Chapter 9 - Economic and engineering geology Flashcards
what are the factors affecting porosity?
degree of sorting
amount of diagenesis
grain shape
packing of the grains
what are the factors affecting permeability?
porosity
temperature
secondary permeability
capillary pressure
how do you calcualte hydraulic gradient?
difference in hydrostatic pressure or hydrostatic head / difference between 2 points
What is the equation for darceys law and what do each letter equate to?
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
What are the types of springs?
lithological spring
fault spring
unconformity spring
seeps
what are the problems of groundwater extraction?
lowers water table
subsidence
saltwater enchroachment (coastal)
what are the 2 threats to groundwater supply?
over pumping (cone of depression)
pollution
what are the sources of groundwater pollution?
nitrates
hydrocarbons from petroleum
toxic fluids from landfill
acid mine drainage
what are some key terms for metallic mineral extraction?
cut off grade
grade
gangue minerals
concentration factor
average crustal abundance
ore deposit
what affects the cut off grade?
value
demand
abundance
size of ore deposit
cost of extraction
what is the concentration factor equation?
concentration factor = concentration of metal in ore (grade) / average crustal abundance
What happens above and below the water table in secondary enrichment of copper?
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
what is it called when hydrothermal fluid creates a secondary deposit?
porphyry copper deposit
what are good qualities for minerals in placer deposits?
hard
chemically unreactive
dense
what are the sites of placer minerals?
meander bends
plunge pools
upstream of projections
downstream of confluences
beaches
Describe key characteristics of gravity surveys:
- 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)
Describe key characteristics of magnetic surveys:
- small variations in magnetic field
- measured in nanoteslas
- minerals rich in iron
Describe the key charactersics of electromagnetic surveys:
- 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
Describe the key characteristics of electrical resistivity surveys:
- 2 electrodes with electrc current
- good conductor = low resistance (metals)
what are the geochemical exploration techniques?
stream sediment sampling
soil sampling
water sampling
vegetation sampling
what are the process of explorng for minerals?
geophysical/chemical surveys
target selection
exploration drilling
estimating reserves
What is involved in target selection?
stats tests
comparisons
GIS
what is involved at exploration drilling?
- drilled at angle (cores)
- downhole logging
- type, size, depth, how to access
What affects profitability?
- grade
- operationsal (type of mine, methods, pollution management)
- economic (setting up, long term projections for price)
