Chapter 9- Economic and engineering geology Flashcards
(134 cards)
1
Q
total porosity of a rock
A
total porosity = pore space volume / bulk volume
2
Q
primary porosity
A
pore spaces at the time the sediments were deposited
3
Q
secondary porosity
A
develops in the rock after deposition, includes cavities or fractures that have formed
4
Q
effective porosity
A
the total porosity minus any cement and contributes to fluid flow through the rock. Clean sands have an effective porosity that is almost equal to the total porosity
5
Q
porosity
A
volume of pore space in a rock/sediment. usually expressed as a percentage of total rock volume. can also be a measure of the rocks ability to store/contain fluids
6
Q
permeability
A
ability of a rock/sediment to transmit fluids such as water, oil, or gas, and can be expressed as a rate of flow of the fluid through the rock or sediment
7
Q
formula to calculate permeability
A
permeability = distance fluid has travelled / time taken
8
Q
factors effecting porosity
A
-degree of sorting
-amount of diagenesis
-grain shape
-packing of the grains
-secondary porosity
9
Q
factors effecting permeability
A
-porosity
-temperature
-secondary permeability
-capillary pressure
10
Q
capillary pressure
A
pressure between two immiscible fluids in narrow pore spaces, resulting from interactions of forces between fluids and solid grains
11
Q
connate water
A
trapped in the pores of a rock as the rock formed. it includes water trapped in the original sediment and water released during diagenesis
12
Q
groundwater
A
water occupying pores and other spaces in rocks and sediments which is derived mostly from rainfall percolating into the underlying rock
13
Q
water table
A
the surface separating unsaturated rock above from unsaturated rock below
14
Q
hydrostatic pressure
A
the pressure at a point in a body of water due to the mass of the overlying column of water
15
Q
hydraulic gradient
A
difference in hydrostatic pressure between two points divided by the distance between them
16
Q
aquifer
A
a body of porous and permeable rock capable of storing and yielding significant amounts of water
17
Q
darcy’s law
A
Q (rate of flow) = - K (coefficient of permeability) x A (cross sectional area in square meters) x (h1-h2/L) (hydraulic gradient)
18
Q
recharge zone
A
the area of an aquifer open to the atmosphere, allowing replenishment of water
19
Q
artesian basin
A
a large, synclinal confined aquifer under hydrostatic pressure
20
Q
artesian wells
A
hold water under hydrostatic pressure, which rises up the well to the piezometric surface on release
21
Q
piezometric surface
A
an imaginary surface to which groundwater rises under hydrostatic pressure to produce springs
22
Q
abstraction
A
the removal of water from any source
23
Q
types of springs
A
-lithological
-at faults
-at conformities
-seeps
24
Q
aquiclude
A
an impermeable rock that does not transmit water
25
aquitard
a rock which has very low permeability and only allows the transmission of water at very low rates
26
cones of depression
occur when there is a lowering of the water table in the vicinity of a well, usually due to abstraction of water
27
problems caused by groundwater abstraction
-lowering of the water table
-subsidence
-saltwater encroachment in coastal areas
28
threats to groundwater supply
-over pumping - not enough water left to provide a reliable public water supply
-pollution entering the groundwater when it is vulnerable as the groundwater usually acts as a natural filter
29
soluble minerals in groundwater
-'hard' groundwater contains Ca2+ and Mg2+ ions. harmless to drink but leaves limescale in kettles/difficult to form a lather with soap
-some groundwater contains F- ions, can reduce tooth decay but in high volumes is linked to dental fluorosis
-in some places, ie parts of south asia, the groundwater has naturally high levels of asenic, making it unsafe for human consumption
30
sources of groundwater pollution
-nitrates, pesticides, and microbes from agricultural runoff and sewage
-hydrocarbons and solvents from petrol stations and factories
-toxic fluids from landfill waste disposal sites
-acid mine drainage water containing toxic metals such as lead and cadmium from abandoned coal and metal mines
31
acid mine drainage
caused when water flows over o through sulfur bearing materials, ie rocks containing iron pyrites. causes acidification of the water
32
ore
rock containing valuable metals that is economic to mine
33
resource
useful and valuable natural mineral
34
mineral resources
can be metallic and non metallic or industrial minerals
35
reserves
