6. Lithosphere

• Rocks are a combination of different minerals
• Minerals are naturally occurring concentrations of materials (solid, liquid or gas) in or on the earth's crust
• Mineral resources are extracted and processed (if necessary)
• Fossil fuels

  • Natural gas
  • Coal
  • Crude oil
• Metal ores

  • Chalcopyrite: copper
  • Galena: lead
  • Magnetite: iron
• Non-metal ore

  • Limestone
  • Slate
  • Granite
• Sedimentary process - Alluvium

  Soil or sediment deposited by the flooding of a running water source e.g. sand, gravel
• Sedimentary process - placer deposits 


  Deposits formed by the slowing of water where rivers bend. Often heavy sediments are dropped e.g. magnetite, gold and platinum
• Sedimentary processes - evaporites 


  water soluble mineral sediments that result from the evaporation of bodies of water on the earths surface, such as the dead sea. e.g. gypsum
• Sedimentary processes - biological deposits

  • Shells -> chalk
  • Plants -> coal
  • Marine animals -> oil
• Sedimentary processes - Protozoic marine sediments

  sediments formed in the proterozoic period. The minerals formed have been oxidised within these sediment layers, making clear deposits
• Sedimentary processes - Secondary enrichment

  an ore concentrating process when surface rocks are leached below the water table, where reducing reactions form insoluble deposits
• Igneous processes - Hydrothermal Deposits 


  Metallic element dissolves into the hydrothermal liquid and is transported through the crust. As the hydrothermal solution cools metals become less soluble and precipitate out 
• Metamorphic Processes 


  Igneous or sedimentary rocks are subducted down back towards the mantle where the extreme heat and pressure alters their chemical and physical properties e.g. slate, marble
• Mineral Stock 


  All minerals that exist in the lithosphere. Including the minerals that can be exploited now, will be exploitable in the future, and those that can never be exploited.
• Resource 


  All the material that is theoretically available for exploitation. This includes deposits which are, at present, un-economic to be exploited
• Reserve


  The proportion of the mineral resource that can be exploited now, economically, using existing technology
• Inferred reserve 


  The presence of the mineral is predicted from knowledge of the geological structures present, but not enough is known to estimate the amount that can be economically extracted
• Probable reserve 


  Sufficient information about the deposit is known, so the amount of mineral that can be economically extracted can be estimated with sufficient accuracy that further exploration is justified
• Proven reserve 


  Sufficient exploration has been carried out, including trial drilling, to accurately estimate the amount of mineral that can be economically extracted
• Lasky's Principle 


  As the purity of a mineral decreases, the amount of mineral present increase exponentially. Therefore, exploiting low quality ores is more important to future mineral supplies that the quantity of minerals available.
• IR spectroscopy 


  Different minerals emit infrared radiation at different wavelengths and these can be used to identify them
• Gravimetry 


  Gravimeters detect variations in gravity caused by variations in density and mass. Igneous rocks are usually more dense than sedimentary deposits.
• Magnetometry 


  Magnetometers detect rocks that are more magnetic such as iron ore magnetite and ores of tungsten and cobalt
• Seismic surveys 


  These involve sound waves produced by controlled explosions, or a seismic vibrator on the surface. The echoes can give information about the depth, density and shape of deposit
• Resistivity 


  Resistivity is the measurement of the difficulty with which electricity passes through a material. In general, sedimentary rocks have lower resistivities than igneous rocks because they have higher water contents
• Trial drilling 


  The most expensive technique per sampling site but it is the only method that actually produces samples of the rocks underground
• Chemical analysis 


  Laboratory tests confirm the chemical composition and purity of the minerals in the rock samples
• Ore purity 


  The purity of the ore affects the financial costs of exploitation and the environmental impacts of mining. If the ore grade is low then:

  • More rock will have to be mined
  • More waste materials will be produced
  • More energy will be needed for mining and processing
  • More pollution will be generated
• Chemical form 


  The chemical form of the mineral ore affects the ease of chemical extraction of the metal. For example, aluminium can be extracted from bauxite (aluminium oxide) but not from clay which is more abundant.
• Overburden and hydrology 


  The overburden is the rock that lies above a mineral deposit. Hard overburden may require blasting which increases costs. Loose overburden may increase the risk of landslides. Higher precipitation or impermeable rocks below may increase drainage costs.
• Depth 


  Cost rise as the depth increases. If the depth is doubled then the cost will also doubles. The sides of the mine cannot be vertical because of the risk of collapse.
• Cut-off ore grade 


  Mining has to be an economically profitable activity, so there must be a balance between production costs and income. The lowest ore purity that can be mined economically, using existing technology is called the cut-off ore grade (COOG). The COOG changes as technology improves and the market prices fluctuate.
• Transport costs

  Affected by the distance to market, the ease of bulk transport, the presence of a suitable existing transport infrastructure and whether the bulk of the mineral has been reduced by processing
• Market economics 


  The market demand and sale value of the minerals control the economic viability of exploiting a specific mineral deposit. price is controlled by the demand for the mineral
• Exploration 


  Marine seismic surveys cause load vibrations. Land exploration involves land clearance and vegetation loss.
• Land take 


  Conflicts with existing land use. Mines take up a large area and can only be placed where the minerals are. Land is needed for associated buildings, access routes, overburden dumping and "buffer" zones
• Habitat loss 


  Loss of species natural habitat. Capture and transfer of animals and plants to threatened habitats (rarely successful). After mining has finished, habitats can be restored in the destroyed area.
• Loss of Amenity 


  Mines, associated buildings and spoil heaps often cause aesthetic problems for local communities
• Pollution 


  Dust, noise, turbid drainage water, toxic leachate and spoil disposal