Exploration of minerals Flashcards
Concentration factor equation
Grade (%) ÷ average crystal abundance (%)
What is the main ore mineral for copper??
Chalcopyrite CuFes2
what is secondary enrichment??
when metal ore is leeched from within surface rocks and precipitate just below WT
Formation of chalcopyrite
hydrothermal fluids dissolve copper from I rocks
precipitate in surrounding contact met sed rocks
often found in hydrothermal veins
Why don’t we exploit copper from chalcopyrite
Conc factor not high enough
not at cut off grade
part of resource not reserve
inaccessible
Flow diagram for secondary enrichment
(of chalcopyrite)
Chalcopyrite
In forms of sulphides - insoluble in H20
Chalcopyrite exposed and chem weathering /oxidation
produces copper sulphate
this is soluble in H20
percolates down in ground
reaches WT = saturated and anaerobic
reduced + dep as Cu just below WT
now much more conc and econ viable to mine
What is gossan?
an insoluble cap of iron oxide at the surface of a mineral vein
why are gossans useful
marker for Cu below surface left over from secondary enrichment of chalcopyrite
porphyry def
a large igneous intrusion with a porphyritic texture (2 stage cooling)
formation of porphyry cooper dep
flow diagram
form as a result of hydrothermal processes associated with granite intrusions at convergent plate margins
C plate boundary
melting
granite intrusion (S and wet) high H20
M chamber cools and common S minerals form e.g. quartz and feldspar
Leftover= H2O and incompetent metals e.g. Au Cu U Mo called at top of M chamber
some crystals take up more space as solid rather than liquid
less space pressure builds
surrounding C rock fractures
hydrothermal fluid moves away from porphyry and cools
metals are dep /come out of solution along fractures as come out of solution at diff temps
form mineral veins
What is a Placer deposit
surface deposits formed by sed processes of weathering and erosion, transport and dep
why are Placer dep important
Dense physically and chem resistant mineral e.g. cassiterite , gold and diamond can be converted by these processes until small but high grade ore dep
How do Placer deps form?
weathering
ore is broken up by mech/
left as insoluble metals by chem
ore and gangue sep into individual grains
weather metals transported by H20 in river + sea (sorted by grain size hardness and density)
when velocity slows preferentially dep as ore mix with unconsolidated sand and gravel
become conc as resistant to erosion and being dissolved
all mins have sim properties: hard + little cleavage, unreactive so don’t dissolve,dense- dep first
5 places placer deposits form
Meander bends
plunge pools
upstream projections
downstream confluences
on beaches
How do placers form on meandering bends?
current swings around outside bend
velocity higher on outside
lower inside
results in dep on inside (placer dep) and erosion on outside
how do placer deps form in plunge pools
river flows erodes less resistant rock creating waterfall
turbulent water and boulder at bottom of waterfall scour out deep hollow
plunge pool
dense placer min trapped in sed in plunge pool
how do placer deps form at upstream projections
projections e.g. Dykes in river bed will trap dense placer mineral
on upstream side
may be where hard rock projects out or just small scale like ripples
how do placers form downstream of confluences
fast flowing tributary joins slower flow river
current drops
dense placer min dep into mid channel sandbar
how do placers form on beaches (incomplete)
4 geophysical techniques for exploration of minerals
Gravity surveys
magnetic surveys
electromagnetic surveys
electrical resistivity survey
Gravity surveys
gravimeter - measures variations in grav field strengths
shows varied results from rocks and mins
plotted with lines showing equal strengths
+= high density metal ore/ M or UM intrusion
-= low density S intrusion e.g. hydrothermal vein or oil + gas or aquifer
magnetic survey
magnetometer measures variation in mag field strength
+= rich in Mg and Fe
due to M or UM intrusion (may contain cumulate ore dep)
or presence of haematite, magnetite or pyrite
electromagnetic survey
measures ground conductivity using electromagnetic inductor
give value as % of secondary relative field: primary field
electricity produced by transmitted induced current in conductive minerals e.g. metal ore
good for metal sulphide minerals e.g. chalcopyrite
use very low frequency
electrical resistivity survey
2 electrodes placed in ground
pass e current between
if underlying rock good conductor = low res
metals = good conductors so lower res
used for gold exploration
4 geochemical techniques for exploration of minerals
sediment stream sampling
soil sampling
water sampling
vegetation sampling
stream sediment sampling
REWRITE USINF TEXTBOOK
1 to 2 kg collected from beds and analysed for mins of interest
interpretation based on: downstream of source will have anomalous metal values
upstream of source = normal
anomaly downstream due to dep of sed by tributary
anomaly upstream of every cnfluence
soil sampling
COME BACK TO SAMPLING LATER WITH TEXT BOOK
what further exploration occurs post geochem and physical surveys?