amount of a resource that can be extracted at a profit using existing technology
36
ore deposit
an accumulation of metal that may be economic to mine
37
average crustal abundance
describes the amount of metal in 'average' continental crust
38
concentration factor
the amount by which a metal is concentrated to make an ore deposit
39
ore mineral
a mineral containing valuable metals
40
gangue mineral
a low-value waste mineral
41
grade
refers to concentration of valuable minerals within an ore
42
cut- off grade
the grade below which it is uneconomic to mine
43
what determines cut off grade
-value of the metal
-demand
-abundance of the metal
-size of the ore deposit
-cost of mining and extraction
44
ore mineral of copper
chalcopyrite- CuFeS2
45
oe mineral of gold
gold- Au
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oe mineral of iron
magnetite- Fe3O4
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ore mineral of lead
galena- PbS
48
ore mineral of tin
cassiterite SnO2
49
ore mineral of zinc
sphalerite ZnS
50
formula to calculate concentration factor
CF= concentration(grade) of mineral in ore / average crustal abundance
51
secondary enrichment
occurs when metals are leached from within surface rocks and precipitated just below the water table
52
chemical weathering
in situ breakdown of rocks at the earth's surface due to chemical reactions
53
leaching
where ions are dissolved from rocks and carried downward in solution
54
gossan
an insoluble cap of iron oxides at the surface of a mineral vein
55
oxidising
describes oxygen rich conditions, allowing elements to combine more readily with oxygen to form oxides
56
reducing
describes oxygen poor conditions/ anoix
57
enriched deposit
a zone of high grade ore just below the water table, formed by secondary enrichment
58
porphyry
a large igneous intrusion with porphyritic texture
59
placer deposit
surface deposits formed by sedimentary processes (weathering/erosion/transport/deposition)
60
dredging
when material is scraped or sucked from a river or sea bed
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hydraulic mining
use of high pressure water jets to dislodge material
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sights of deposition of placer minerals
meander bends
plunge pools
upstream of projections
downstream of confluences
on beaches
63
advantages of placer mining
-easily accessible and cheap to mine
64
disadvantages of placer mining
immediate environmental impacts- scars on landsurface, dust and noise, stirring up of silt
tend to be small and therefore quickly exhausted
65
geophysical exploration techniques- used to find metals
-gravity surveys
-magnetic surveys
-electromagnetic surveys
-electrical resistivity surveys
66
geochemical exploration techniques
-stream sediment sampling
-soil sampling
-water sampling
-vegetation sampling
67
geophysical anomaly
a departure from the normal value- may be positive or negative
68
geochemical anomaly
a concentration of a metal above its normal background value
69
dispersion
occurs when small amounts of metals are spread out around the ore deposit by surface processes of weathering, erosion, and transport
70
catastrophic dilution
occurs where tributaries meet and water and sediment from other sources are added
71
geographical information survey
GIS- a computer application used to store, view, and analyse spatial information, especially maps
72
stages of exploring for metals
-initial surveys- target selection- mapping and further surveys- trench digging- exploration drilling- estimating reserves
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geological considerations/ what determines the computer modelling used
-the geological setting
-if there are areas of high grade ore (nugget effect)
-styles and zonation of the mineralisation
-if the mineralisation has sharp or gradational boundaries
-how easy the rock is to work
-presence of toxic elements ie arsenic
74
operational considerations/ what controls if the ore can be extracted at a profit
- type of mine and its stability (open pit or underground)
-methods and rates of extraction and processing
-pollution management and acid mine drainage
-dilution by waste rock mixed with ore
-water control, drainage, and pumping
75
economic considerations
-set up costs, including assembling the plant
-level at which the cut off grade is set
-long term projections for the metal prices for the ore
-closure and reclamation plans
76
factors affecting the accuracy of the reserves estimate
-detail of the survey
-variation in grade of the mineral and size of the ore body
-unexpected geological conditions ie faulting
