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Geology A Level > METALS > Flashcards

METALS Flashcards

1
Q

Concentration factor

A
  • the number of times a metal is concentrated above the average crustal abundance

grade - % of metal in an ore
cut off grade - minimum % of metal for an ore to be economic to mine
concentration factor = cut off grade / average crustal abundance

  • cut off grade may change due to supply, demand, extraction methods
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2
Q

Hydrothermal veins

A
  • form during late stage cooling in silicic intrusions
  • hot water containing dissolved metal sulphides (immiscible to silicates)
  • Water moves out along joints into cooler country rock
  • Water cools and minerals precipitate to form mineral veins, containing ore and gangue

High - low melting point:
Tin, Copper, Lead, Zinc

diagram 19

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3
Q

ore, ore deposit, ore mineral and gangue mineral

A

ore - rock that contains valuable metals economic to mine
ore deposit - an accumulation of metals economic to mine
ore mineral - mineral that contains valuable metal
gangue mineral - low value waster mineral (quartz, calcite)

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4
Q

Copper

A
  • ore mineral - chalcopyrite
  • formula - CuFeS²
  • brassy
  • tetragonal
  • metallic
  • hardness - 3.5-4
  • streak - green-black
  • density - 4.2
  • cleavage - none
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5
Q

Gold

A
  • ore mineral - Gold
  • formula - Au
  • yellow
  • cubic
  • metallic
  • hardness - 3
  • streak - gold
  • density - 19.3
  • cleavage - none
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6
Q

Iron

A
  • ore mineral - Magnetite
  • formula - Fe³O⁴
  • black
  • cubic
  • metallic
  • hardness - 6
  • streak - black
  • density - 5.2
  • cleavage - poor
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7
Q

Lead

A
  • ore mineral - Galena
  • formula - PbS
  • grey
  • cubic
  • metallic
  • hardness - 2.5
  • streak - grey
  • density - 7.5
  • cleavage - 3 at 90°
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8
Q

Tin

A
  • ore mineral - Cassiterite
  • formula - SnO²
  • brown
  • tetragonal
  • adamantine
  • hardness - 6-7
  • streak - brown
  • density - 7
  • cleavage - poor
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9
Q

Zinc

A
  • ore mineral - Sphalerite
  • formula - ZnS
  • brown
  • cubic
  • adamantine
  • hardness - 3.5-4
  • streak - brown
  • density - 4.1
  • cleavage - 6 at 60°
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10
Q

Secondary enrichment of copper

A

Secondary enrichment concentrates ores - increases the grade

  • leaching - copper dissolves in solution and moves downwards
  • iron is insoluble and forms insoluble cap (gossan)
  • malachite and azurite (oxides) are precipitated in oxidising conditions above water table
  • chalcopyrite (sulphide) is precipitated in reducing conditions below water table

diagram 20

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11
Q

Formation of porphyry copper deposit

A

E.G Bingham canyon, Utah, USA
->15million tonnes of copper

  • porphyry deposit - forms from hydrothermal veins in a large granite intrusion in destructive plate margin
  • Water from subducted plate + metals + heat from vein
  • sulphides and silicates are immiscible, so copper minerals stay separate from magma
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12
Q

Exploration - geophysical techniques

A
  • used to measure physical properties of rocks

gravity survery
- uses gravimeteres to measure variations in GFS
- positive anomaly = dense metallic ore / mafic
- negative anomaly = low density silicic intrusion

magnetic survery
- uses magnetometer to measure variations in MFS
- minerals rich in iron produce positive anomalies

electromagnetic survey
- measures ground conductivity
- waves induce current in conducting materials / metal

electrical resistivity survey
- current passes between 2 electrodes
- low resistance = good conductor

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13
Q

Exploration - geochemical techniques

A
  • metals undergo dispersion by weathering, erosion and transport

stream sediment sampling
- samples downstream from source will have high metal conc
- sample each tributary to trace anomaly upstream to source

soil sampling
- samples downslope from source will have high metal conc
- used if no outcrop is visible

water sampling
- surface water (river) is tested in water survey
- if background conc is higher than a few ppb, a metal deposit is near

vegetation sampling
- plants uptake metal elements through roots
- high conc of element in leaves = underlying metal deposit
- high distribution of plants tolerant to high metal conc = underlying metal deposit

