Download Mineral resources 3

Mineral resources 3
Immiscible separation
• Nickel-copper deposits from at
the end of liquid immiscibility
• Cooling magma can separate
into silicate-rich and sulfur rich
liquids
• Do not mix – are immiscible –
therefore separate out into
distinct liquids
Immiscible separation
• Sulfur-rich liquid is heavier than silicate rich liquid – sinks to
bottom of intrusion
• Minerals such as pentlandite and chalcopyrite (Ni and Cu
rich) crystallise out from cooling sulfur-rich liquid at base of
intrusion
• Magmatic Ni-Cu deposits found at/near base of layered
intrusion, stocks and ultramafic sills
• Largest deposits in Australia: komatiitic volcanic sills within
Archean greenstone belts at Kambalda and Mt. Keith in WA
http://pubs.usgs.gov/of/1995/ofr-95-0831/CHAP4.pdf
Nickel
•
Igneous rocks – made from ultramafic lava flows and intrusion (high Mg, Fe and Ni
content)
•
Two processes for formation of nickel – gravitational settling and immiscible
separation
•
GS – early formed heavy minerals e.g. Ni, will settle to bottom of lava
flow/intrusion
•
IS – based on concept of oil and water – silca rich and sulfide rich magmas do not
mix readily. Nickel minerals are concentrated in the sulfide rich magma (could be
in pockets or settled to the bottom of cooled magma)
•
Found in Kambalda, near Kalgoorlie and in ultramafic rocks
•
Ultramafic rocks are over 2 billion years old from a time when the mantle was
hotter
Coal
Coal
• Vegetation/plant matter that has been buried
quickly e.g. swampy areas for some time
• Type of coal depends on temperature and
pressure p441 for table
• Coal is found in Collie
Parameters of coal quality:
• Moisture
– Water in porous spaces – energy required to drive off water
– Impact on thermal “quality” of coal
• Ash
– Incombustible residue after burning
– Higher ash content = longer burning time and larger combustion
chambers
– Ash causes erosion of flues and induced draft fans
• Volatiles
– Components driven off by heading such as CO2, methane, water, sulfur
dioxide and nitrous oxide.
– Presence of organic volatiles is important for the ease of coal
combustion in the power station boiler as >20% ensures coal ignition
• Fixed carbon
– Carbon left after moisture, ash and volatiles removed
– Oxidation of carbon is what produces steam > drives turbine> energy
Colour
Water
content (%)
Other
volatiles (%)
Fixed
carbon (%)
Approximate heat
value (BTU’s of heat
per pound of dry
coal
Peat
Brown
75
10
15
Varies
Lignite
Brown to
brownish
black
45
25
30
7000
Subbituminous
coal
black
25
35
40
10000
Bituminous
coal
black
5-15
20-30
50-75
12000 to 15000
Anthracite
(hard coal)
black
5
5
90
14000
Coal
• Formed from sedimentary rock – compaction of plant
materials that have not been completely decomposed
• Mixture of organic (carbon-based) substances, water
and mineral matter
• Common minerals include quartz, kaolinite (clay),
siderite and pyrite
• Geological settings determine quality of coal produced
The Collie Basin, WA
• Sub-bituminous coal deposits built on layers of sandstone
about 160 million years ago
• High quality coal due to geological setting – no methane
and low levels of sulfur and ash. Also highly reactive
• Contains low levels of mercury and selenium make good for
domestic use
• Now primarily used for power generation, mineral
processing, cement manufacture and as a pure heat source
Questions
1. What type of rock does coal form from?
2. Name two common minerals found in coal
3. What are the main parameters that decide the quality of
coal?
4. What factors reduce the rate of decomposition in organic
matter to increase carbon percentage?
5. What type of geological setting results in higher quality coal?
6. Where in WA is coal found?
7. Why is Collie so good for coal?
Answers
1.
Sedimentary rock
2.
quartz, kaolinite (clay), siderite and pyrite
3.
Moisture, ash, volatiles and water
4.
Organic matter must collect in water-logged environments that will stop destruction and
dispersal through bacterial decay. The environment is usually one of shallow surface water
and organic matter that is sustained over long periods of time.
5.
Geological settings characterised by stagnant waters that limit dead plant material
exposure to oxygen, therefore reducing decomposition rate. This allows plant matter to be
buried completely before it breaks down
6.
