Extraction of Rocks and Minerals

• Minerals provide us with a wide range of materials we use everyday

  • coal & oil - energy and many chemicals used in industries
  • metallic ores - metals and alloys to make computers, phones, cars etc.
• Prospecting - a process of finding mineral deposits

  • found by looking at the surface of rocks
  • this method found nearly all surface mineral deposits
• Ore - a rock with an important element to make it worth mining
• Remote sensing - information is gathered about the Earth’s surface from above

  • it covers more ground that someone walking over the surface of rocks
  • helps find mineral deposits by photographing an area from the air and then analyzing the images
  • images and data from satellites can help to analyse large areas
• Mineral deposits are weathered by the Earth’s surface, creating mineral oxides

  • allows for detection from radiation pattern, recorded by a satellite, and downloaded by a computer for analysis
• Satellites can operate by sending signals to the surface of the Earth, collectiing reflected signals

  • works in all weathers - clouds, night time
• Mineral ores in rocks below the surface can be located by satellite images

  • computers process data from a region of interest to see if minerals are present
  • satellite’s positioning system record the exact location
  • geologists visit the location to confirm that minerals are there + check further locations to see if other minerals are nearby
• Satellites can map large areas quickly and at a low cost
• Field surveys - takes samples and sends them to a laboratory for geochemical analysis, chemicals cna be identified

  • samples can be taken from stream sediments, soil or rocks (using shallow drilling)
  • points where samples are taken are selected by using a grid on the map of the survey area and then accurately found by the GPS
• Geochemical - chemical properties of a rock
• • Geophysics - method to identify mineral ores in rocks using their physical properties (explosives can be used but more dangerous)
  • A series of vibrations (seismic waves) are sent through the Earth’s surface
  • Several sensors are placed at different distances from the source of vibrations on the ground
  • The vibrations create shock waves that travel down into the rock layers
  • The waves are reflected back to the sensors on the surface
  • The shock waves record different patterns depending on the minerals present in the rock layers
• Geophysics diagram

  A) sensors pick up reflected wave

  B) collects information from sensors

  C) seismic shock waves

  
• Geophysical - physical properties of rock
• Two main methods of extraction

  • Surface mining - a type of mining used when the mineral is either exposed on the surface or overlain by only small amounts overburden
  • Sub-surface mining - a type of of mining used when the deposit is covered by a deep layer of unwanted rock
• Types of surface mining:

  • open-cast/open-cut/open-pit mining
  • strip mining
• Open-pit/ open-cast/ open-cut mining is used when a valuable deposit is located near the surface, buried under overburden (1)

  • overburden is removed first (vegetations & topsoil) to expose the deposit and stored nearby for restoration
  • dug in sections aka benches - the walls are kept an angle to prevent rock falls and this angle depends on the type of deposit and overburden
  • roads are made to allow transportation of minerals and overburden
• Open-pit/ open-cast/ open-cut mining is used when a valuable deposit is located near the surface, buried under overburden (2)

  • rocks are broken up and loosened with explosives
  • rock is removed using digger
  • rock or mineral is tipped into trucks or railway wagons
  • building materials e.g. sand, gravel & stone are removed from quarries (open pits)
• Open-pit/open-cast/open-cut mining diagram

  A) benches

  B) overburden

  
• Overburden - the rock and soil overlying an economically viable mineral deposit
• Two reasons open-pit mines will stop being worked:

  • as much of the valuable deposits have been removed
  • amount of overburden that needs to be removed has increased to the point that the mine isn’t profitable
• Strip mining is used to mine a seam of mineral

  • overburden (the unwanted overlying rock and soil) is removed as a thin strip
  • mainly used to mine coal and lignite
• Types of sub-surface mining

  • deep mining
  • shaft mining
• Sub-surface mining - digging tunnels into the ground to reach mineral deposits that are too deep to be removed by surface mining (1)

  • A horizontal tunnel can be dug directly into the coal seam in the side of a hill or mountain aka a drift mine entered by an adit
  • produce waste rock and mineral ore
  • Sloping tunnels are dug to reach deeper deposits and mining machinery are lowered down the sloping tunnels
  • waste rock and mineral ore are hauled up to the surface
• Sub-surface mining - digging tunnels into the ground to reach mineral deposits that are too deep to be removed by surface mining (2)

