6: The lithosphere Flashcards
Define igneous, sedimentary and metamorphic rock
Igneous: Formed through the cooling of magma
Sedimentary: Formed when sediment is compressed under lots of pressure to form rocks like sandstone.
Metamorphic: When rock is changed under significant heat and pressure
What is an Ore?
A rock or sediment with a significant percentage of valuable metals/minerals.
What are hydro-thermal Veins?
Veins of valuable minerals/metals have been deposited and crystallised out of solution.
outline how are hydro thermal deposits made?
1) An intrusion of cooled magma brings sparsely concentrated ores and minerals towards the surface.
2) Rain percolates down towards the intrusion and dissolves the minerals and metals into solution
3) The heat causes the water to expand and force up into the cracks
4) Overtime the minerals and metals crystallise, creating large streaks of valuable mineral deposits
What 4 sources are sedimentary deposits made from?
- weathering of rocks
- weathering and oxidation of former minerals/metal deposits
- some may have passed trough an internal biological stage
What are Proterozoic marine sediments?
They are vitally important iron ore deposits, which become oxidised when life began to photosynthesise and release fast amounts of oxygen .
This can be seen in some rock cliffs that have been oxidised red half way through.
What are alluvial deposits?
Deposits made out of sand, gravel and valuable materials that flow in streams.
What are evaporites?
Crystals made by evaporation from an aqueous solution of minerals. Usually created when lakes dry up.
What are biological sediments?
sediments made from eroded/ decayed organisms to create materials like chalk (sea shells).
What is ore cut off grade?
The minimum grade required for the ore to be economically mined.
What are (mining) reserves?
The amount of material that can be exploited using existing technology under current economic conditions.
What are (mining) resources?
All the material that could potentially exploited technically and economically now or in the future.
What is laskys law?
Shows that as the decrease the ore cut off grade, the amount of material included is increased.
What are the names of the different survey techniques?
- gravimetry
- Magnetic methods
- Electrical resistivity
- satellite imagery
What is gravimetry?
A technique which measures variations in the earths gravitational field.
These variations are caused by density contrasts in the surface rock and sediment.
Geographical surveys are performed with gravimeters and are always accompanies by high precision topographic surveys.
What are magnetic geology survey methods?
Aircrafs/vehicals with recording instuments often travel over the intended area and detect changes to the earths magentic feild. Often used to dect metals such as iron.
What is involved in the electrical resistivity survey technique?
Injection of current into the ground to detect the electrical resistance felt, which directly links to the density of the rocks.
What is satellite imagery surveying?
When satellites send radiation such as visibile light, Infrared and uv rays to earth, to map the different minerals.
What is a mines overburden?
The rock/material above the ore.
What factors effect mine viability?
- overburden
- hydrology
- ore purity
- depth
- transport/accessibility
- economical viability
What is systematic trial drilling?
A representative sample of rock needs to be taken so that the mining company knows which areas can be commercially exploited, and which areas have highest ore purity.
Name 5 environmental impacts of mineral exploitation.
- carbon dioxide emission
- landscape scarring and degradation
- destruction of habitats
- chemical leachate (leaking)
- deforestation
When are the two different types of used?
Open-cast mining
- Used when there are relatively large deposits that are quite close to the surface.
- usually cheaper, but creates a lot of waste
Deep shaft mining
- mine deep deposits
- more precise, so can afford to mine smaller deposits
What is tailing?
It the waste powder created when ore is processed. In most cases this is toxic and is stored in a tailings pond.
What are two potential impacts of sand mining?
- Sand stores water underground in arid regions, meaning if the sand its taken away, then the impermeable bedrock is left and water runs off.
- can cause erosion of beaches and river banks
- if water runs off quickly, lakes can begin to dry up, impacting the local fishing industries.
Link one named resource to its geophysical technique
- Magnetism of iron ore/magnetite Magnetometry
- High density of igneous deposits/galena/cassiterite Gravimetry
- High electrical resistance of igneous deposits Resistivity
