Geological Processes

Geological Processes

1. Igneous processes

   • Rocks and minerals are created by the cooling and hardening of magma or molten lava.
   • Eg. hydrothermal deposition
     • 1. Igneous intrusions are rocks formed from magma that cools and solidifies within the Earth's crust.
     • 2. The intrusions produce pressurised superheated water at high temperatures that dissolves many minerals from the surrounding rocks.
     • 3. These mineral-rich solutions travel along fissures away from the igneous batholith, cooling as they do so.
     • 4. As they cool, dissolved minerals crystallise and come out of solution in order of solubility.
     • 5. This process of fractional distillation separates and deposits the minerals, allowing them to be exploited.
   • Metal ores deposited by this process include: tin, copper, lead, silver, gold and arsenic.

2. Metamorphic processes

   • For example
     • High temperature and high pressure can convert limestone into marble.
     • High pressure can convert mudstone into slate.
   • Can be triggered by igneous processes and tectonic movements.
   • Metamorphic rock forms under high temperature and high pressure, without the rock melting.

3. Sedimentation processes

   • 2. Alluvial deposits
     • Materials are carried and separated by flowing water based on the velocity of the water and the density of the solids.
     • Eg. gold, diamonds, tin ore, gravel, sand and clay
   • 1. Proterozoic marine sediments
     • Including iron deposits that were formed when dissolved iron was first oxidised by oxygen released from photosynthesis millions of years ago.
   • Cause minerals to settle and accumulate to produce layers of deposited sediment.
     • Thus creating sedimentary rock.
   • 3. Evaporites
     • Form when an ancient sea is isolated and water evaporates, leaving crystallised minerals.
     • Also form in inland seas in deserts, when inflowing water from rivers evaporates.
     • Eg. sodium chloride
   • 4. Secondary enrichment
     • Many metals form minerals that are soluble and insoluble depending on the conditions.
     • When conditions change, a mineral may become insoluble and thus be deposited.
       • This frequently happens due to the availability of oxygen, which alters a mineral's oxidation state.
   • 5. Biological sediments
     • Biological processes where living organisms form mineral deposits.
       • Often concentrate minerals that can be deposited in sedimentary rock.
       • For example
         • Shells of marine organisms form limestone and chalk
         • Terrestrial vegetation forms coal
         • Marine organisms form crude oil and natural gas