promising areas are mapped, may collect min and rock samples
have location and potential grade
GIS used to view and analyse quantitive spatial relationship (creating map from data from surveys) to target selection
then maybe borehole to narrow down ares and test may test in lower value ores
purpose of exploration drilling
provides most accurate info - expensive
diff drills used e.g. diamond for core samples
down hole logging- make borehole large enough for device more geophys surveys
aims to detect: useful/not ore, how much ore present,
grade,
how much gangue is present,
depth and extent of ore body and how it can be used
reserve defenition
metal that can be extracted with todays technology and is economically viable
why is estimating reserves important and what must we know to estimate
help eval deposit
is the reserve probable
makes allowances for waste rock that dilute ore or unavoidable losses
only way to find out if min is profitable to mine it as if not no longer a reserve
kriging method
used in mining to determine size and location of valuable resource
based in comp programs using stats and projections
feed data into program (what and where) use know data from prev sites
produce 3D block image of valuable material and grade
not necessarily correct but improves with each use-machine learning
uses geostats
how are block models of ore body made and why are they useful
made by computer program e.g. kriging
instead of drilling anywhere only drill into blocks with highest grade so cheaper reduces losses and expensive as dont have to mine everywhere
other considerations when determining viability of resource extraction
geological
operational
economic
geological considerations for viability
geological setting
whether areas of V high grade
style and zonation of mineralisation e.g sharp or gradual boundaries
how easy rock is to work into
presence of toxic elements
operational consideration for viability of resource
type of mine and stability e.g. open pit or underground
method, rate of extraction and processing
pollution management and acid mine drainage
dilution of waste rock mixed with ore
water content, drainage and pumping
economic consideration for viability of resource
set up cost- plant assembly
level of cut off grade
long term projections for metal price of ore
closure and reclamation plans as laid out in planning consent
factors effecting accuracy of est of reserve
variation in grade and size of ore body
unexpected geo conditions e.g. faulting
variations in economic climate and demand
improvement in extraction tech
life cycle of mine
stage 1- design and planning
stage 2- construction
stage 3- production
stage 4- processing
stage 5- rehabilitation and reclamation
design and planning of mine
assumes surveys done and assess grade + low cost processing
profit remitted- more likely to succeed if needs of locals are met
as benefits shared
rehab and reclamation are part of planning
construction of mine
(what do they build?)
extraction and
processing facilities and
roads and
enviro
management systems and
housing / other facilities
production in mine
may be open pit or underground
depends on depth and size of target body
and limits imposed by health and safety
as well as tech, enviro damage and economics
processing in mine
mineral materials sent through huge crushers or mills to sep commercially valuable from gangue/waste rock
means transport to smelter is more economic
rehabilitation and reclamation
once exhausted site is dismantled
and land is returned to og state
large open pit mine may mean this is impossible
aim is to insure public health and safety and minimise enviro impact by removing waste, hazardous material, preserving water quality, stabilise against erosion and establish new veg
types of mines
open pit/cast mine
stope mining
longwall retreat mining
open cast/pit mining
SEE BOOKLET FOR DIAGRAM
for ore close to surface
often more economical to strip away overlying by quarrying than building underground mine
open pit mining pros and cons
pros-
cheaper than underground
V efficient and high r of production
only small workforce
safter
no vent equip required
cons-
V bad for enviro
slope stability problems of central mounds
lower grade ore
stope mining
SEE BOOKLET FOR DIAGRAM
most productive to extract ore from ore body itself without need to construct additional shafts
exact methods depend on size and grade
lowers cavity
drills shafts straight down and then horizontal levels into ore body (usually have supports and may be back filled )
blast - break - fracture - extract - this is stoping
stope = cavity
Stope mining pros and cons
Pros-
less enviro issues and habitat loss
can access hard to access reserves
cons-
more expensive and technical
have to pay form ventilation + water pumping + backfilling pumps
subsidence risk
high e requirement
longwall retreat mining
SEE BOOKLET FOR DIAGRAM
main shaft dug from surface and tunnels drawn out from shaft
2 roadways drawn to furthest point of extraction asses geo condition prior to mining
longwall is established between 2 roadways
shaver moves along face slicing coal onto conveyer belt
roof held up by hydraulic steel chocks
once coal is removed chocks move forward and mined out area collapses
retreat towards shaft
pros and cons of long wall retreat
pros-
can achieve production rates comp to open cast
high vol of material
low enviro impact and habitat loss
cons-
high e requirements
high tech
expensive
leaching basic
uses chem sol to dissolve ore from the rock and release target minerals
2 types of leaching
in situ leaching at depth
heap leaching at surface
in situ leaching at depth
boreholes drilled
fracture rocks e.g. explosives
leaching sol pumped down
