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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/