-unrecorded earlier workings
-variations in economic climate and demand
-improvements in extracting technology
77
sustainability
using a resource so that it is not depleted or harmful to the environment, supporting a long term balance in ecological and other conditions
78
non-renewable resources
do not renew themselves at sufficient rate for sustainable economic extraction in a human lifetime
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open cast mining
mining from surface quarries
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shafts
vertical openings to an underground mine
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stope
void left when the ore has been extracted from an underground mine
82
life cycle of a mine
-design and planning
-construction
-production
-processing
-rehabilitation and reclamation
83
flotation tailings
the waste rock fragments that do not attach to bubbles in the froth flotation process
84
in situ leaching at depth
-bore holes are drilled into the ore deposit and opened up by fracturing
-leaching solution is pumped down to the ore
-the solution carrying the dissolved ore is pumped back to the surface via a second borehole
-evaporites are extracted using water
-uranium uses acids of sodium hydogen carbonate
-copper uses acids
85
heap leaching at the surface
-ore is crushed and heaped onto a plastic or clay liner
-leaching solution is applied by spray or drip
-dissolved material accumulates in a pond and is taken for processing
-cheap but only recovers 60-70% of the ore, and can take up to two years
86
froth flotation
-separates hydrophobic from hydrophilic material
-yields significant amount of metal from low grade ores
-ore is crushed and mixed with water to form a slurry, target mineral is made hydrophobic by adding relevant chemicals
-slurry is fed into a flotation cell which is aerated to produce bubbles- hydrophobic material latches onto the bubbles and is brought to the surface
-flotation tailings are removed and the process is repeated to maximise recovery
87
disposal of tailings
-often containing toxic elements and harmful chemicals
-radioactive uranium tailings are particularly harzardous
-previous methods involve storage underground however leakage can cause severe environmental problems
88
smelting
-extraction of elemental metal from on ore in a blast furnace
-ore minerals combine with oxygen, carbon or similar
-produce a lot of greenhouse gasses, ie co2 and so2
-have been know to create dead zones
89
managing minewater
- source control
-migration control
-active treatment
-passive treatment
90
leachate
liquid that drains or leaches from landfill sites. created by rainwater mixing with microbes in the landfill
91
pollution plumes
zones of contamination, usually into an aquifer or water sources. can be from various sources, including leachate from landfill sites
92
transuranic elements
hate atomic numbers greater than 92 (that of uranium). they are unstable and decay radioactively into daughter elements
93
carbon sequestration
a process where CO2 is removed from the atmosphere and held in an alternative form, either solid or liquid
94
nuclear waste disposal
-low level radioactive waste can be disposed of in secure landfill sites
-criteria for disposing of high level radioactive waste:
.isolation for at lest 250,000 years
.secure from accidental or deliberate entry
.safe from natural disasters
.no chance of leakage
suggestions include
-launching it into space
-burial in sea floor sediments near subduction zones
-ice sheets
-underground geological repository
an underground geological repository would need to be
-tectonically stable area
-dry impermeable rocks with a low water table
-fee from effects of potential hazards
-dry competent rocks ie granite or volcanic rocks
-evaporites were researched but the risk of saline water corroding the container was too great
95
overbreak
too much rock is extracted
96
underbreak
too little rock is extracted
97
geological factors affecting construction of tunnels
-'hard' rocks- over/underbreak, expensive, confining pressure can cause dangerous bursts
-'soft' rocks, cheaper but require stabilising
-weak rocks are prone to leakage and collapse
-lateral variation/changes in rock type
-attitude of the strata- slippage along bedding planes
-geological structures
-groundwater
-spoil
98
methods to prevent collapse and flooding of tunnels
-lining with concrete or steal ribs
-rock bolts
-grouting surrounding rocks
-rock drains
99
reservoirs
bodies of water behind a dam wall
100
dams
structures that hold back water
101
geological factors affecting construction of dams/reservoirs