Coal is found in Collie in WA (know where it is on the map!!)
7.
High quality coal due to geological setting – no methane and low levels of sulfur and ash.
Collie coal is also highly reactive and contains low levels of mercury and selenium make
good for domestic use
Oil and Gas
Oil and Gas
• Found in Barrow Island or North West Shelf
• Geological setting is mostly ocean
Oil and gas terminology
• Crude oil – a liquid of naturally occurring
hydrocarbons that can be refined to produce a
large number of products
• Natural Gas – a gaseous mixture of naturally
occurring hydrocarbons. It is usually associated
with the occurrence of crude oil
• Hydrocarbons – chemical compounds containing
both hydrogen and carbon
Oil and Gas
• Large amounts of organic matter (largely plankton) die and buried
under sediments where there is a lack of oxygen
• Depth of burial for for oil 3-4.5kms
• Depth of burial for gas 4-6kms
• Formation over millions of years at right temperatures and
pressures
• Plankton turns into keragen then finally oil and gas (optimal temp
and pressure)
• Oil and gas hosted in sediment e.g. sandstone – fills pore spaces,
not in pockets!
• Will eventually seep out on to ocean bed
• Impermeable rock is called a seal that stops this from happening
• Other geological structures that do this are called traps
Oil and gas formation
•
https://www.youtube.com/watch?v=8YHsxXEVB1M
•
Plankton turns into keragen then finally oil and gas (optimal temp and pressure)
•
Oil and gas commonly accumulate in sedimentary rocks
•
Organic matter formation in sediments that settle on sea floor – become part of
marine mud
•
Decomposition of organic matter will eventually stop when all oxygen has been
depleted
•
Deposition of sediments continue, burying organic matter further
•
Temperature and pressure will increase – oil and gas droplets can be squeezed out of
mud and into sandy rocks with greater porosity and permeability
•
Oil and gas pools or reservoirs gradually form in sandy rocks (pore spaces, not
pockets!)
– Oil and gas less dense than water so they tend to rise up and be trapped if the rocks about have no
porosity and permeability and form a seal
Progressive Burial and Heating
Schematic Representation of the Mechanism
of Petroleum Generation and Destruction
Organic Debris
Diagenesis
Oil Reservoir
Kerogen
Initial Bitumen
Catagenesis Thermal Degradation
Oil and Gas
Cracking
Metagenesis
Carbon
(modified from Tissot and Welte, 1984)
Methane
Migration
Oil and Gas
Task:
• Summarise the formation of oil and gas (p444-445)
What is a Trap
• A trap is the place where oil and gas are barred from further
movement….(Levorsen, 1967)
.
Seals or Cap Rocks
• For a trap to have integrity, it must be overlain by an effective
seal.
• Any rock that is impermeable can act as seal or cap rock but
commonly mudstone
Oil Traps
• Some rocks are permeable
and allow oil and gas to freely
pass through them
Impermeable
• Other rocks are impermeable
and block the upward passage
of oil and gas
• Where oil and gas rises up and capped
by impermeable rocks it can’t escape.
Permeable
•This is one type of an Oil Trap.
Reservoir Rock
• The permeable rocks than
contain oil and gas within
the oil trap are known as
the Reservoir Rock.
• Reservoir rocks have lots
of interconnected holes
called pores. These allow
them to absorb the oil
and gas like a sponge.
