Chapter 9 - Economic and engineering geology

Question 1

what are the factors affecting porosity?

Answer 1

degree of sorting
amount of diagenesis
grain shape
packing of the grains

Question 2

what are the factors affecting permeability?

Answer 2

porosity
temperature
secondary permeability
capillary pressure

Question 3

how do you calcualte hydraulic gradient?

Answer 3

difference in hydrostatic pressure or hydrostatic head / difference between 2 points

Question 4

What is the equation for darceys law and what do each letter equate to?

Answer 4

Q = -KA((h2-h1)/L)

Q = rate of flow
K = coefficint of permeability
A = cross sectional area in square metres
((H2-h1)/L) hydraulic gradient

Question 5

What are the types of springs?

Answer 5

lithological spring
fault spring
unconformity spring
seeps

Question 6

what are the problems of groundwater extraction?

Answer 6

lowers water table
subsidence
saltwater enchroachment (coastal)

Question 7

what are the 2 threats to groundwater supply?

Answer 7

over pumping (cone of depression)
pollution

Question 8

what are the sources of groundwater pollution?

Answer 8

nitrates
hydrocarbons from petroleum
toxic fluids from landfill
acid mine drainage

Question 9

what are some key terms for metallic mineral extraction?

Answer 9

cut off grade
grade
gangue minerals
concentration factor
average crustal abundance
ore deposit

Question 10

what affects the cut off grade?

Answer 10

value
demand
abundance
size of ore deposit
cost of extraction

Question 11

what is the concentration factor equation?

Answer 11

concentration factor = concentration of metal in ore (grade) / average crustal abundance

Question 12

What happens above and below the water table in secondary enrichment of copper?

Answer 12

above - rainwater percolates down, soluble copper silfates dissolve. Leached zone left behind with a cap called gossan (insoluble iron oxides)

below - copper sulfates become insoluble copper sullfide in reducing conditions

Question 13

what is it called when hydrothermal fluid creates a secondary deposit?

Answer 13

porphyry copper deposit

Question 14

what are good qualities for minerals in placer deposits?

Answer 14

hard
chemically unreactive
dense

Question 15

what are the sites of placer minerals?

Answer 15

meander bends
plunge pools
upstream of projections
downstream of confluences
beaches

Question 16

Describe key characteristics of gravity surveys:

Answer 16

• gravitometer
• measured in milligals
• data is corrected for lattitude/altitude/free air/topography (any change is due to rocks)
• plotted on colour maps with isolines
• look for high density

Positive: high dense magic intrusion (metallic ore minerals)

Ngeative: low dense silicic intrusion (hydrothermal fluid veins)

Question 17

Describe key characteristics of magnetic surveys:

Answer 17

• small variations in magnetic field
• measured in nanoteslas
• minerals rich in iron

Question 18

Describe the key charactersics of electromagnetic surveys:

Answer 18

• EM waves from transmitter inducing currents in conductive minerals e.g metals
• uses waves from VLF signals
• given as percentage of secondary field relative to primary field
• metal sulfides e.g chalcopyrite

Question 19

Describe the key characteristics of electrical resistivity surveys:

Answer 19

• 2 electrodes with electrc current
• good conductor = low resistance (metals)

Question 20

what are the geochemical exploration techniques?

Answer 20

stream sediment sampling
soil sampling
water sampling
vegetation sampling

Question 21

what are the process of explorng for minerals?

Answer 21

geophysical/chemical surveys
target selection
exploration drilling
estimating reserves

Question 22

What is involved in target selection?

Answer 22

stats tests
comparisons
GIS

Question 23

what is involved at exploration drilling?

Answer 23

• drilled at angle (cores)
• downhole logging
• type, size, depth, how to access

Question 24

What affects profitability?

Answer 24

• grade
• operationsal (type of mine, methods, pollution management)
• economic (setting up, long term projections for price)

Question 25

why might profitability change?

Answer 25

• variation in grade
• unexpected conditions (faults)
• unrecorded mines
• variations in economic climate
• improved technology

Question 26

Describe the life cycle of a mine:

Answer 26

1- design and planning
2- construction
3 - production
4 - processing
5 - rehab and reclamation

Question 27

Types of mining:

Answer 27

open cast mining
stoping
punch longwall mining

in situ leaching
froth flotation process (target mineral hydrophobic)
heap leaching
smelting

Question 28

What are the ways of managing minewater?

Answer 28

source control (water removed)
migration control (neutralise)
actiev treatment
passive treatment

Question 29

storing waste underground edit

Answer 29

page 202

Question 30

what geological factors affect the construction of tunnels?

Answer 30

igneous/metamorphic
soft rocks
weak rocks
lateral variation in rock types
attitude of strata

Question 31

what geological structures affect the contruction of tunnels?

Answer 31

faults
joints
bedding planes
folded rocks

Question 32

what is the material dumped away after extraction called?

Answer 32

spoil

Question 33

what methods are used to prevent tunnel collapse?

Answer 33

shotcrete
rock nolts
grouting (h20)
rock drains (h20)

Question 34

what affects where dams are built?

Answer 34

faults
rock type
attitude of strata
geological structures

horizontal beds - stable
dip downstream - unstable
dip upstream - stable

Question 35

what are the types of dams?

Answer 35

masonry/concrete
- arch : curved upstream
- gravity
- arch-gravity

embankment/earth dams

Question 36

what is done to prevent leakage from dams?

Answer 36

grouting - cement pumped into pores
plastic lining
cut-off curtain

Question 37

What hazards are associated with dams?

Answer 37

Resevoir-induced Seismicity (RIS)
water infiltrates pores under hydrostatic pressure and lubricates fractures

Question 38

contaminated land and groundwater

Answer 38

pages 210-211