leaching sol containing ore pumped back up
e.g. evaporates extracted using h2o
U and Cu using acid
in situ leaching pros and cons
pros-
less people and machines (cheaper)
little disturbance
no waste
recycle leaching sol
cons-
toxic
heap leaching at surface
same as in situ but material brought to surface
crushed to increase SA then heaped on impermeable barrier e.g. clay
sol with dissolved mins accumulates in pond
taken for further processing
heap leeching pros and cons
pros-
cheap
60-70% extracted
recycle sol
cons-
takes a long time - months to years
froth flotation basic
separates hydrophobic and hydrophilic mins
process of froth flotation
ore and H2O = slurry
only works if target min hydrophobic
add chemical to make it hydrophobic
aerate slurry- add O2
hydrophobic minerals attach to air bubbles
rise to surface as froth
froth collected by skimming
rich in target min
e.g. produces 70% of the world copper
disposal of crushings and tailings post froth floatation
fine grained waste
contain toxic min and chems from extraction
prev, stored in large surface ponds or disposed of in in underground mines workings or river/sea
enviro disaster caused by leakage or may be unstable
now legally regulated
smelting - reduction of ores
specifically iron
sep using heat and reactivity series
blast furnace
used to extract iron (oxides)
carbon (in coal) for more reactive than iron
carbon removes O2 from iron - reduced
iron isolated
problems with mine water
Acid mine drainage
acid mine drainage
many mined minerals = sulphide ores
empty mines contain fractured rock - exposed/ large SA
empty mine is exposed to H2O and O2
react with ores to produce sulphuric acid
sulphide min + O2 –> SO2
SO2 + H2O —> H2SO4
treatment methods for AMD
source control
migration control
active treatment
passive treatment
source control for AMD
prevent O2 and H2O reaching ore
dewater mine- pump out H2O (expensive)
or flood and seal with e.g. concrete or clay
migration control for AMD
redirect to storage pond for further treatment
active control for AMD
adding something to react and neut
e.g. alkali - lime CaCO3 OR NaCO3
passive treatment for AMD
use nature based system e.g. trickle beds
trickle through limestone gravel to neut
microorganisms can consume toxic metals sulphides
what can be in underground waste storage
chemicals
animal carcasses
nuclear waste (diff level treated diff)
CO2
heavy metal waste
rubble-inert
municipal sewage waste e.g. collected by council
mining waste
industrial effluent+ agricultural waste
domestic waste
advantages and disadvantages of underground waste storage
Pros-
space efficient
reduces visual impact
quick and easy
low tech requirements
cheap
resists structural damage e.g. earthquakes
Cons-
public opp
limited capacity
leachate toxic to soil and water bodies
produces methane- greenhouse gas and explosive
prone to subsidence
factors effecting severity of enviro consequence of underground storage
leachate- rain h20 peculates through waste
dissolves soluble chems/mins
surrounding soil and h20 in aquifers are vulnerable to contam
forms pollution plume
rock type- impermeable and fine grain e.g. clay resists leachate
thick uniform flat beds=best
permeable and porous allows leachate to flow
limestone dissolved by acid
met and ig best only if jointed secondary permeability
anticlines- tension joints - increase permeability
groudwater- higher WT less distance for leachate to travel to reach underground water
levels of nuclear waste
low
intermediate
high
transuranic
low level nuclear waste
90% of waste by vol
gloves and clothing
dep at secure landfill sites
grouted in metal containers and super compacted then stacked in concrete lined vault, cap covers when vault is filled
some landfills can except V low levels of radioactive waste
looking at alt methods e.g. incineration and metal recycling
intermediate nuclear waste
7% of waste by vol e.g. reactor comps, graphite from cores
cutting, drying and super compacting
place waste in suitable container e.g. 500l stainless steel drums
immobilise water in cement based materials
placed in underground facility or repository
geological structure prevents escape of radioactivity
or near surface disposal- disposed of close to site as pos
high level nuclear waste
3% by vol
spent nuclear fuel
vitrification-liquid HLW mixed with crushed glass in furnace poured into stainless steel canisters which hold up to 150L
creates solid stable product for long term storage
held for 50years then dispose of at repository again geological disposal- geo structure insures no radioactivity escapes
transuranic
heavy unstable atoms anything above U-92
features of underground nuclear disposal site
hard competent rock
few faults and joints
little seismic activity
low WT
problem with CO2 + where it anthropogenic emissions come from
acts as greenhouse gas and may lead to acidification of the sea
by burning
processing fossil fuels
manufacturing steel, cement and chemicals
how can we prevent CO2 entering atmosphere
carbon capture and sequestration- stored underground
react CO2 with metal ions (carbonation)–> form new metal carbonates (stable) –> store
capture and compress –> transport via pipelines to underground to depleted gas fields and oil fields
saline formations- dissolve C02 combine with rock forming new stable mins
examples of carbon capture, storage and sequestration
forest
soil e.g. peat bogs
ocean
graphene production-
requires CO2
engineered molecules-changes shape of mol to form new compounds by capturing CO2
grasslands
direct air capture
biomass carbon removal/capture- use biomass from plant to remove CO2 from air e.g. biooil, biochar, bioenergy
carbon mineralisation
where is chalcopyrite often found
often found in hydrothermal veins
