Geological processes/mineral formation

• Sedimentary - minerals are formed from the pressure created by layers of minerals above it. Water is involved.
• Alluvial deposits - river flooding

  • When a river floods the sediment it is carrying is taken onto the banks
  • When the water flow decreases again the minerals are deposited on the banks
  • This builds up over time and can be mined
  • e.g. silt, sand and clay
• Types of sedimentary

  • Alluvial deposits
  • Placer deposits
  • Evaporites
  • Biological deposits
  • Protozoic Marine Sediments
  • Secondary enrichment
• Placer deposits - river bends

  • The flow of the river slows around a bend and minerals in the river are deposited
  • e.g. gold
• Evaporites - evaporation

  • Water evaporates and sediment is left behind
  • This builds up over time
  • The minerals that are left are called evaporites
  • e.g. salt - sodium chloride
• Biological deposits - living matter

  • made from living matter that has anaerobically decomposed and been compacted
  • Plants to coal
  • marine creatures to oil
  • Shells to chalk
• Protozoic Marine Sediments - a period of time when photosynthetic bacteria/archea evolved

  • Bacteria evolved that could photosynthesise and produce oxygen
  • This oxygen reacted with marine sediment like iron until all the mineral was oxidised, the oxygen built up in the atmosphere
  • mineral deposits have a high amounts of oxygen
• Secondary Enrichment - ore purifying process

  • low grade ore becomes purer
  • occurs when the mineral deposit goes below the water table
• Maturation - marine organisms become oil
• Coalification - plants anaerobically decompose and are compacted to form coal
• Igneous - lava and magma form mineral deposits
• types of igneous:

  • intrusive deposit
  • Extrusive deposit
  • Hydrothermal deposits
• Intrusive deposit

  • formed from the cooling of magma underground, very slowly. Therefore minerals have a long time o form large mineral deposits
  • e.g. granite
• Extrusive deposits

  • formed from the cooling of lava on the surface, so it cools very quickly making the mineral deposits small
  • e.g. basalt
• Hydrothermal deposits

  • Hot water deposits
  • water in an aquifer is heated by magma
  • Minerals dissolve into the water
  • Due to thermal expansion of the water fissures (cracks) form
  • Water cools in the the cracks and minerals precipitate/crystallise out of the water
  • Due to differing crystallisation points different minerals crystallise out at different times creating high purity deposits formed as veins of ore
  • e.g. tin ore
• Batholith - an extrusion/bump in the ground formed by hydrothermal deposits
• Chemical precipitates - minerals crystallise out of the hydrothermal fluid when it cools
• Metamorphic - pressure and heat

  • extreme pressure and heat changes the compounds of the mineral into a different mineral
  • example: marble, slate
• Denudation - weathering breaks down rocks