  • Deepest deposits are reached by digging a vertical shaft
  • more expensive and technically challenging than hororizontal or slope tunnelling so only large deposits are mined this way
  • Most material is removed from mines by machines and miners oversee the machines
• Sub-surface mining diagram

  A) drift mine with a horizontal entrance

  B) adit

  C) sloping tunnel

  
• Any form of shaft mining is more difficult than open-pit

  • lack of fresh air
  • lack of water drainage
  • risk of collapsing tunnel
  • risk of poisonous gas
  • explosion
  • underground fire
• Adit - entrance to a horizontal (drift mine)
• Factors affecting decisions to extract rocks and minerals:

  • climate
  • costs of exploration and extraction
  • geology
  • accessibility
  • environmental imapct
  • supply and demand
• Strike rate - the frequency with which attempts to find a mineral are successful
• Climate:

  • Have to consider what type of sites to work on
  • Green field sites - areas that have never been mined for minerals
  • chances of finding a deposit are low
  • for some metal ores, the strike rate is low e.g. gold
  • Brown field sites - areas that have been mined for minerals
  • have higher strike rates than greenfield sites
  • even low grade deposits may have enough value to be mined for profit
• Costs:

  • cost of extracting one tonne of ore has to be considered
  • surface deposits is lower in cost as open-pit mining can be used which is less technical
  • deeper deposits are higher in cost as it can only be extracted via shaft mining which is more costly to set up and maintain - only for deposits of high value
• Geology (1):

  • Quality is important
  • High-grade ores yield more of the required chemical elements than low-grade ores
  • Size is important
  • Small deposits of high-grade ores are worth mining
  • Small deposits of low-grade ores that cannot be mined at a profit are left as known reserves - may be mined in the future when technical advances make it less costly or increase in world price
• Accessibility (1):

  • Costs of building & maintaining road or rail links to the processing plant or the nearest export port must be considered
  • large tonnages - rail transport is the only practical & cost effective method of moving the ore
  • exported ore - large ships aka bulk carriers an keep transport costs low
  • carrying out processing of the ore at the mine can reduce transport costs by concentrating the mineral ore and separating it from waste materials - higher grade ore, higher value per tonne
• Accessibility (2):

  • Transporting the ore from the mine to processing plants can be difficult and expensive - can prevent a deposit being mined
  • Mining companies must be given a licence before extracting a deposit
  • Long-term agreement between the government and mining companies must be reached to avoid rapid rises in the tax, which makes mining unprofitable
• Supply and demand - the relation between how much of a commodity is available and how much is needed or wanted by the consumers:

  • An increase in world demand for any mineral ore will elevate the prices
  • The profit from a working mine depends on changes in supply and demand
  • If the demand is too high, mines that were not profitable before becoming worth mining
  • saving money on starting up a new mine
  • If the demand falls, new mines may lose profit due to the transport and extraction expenses
  • Companies try to predict future demand so they can still function in low-levels of profitability
• Global recession of 2008 stopped known mineral reserves from being mined because of reduced world prices
• Methods of looking for mineral deposits:

  • prospecting
  • aerial photography aka remote sensing
  • field survey aka geochemical analysis
  • geophysical analysis
• Geology (2):

  • Working life of a mine
  • depends on the size & planned rate of extraction
  • a mine with short working life means that ore value has to be considered if its necessary to mine there
  • a mine with long working life has less obstructions from other factors
  • Position of the deposit
  • Deeper minerals will use sub-surface mining vice versa
  • if the mineral is in strata, the size of the strata may impact the ability to develop tunnels
  • the stability of the rock will affect the choice of method used
• Environmental impact:

  • For the license application to be approved, the company must have a plan to keep the loss of habitat minimal, followed by the restoration of land and the completion of mining
  • The choice of site for mine waste should also be considered
  • The amount of environmental impact based on the type of mining need to be considered
  • surface mining - more impact
  • sub-surface mining - less impact
• Evaluations are carried out to see if the deposits of minerals are large enough to be mined, this is done by drilling

  • identifies the size and the mixture of minerals present
  • helps classify the deposit based on grade
  • small deposits - only a few samples are needed
  • larger deposits - more drilling is required
  • Information from evalutions can make a mineral deposit be classified as a reserve
  • Studies have to research the financial and technical risks of the mining project to get the final decision