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14
Q

Mining - open cast

A
  • remove overburden
  • sediment / blasted ore is removed
    -dragline, hydraulic dredging
  • cheap, safer, fast
  • noise, dust environmental damage, visual pollution
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15
Q

Mining - Longwall retreat

A
  • work in blocks and roads (grid)
  • mechanised: cutter-shearer, conveyer-belt, hydraulic roof support
  • start away from access shaft
  • cut a longwall
  • cut towards the access shaft
  • allow roof to collapse behind

-cost effective (no ore left), mechanised (safe)
-expensive set up, roof collapse leads to subsidence

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16
Q

Mining - stope mining

A
  • used on steeply dipping hydrothermal veins
  • uses explosives and gravity

1 identify ore body
2 dig shaft
3 dig tunnel/road
4 explosives in roof
5 broken ore falls
6 when roof is too high, new tunnel is made higher up
7 explosives in roof, repeat

17
Q

Life cycle of a mine

A

1 design / planning

  • assesses if the project is economically viable, environmentally safe and socially responsible

2 construction

  • includes extraction, processing facilities, roads, etc

3 production

  • mining occurs via open cast or underground, depending on depth, shape and size of target body
  • depends on limits due to health and safety, technology, environment, etc

4 processing

  • materials are sent through crushers, separating valuable ore from waste rock
  • improves economic value of smelting

5 reclamation

  • Once a mine is exhausted, land needs to be returned to original state
  • ensure public health and safety, minimise environmental effect, remove hazardous material and waste, etc
18
Q

Placer deposits

A
  • deposits of cassiterite, gold and diamond (hard, little cleavage, insoluble)

Locations:
- confluence (rapid tributary
enters slow river)
- waterfall
- inside of meander
- beach

19
Q

Dredging and hydraulic mining

A

Advantages

  • easy access to loose sediment
  • cheap
  • ores are already concentrated
  • lower environment impact

Disadvantages

  • scars landscape
  • noise
  • dust
  • Water pollution
  • placers are used up quickly
20
Q

Fracking

A
  • well is drilled into shale
  • casing is inserted and surrounded by impermeable cement
  • charges are detonated to blast holes into the shale
  • pressurised fluid pumped into well
  • fluid generates small fractures, freeing trapped gas which flows to surface
21
Q

Mineral processing - in situ eaching

A
  • chemical solution dissolves ore from deep rock
  • drill borehole, frack, pump solution
  • pregnant solution pumped back up (contains dissolved ore)
  • e.g water for evaporites
  • e.g acids for copper
22
Q

Mineral processing - heap leaching

A
  • ore is crushed (large SA:V)
  • heap onto impermeable liner
  • solution percolates through, pregnant solution collects in pond

-cheap
-only recovers 60%
-slow

23
Q

Mineral processing - froth flotation

A
  • hydrophobic metal e.g sulfides
  • hydrophilic gangue e.g quartz
  • crushed ore added to water to make slurry
  • chemical added makes hydrophobic metals agitate with bubbles
  • froth contains metals, tailings left at bottom
  • tailings are toxic + contain chemicals, need to be stored correctly

Diagram 24

24
Q

Mineral processing - smelting

A
  • extracts metal using heat
  • releases co2 and sulfur dioxide
25
Q

Acid Mine Drainage

A
  • sulphides are mined
  • Water + oxygen + sulphides = sulfur Dioxide
  • sulfur Dioxide + water = sulfuric acid (AMD)
  • AMD dissolves toxic metals (lead, arsenic, mercury)
  • orange colour indicates iron oxide in water so there was a change in chemistry underground
26
Q

Managing AMD

A

Source control

  • stop AMD by stopping water or oxygen entering mine
  • e.g pumping a mine
  • e.g flood and seal with impermeable clay

Active treatment

  • add bases to AMD to neutralise acid and precipitate metals
  • e.g crushed limestone
    • expensive
    • high maintenance

Passive treatment

  • ideal for remote AMD
  • wetland ecosystem
  • natural oxidation precipitates metals
    • expensive to create
    • large space required
    • minimum maintenance

Geology A Level (8 decks)

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