connected = high permeability
Q: What role does slope (hydraulic gradient) play in the movement of water ?
A: …………
Q: Can water flow to the surface of the Earth on its own ?
A: Yes! In a Spring.
Q: What causes a Spring to form ?
A: To produce a spring in an unconfined aquifer you need:
1) A porous and permeable soil or rock unit through which the water can flow
2) A perched water table on top of an aquitard (aquiclude)
3) Precipitation to feed the aquifer
4) Substantial variations in topography so that the water table intersects the
surface of the land (this alone can produce a spring sometimes)
Q: Is this the only way water flows to surface on its own ?
A: No! Water also flows to surface in Artesian springs ?
Q: Why does Water flow to surface in an Artesian spring ?
A: To produce an Artesian Spring you need four things:
1) A permeable aquifer confined between two aquitards
2) the aquifer must have a dip
3) there must be a recharge zone located at the highest point
4) there must be a fracture or well so water can escape from
the aquifer
Q: Do you encounter artesian springs in your everyday life?
A: Yes – City water supply system
Q: Does water come to surface by any other means?
A: Yes! In Geysers and Hot Springs
Q: Why is Old Faithful, Faithful ?
A: Old Faithful is faithful because it has
1) complex plumbing system with a restricted exit pathway
2) heating by hot, igneous rocks that intruded area
3) Steam pressure buildup as water is heated
4) flash boiling
Warm / Hot Springs
Are caused by:
- hot igneous rocks
- deeply circulating meteoric water that is heated by the thermal gradient in the
earth’s crust (30°-60°C/km)
- water released by regional metamorphism (e.g. chlorite - (Mg,
Fe)12[(Si,Al)8O20](OH)16)
Groundwater - Karst Systems
Glaciers – Chapter 15
Concepts / Topics covered in this Lecture
- How do glaciers form?
- How and how fast does a glacier move?
- What features are formed by glaciers?
- Why do Ice Ages occur?
Q: What is a Glacier ?
A: A glacier is a slow moving mass of ice formed by the recrystallization of snow
Q: How do Glaciers Form ?
A: 1) More snow falls than melts annually in zone of accumulation
- climate cools
- precipitation increases in a cold climate
2) Snow needs to be converted to glacial ice
Q: Where do Glaciers Form ?
A: at high latitudes - continental type (move radially under own weight)
at high altitudes - Alpine/valley type glacier that move by gravity
- Piedmont glaciers - a number of Alpine glaciers flow together and coalesce into
a large apron of ice at the base of the mountains
Q: Do Glaciers Move ?
A: Evidence that Glaciers Move includes
- row of stakes placed on glacier will move with time
- rocks in glacier are different than those in the adjacent
wallrocks
- rocks under a glacier are polished, grooved and
scratched
- shear zones are present in the glacial ice
Q: How does a glacier move ?
A: A glacier moves by internal deformation called plastic flow and by sliding over
the bedrock by basal slip
Q: How fast does a glacier move ?
A: - Typical rates of movement are 0.5 to 2 meters / day
- Glaciers can surge at rates of up to 200 meters / day
Q: What factors influence the speed of a glacier ?
A: - topography (relief)
- temperature (amount of H2O)
- thickness (thicker = faster)
- smoothness of bedrock surface
Q: How do glaciers cause erosion?
A: - Along valley walls - frost action, landslides, avalanches
Along valley floor - plucking and quarrying, abrasion of valley floor, along
valley floor, glacial striations, rock flour (Loess - wind-blown rock flour)
Erosional Features
Alpine – U-shaped valley, Hanging valley, Cirque, Horn, Arrette, Truncated Spur,
Tarn
Continental – Terminal Moraine, Basal Moraine, Drumlin, Outwash Plain, Kettle
Lake, Esker, Roche Moutonnee, Kame, Erratic, Raised Beaches
Deserts and Winds – Chapter 17
Q: What is a desert ?
A: literally means deserted or unoccupied place
Q: - What are the characteristics of a desert environment ?
A:
- low annual precipitation / arid (<25 cm / year)
- highly permeable ground
- deep water table
- lack of vegetation (in most deserts)
Q: - Where do deserts occur on Earth ?
A: - Mid-latitudes
Q: - What controls the formation of deserts ?
A:
1) - high pressure zones
2) - location of mountain ranges
3) - cold water currents
4) - distance from an ocean
5) - cold climates
Q: - What causes weathering in a desert ?
A: The principal agents of weathering in a desert are:
1) rainfall
2) force of the wind
Q: - How much weathering is there and what are the products?
A: There is less weathering in deserts than in most places on Earth because
there is little water and organic acids (from organic matter).
Q: - How does water contribute to erosion in a desert ?
A:
A) rainfall occurs as downpours during the monsoon season
B) Streams are ephemeral
- streams are mostly in an interior drainage basin
- rainfall occurs only during occasional storms
-
streams flow for only a few hours to a few days
-
streams are often subject to flash flooding
C) Ephemeral streams cause:
- most of the erosion in a desert
- erosion by water is mostly mechanical (abrasion)
Q: - What types of desert features are formed by water ?
A: Erosional
- wash / arroyo
- canyons
- angular hills
- desert pavement (pebble/sand covered desert floor)
- plateau, mesa, butte, hoodoos
- pediment
- inselberg
A: Depositional
- Alluvial Fans (Bajada)
- Playas (with or without temporary salt lakes)
- Desert Plain
Q: - How does wind contribute to erosion in a desert ?
A: 1) wind becomes an important erosion agent after desert plain forms
2) Wind Moves particles of rock/mineral
- depends on wind velocity and direction
- hindered by moisture and vegetation
- depends on particle size
- dust (<0.06 mm) carried by suspension 100’s to 1000’s of meters in the
air by dust storms
- sand (~0.15 to 0.30 mm) carried by saltation 1 m or less above the
ground by sand storms
cobbles are moved by creep
- deflation - lowering of desert surface by removal of fine-grained unconsolidated
material by the wind
- desert pavement produced by deflation
Q: - What types of features are formed by desert winds ?
A: - “blowout” basins that measure m - km across
- loess deposits - yellowish-tan-brown angular
- wind-blown deposit
- cm to m thick in central USA
- associated with glacial deposits
- sand dunes – various dune types provide indication of wind direction
Q: How can we identify Ancient dune deposits ?
A: - typically large-scale, concave upward cross-bedding
- quartz has a frosted texture caused by sand-blasting
- quartz dominant sand, ventifacts present
Q: Why would we want to identify Ancient dune deposits ?
A: - provide clues about paleowind direction, paleoclimate
and possibly paleolatitude