Iron ores

Question 1

Iron occurs as:

Answer 1

• Ferric iron can oxidise organic matter and reduce to ferrous iron
• ferrous iron can be re-oxidised by atmospheric oxygen

Question 2

Fe2O3

Answer 2

Ferric iron

- has low solubility in water

Question 3

FeO

Answer 3

Ferrous iron

- has high solubility

Question 4

Iron

Answer 4

• helps transfer oxygen from air or water to body tissue
• also occurs in chlorophyll
• some bacteria have an enzyme that transfers electrons from FeO to O2 as an energy source
• deposits are formed by many different processes

Question 5

key iron ore minerals

Answer 5

• Haematite
• Magnetite
• Limonite
• Siderite

Question 6

Iron deposits

Answer 6

• magmatic deposits e.g. cumulates
• weathering (oxidation to ferric iron & laterite soils)
• banded iron formations

Question 7

Banded Iron Formations

Answer 7

• alteration between ferric iron and chert rich layers
• small uniform grains
• large deposits
• range between 2.5 billion to 1.8 billion years old

Question 8

Banded Iron Formation process

Answer 8

• combing the Fe and O2 ions (from blue/green algae) into magnetite
• mineral grains sink to the sea floor
• accumulate into iron rich and iron poor layer

Question 9

Iron Production

Answer 9

• 98% of iron ore (mostly haematite and magnetite) used in steel making
• mined in approx 50 counties
• Australia and Brazil each have around 1/3 of total exports

Question 10

Residual Deposits (Laterites & Bauxite)

Answer 10

• deep tropical weathering
• peak from 35-1.5 million years ago (warm humid climate)
• leaching of parent material
• low topography

Question 11

Leaching of parent material

Answer 11

• removes soluble components - acid leaching of parent minerals
• hydrolysis and precipitation of insoluble ions (Fe and Al)
• wet season: Leaching by percolating rain water
• dry season: Leached ions brought to surface by capillary action from salts
• next wet season: Soluble salts washed away

Question 12

Bauxite

Answer 12

• no unique composition
  * Gibbsite - common
  * Typically 20-30% ferric iron
• Aluminium comprises 7% of the crustn
• Large blanket deposits in W.Africa, Australia, S.America and India
• global production approx 56.8 million tons per year
• most production of aluminium in China
• recycling in UK = 55%

Question 13

Witwatersrand Gold Deposits

Answer 13

• Archean in age
• approx 3000 million years ago, sediment, including BIFs and tillites, deposited in a shallow sea ‘West Rand Group’
• 60 million years later, sediments deposited on coastal plain and wide braided rivers
• ‘Central Rand Group’ contains gold, uraninite, pyrite
• worlds largest known gold reserves (40%)
• produces 1.5billion ounces of gold
• also a critical source of uranium

Question 14

Residual deposit

Answer 14

• a deposit formed by the alteration of a pre-existing rock of which large part of its constituents have been lost by dissolution and which has therefore become enriched in certain minerals or elements.