This is a highly magnified picture of
a sandy reservoir rock
As oil migrates it fills up the pores
(oil-filled pores shown in black)
Earth Science World Image Bank Image #h5innl
Exploration for oil and gas
Read pages 447-448 and summarise the exploration process
Use the key words listed below to help you:
• Lead
• Play
• Dry hole
• Bright spot
• Prospect
• Chance or probability of success
• Hydrocarbon in place
• Recoverable hydrocarbons
Visible surface features
Hydrocarbon seepage
Most already discovered
Exploration geophysics
Gravity, magnetic or seismic surveys conducted
Detection of sub-surface geology
Identifying features of interest
Leads subject to more detailed seismic surveys
Time taken for sound waves to be reflected indicates density –
profile creation of substructure
Exploration well drilling
Prospects that have passed economic risk selection
criteria are drilled – exploration well
Core samples studied
Samples containing oil will fluoresce under UV light
https://www.youtube.com/watch?v=SfazJ6P_g7w
Drilling for hydrocarbons
•
Well drilled deep into Earth using a
rotating bit attached to a hollow drill
pipe
•
Hole forms in the ground – deep it gets,
more pipe is added
•
Drilling mud is continuously pumped
through drill pipe to cool rock walls and
prevent cave ins by forming a “mud
cake” on sides of hole
•
When oil/gas is found, drill pipe and bit
removed and metal pipe called casing is
cemented into place
•
Upper end of casing fastened to a system
of pipes that separates oil and gas for
storage and transport
Natural Gas
• Also discovered through exploration of sedimentary basins
• Not always found with oil reservoirs
• Important resource but costly and difficult to transport – liquefied natural
gas (LNG) is the solution
• LNG is gas that has been cooled to a temperature where it becomes a
liquid
• Occupies less volume, is colourless, odourless and not corrosive or toxic
. Suggested to be the cleanest fossil fuel
• LNG important to WA – construction of Pluto and Gorgon currently under
way.
• In addition to North West Shelf Venture, WA is one of the most important
LNG producing areas in the world
Refining
• Refers to the transformation
of crude oil and condensate
into end-use petroleum
products.
• State’s oil refinery owned
and operated by BP and
located in Kwinana
Other non-renewable energy
• Nuclear energy generated by fission or fusion.
• Nuclear fission – atoms are split to form smaller
atoms and release energy. Nuclear power plants
do this
• Uranium is commonly used for nuclear fission
and is mined in WA
• Nuclear power is heavily debated in Australia –
currently no nuclear facilities despite having
23% of the world’s uranium deposits.
• Second largest producer behind Canada
Oil shales, oil sands
•
Oil shale – sedimentary rock containing solid bituminous materials (kerogen) that is
released as petroleum-like liquids when rock is heated (pyrolysis)
•
Process of formation is similar to oil, but with less heat and pressure
•
Extraction process is more expensive
•
Mostly found in Eastern States but currently not economically viable for mining
Oil shales, oil sands
• Oil sands also known as tar sands are a type of bitumen
deposit
• Naturally occurring mixture of sand/clay and water –
extremely dense and viscous form of petroleum called
bitumen
• Canada has the largest quantity
• No known economically viable sources in Australia
Iron formation
Sedimentary Ores
• Banded iron formation (BIF) results from
precipitation of metals transported in solution
• Chemical precipitates is a term that refers to
mineral deposit in which large quantities of
metals were transported in solution to place of
deposition and precipitation
• Iron, lead, zinc, manganese and uranium ores
are formed in this way
Banded Iron Formations
• Iron ore minerals that are examples of BIFs – hematite
and goethite
• Rocks are deposited as chemical precipitates on the floor
of shallow ocean basins in highly oxidised environments
• Individual deposits normally tens of km long, several kms
wide and 150-600m thick
• Very old! 2000 million years old and found in The Pilbara,
WA
• Deposits provide evidence for evolution of life and the
atmosphere
Banded Iron Formations
• Ores typically alternating layers of iron rich minerals
and chert (quartz containing small amounts of iron
oxide)
• Iron mineral bands may be composed of hematotite,
magnetite, siderite or pyrite
• Particular iron minerals indicate chemical conditions
of sedimentation e.g. oxygen availability
• Much later, weathering can cause the dissolving out of
silica from chert, increasing the concentration of iron –
higher grade ore results
Read and
summarise the flow
diagrams on page
107 – How BIFs are
formed
Trilobites
• Most diverse creatures in Lower Paleozoic
• Named after their structure
• Extinct now, but evidence from fossils
reveals:
– Bottom dwelling marine creatures
– Wide geographical distribution in Western
Europe, Australia and East Asia
– Evolved distinct characteristics in short
periods of time – comparison between age
of strata and location makes them good
index fossils
Stromatolites
•
Considered to be the oldest evidence for life on Earth
•
Found in sedimentary rocks 3400 years old near North Pole
mining camp in The Pilbara
•
Made by a combination of physical processes and microorganisms
•
Algae and bacteria trap and bind sedimentary particles to
form distinctive cabbage shaped mounts with layers of
calcium carbonate and pother sediments
•
Click here for how stromatolites caused BIF (also p107 flow
diagram)
•
http://www.geologyforinvestors.com/banded-ironformations-bif/