-general conditions, ie presence of earthquakes/volcanoes, rainfall, potential for mass movement
-underlying rock types
-attitude of the strata
-geological structures
102
types of dams
-masonary/concrete dams
.arch dam
.gravity dam
.arch-gravity dam
-embankment/earth dams
103
methods to prevent leakage from reservoirs
-grouting
-clay/plastic lining or geomembrane
-cut off curtain
104
environmental and social consequences of dam/reservoir construction
-flooding of land for the reservoir may destroy agricultural land, villages, or valuable archaeological sites. Where forests are flooded, the decaying vegetation releases large quantities of CO2
-damage to aquatic ecosystems may be caused downstream- ie changes in water depth, temperature, oxygen content
-water released from dams contains very little sediment, leading to clear water erosion
-above average snow melt or rainfall may not leave enough time to draw down the reservoir to prevent flooding
105
inert
substances are chemically inactive
106
bioavaliability
proportion of total metals available for for incorporation into biota. varies with pH
107
bioaccumulation
occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost by catabolism and excretion. The substance becomes concentrated in the organism
108
ion exchange
exchange of ions between two electrolytes or between an electrolyte solution and a complex. describes purification/decontamination of ion-containing solutions
109
adsorption
process by which particles such as heavy metal ions become semi-permanently attached to the surface of a clay mineral
110
isomorphous substitution
replacement of one atom by another of a similar size in a crystal lattice during crystal growth without changing the crystal structure. It takes place only between ions with less than 15% radii difference
111
sources of pollution
-inert waste
-agriculture- organic material ans hazardous chemicals
-brownfield sites
112
methods of remediation of contaminated land and groundwater
-phytoremediation
-stabilisation and solidification
groundwater treatments - ion exchange/caustic soda
113
fossil fuel
made from remains of once living organisms. coal, oil, and natural gas
114
petroleum
includes natural gas, oil, and asphalt
115
source rock
organic-rich mudstone or shale which contained abundant plankton that formed in a low energy, anoxic, marine, condition
116
reservoir rock
highly porous and permeable rock, capable of storing and yielding significant amounts of petroleum
117
caprock
the impermeable rock above a reservoir rock preventing further upward migration of petroleum
118
hydrocarbon
includes any compound made just of hydrogen and carbon. it is often used as a general term to refer to oil and natural gas. The simplest is methane CH4
119
sapropel
unconsolidated, dark coloured, organic rich deposit which becomes the source rock
120
kerogen
solid, bituminous material in source rocks which forms oil when distilled
121
maturation process
converts plankton into petroleum by increasing temperature and pressure during burial
122
oil window
temperature and pressure conditions under which oil can form
(50-100 degees, 2-3km)
123
gas window
temperature and pressure conditions under which gas can form
(100-200 degrees, 3-7km)
124
migration
the movement of petroleum from a source rock to a reservoir rock
125
trap
geological situations that concentrate petroleum in one place
126
types of oil and gas traps
-anticline trap
-fault trap
-salt dome trap
-unconformity trap
-lithological trap
127
traps, reservoir rocks, and cap rocks in the Kimmeridge Clay (north sea)
fault, lithological, and anticline
sandstones and chalks
clays and mudstones
128
geophysical exploration techniques for oil and gas
seismic reflection surveys
gravity surveys
129
methods of exploration drilling
mud logging
hole sampling
down hole logging
stratigraphic correlation
130
primary recovery
-oil gushes to the surface under natural pressure
-submersible pumps/beam pumps ie nodding donkeys
-20-30% of oil is recovered
131
secondary recovery
-injection of water or gas
-increasing the temperature
-use of chemicals
-use of bacteria
-40-60% recovered
-20-30% remains unrecoverable
132
advanced drilling techniques
-multiple well/multi lateral drilling
-extended reach drilling
-horizontal drilling
-complex path drilling
133
unconventional petroleum sources
-oil shale
-tar sands
-extra heavy oil, mixed with water or other types of crude oils
-frozen gas hydrates
134
hydraulic fracturing
-drills and lines a borehole. High pressure water is pumped into the shale to force open cracks, held open with sand grains
