Lecture 26

Question 1

Mineral Resources

Answer 1

Use almost all the naturally occurring chemical elements

More than 200 different minerals are mined

• metallic minerals for their constituent metals
• non metallic minerals for their chemical or physical properties

Question 2

Resource and reserve

Answer 2

Resource: naturally occurring accumulation of material in concentrations or amounts that make extraction currently or potentially feasible

Reserves: resources that can be exploited economically under present conditions

Question 3

Mineral and ore deposits

Answer 3

Mineral deposits: localized concentration of resource

Ore deposits: a mineral deposit that can be exploited economically

Question 4

Five parts of the rock cycle that produce mineral deposits

Answer 4

1. Magmatic concentration
2. Hydrothermal concentration
3. Weathering(residual) concentration
4. Physical sediment concentration (placers)
5. Chemical sedimentary concentration

Question 5

Magmatic mineral deposits: cumulates

Answer 5

• minerals crystallize from magma as it cools

- in intrusion, can get minerals settling to form layers

Question 6

Hydrothermal mineral deposits

Answer 6

• circulating groundwater is heated in many volcanic areas
• hot groundwater alters minerals, dissolves trace amount of metals such as Cu, Pb, Zn, etc
• as water returns towards surface it may either cool rapidly, boil (reduced pressure) or interact with oxygen
• any of these processes may reduce the solubility of dissolved metals, which will precipitate as mineral deposits

Question 7

Clastic sediments: placer deposits

Answer 7

• flowing water is effective at sorting sedimentary particles by size and weight
• dense minerals like gold or diamond may be concentrated in sands

Placer deposits:

• downstream from tributary
• inside meander loops
• behind undulations on ocean floor

Question 8

Non clastic sedimentary deposits: evaporites

Answer 8

• evaporites are rocks formed from evaporation of sea water (sometimes lake water)
• gypsum-plaster
• salt-roads, humans and animal feed
• potash-fertilizer

Question 9

Limestone and cement (non clastic)

Answer 9

• limestone are mined for buildings
• if limestone is heated with clay, other silicates and/or sulphites, cement is formed
• combined with sand and gravel to make concrete

Question 10

Impacts of mining: physical excavation of rock

Answer 10

• volume of removed material may be difficult to place

- increased erosion adds sediments to streams

Question 11

Impacts of mining: smelting

Answer 11

• extraction of metal from ore
• metal has to be removed from compounds with sulphur, oxygen, silicon
• sulphur oxide released during processing of many deposits

Question 12

Impacts of mining: tailing and acid mine drainage

Answer 12

-storage of removed rock that is not ore (tailing)

• may be reactive when exposed to oxygen and water
• most sulphides produce sulphuric acid
• pH of surface and ground water falls (detrimental to plant and animal life)

E.g. giant mine Yellowknife (arsenic)

Question 13

Categories of energy resources

Answer 13

Hydrocarbons:

• coal
• petroleum (oil, natural gas)

Nuclear fuels

Renewable energy resources:

• hydroelectric
• wind
• wave
• tide
• solar

Question 14

Coal

Answer 14

• comes from accumulated plant remains: peat
• peat undergoes coalification:
• during burial and heating organic polymers lose H and O by releasing H2O, CO2, and methane
• remaining coal is increasingly pure carbons:
  
  • lignite
  • sub-bituminous
  • bituminous coal
• if metamorphosed:
  
  • anthracite

Question 15

Coal seams

Answer 15

• because coal is sedimentary rock, it forms beds: coal seams
• thickness is mm to >10m
• 8m of peat forms 1m coal
• methane released during coalification may remain trapped in fractures within seam: coalbed methane (CBM)

Question 16

Organic rich shales

Answer 16

• organic matter is trapped in smaller concentrations in shales
• abundant where organic matter deposition was in low oxygen conditions
• black shale may have 8 percent or more organic matter
• solid organic matter in sediment is kerogen

Question 17

Maturation of kerogen

Answer 17

During burial and mild heating, kerogen gives off liquid and gaseous hydrocarbons

• bitumen and tar
• oil
• natural gas

Question 18

Petroleum migration

Answer 18

• oil and gas are less dense than water (which fills most pore spaces)
• will rise through permeable rocks
• may escape to surface in “seeps”
• may be trapped by structures where impermeable layers stop escape

Question 19

Unconventional hydrocarbons

Answer 19

• oil sands/tar sands

- hydraulic fracturing

Question 20

Nuclear fuels

Answer 20

• uranium is fuel
• concentrated by hydrothermal processes and also in sedimentary rocks
• uranium undergoes slow, natural radioactive decay releasing geothermal energy
• 235 U can be used to accelerate release of energy in a chain reaction
• 235 U undergoes radioactive decay by fission which splits the nucleus and releases neutrons and causes other atoms to undergo fission
• release large amounts of energy (heat to generate electricity, nuclear explosions)

Question 21

Local impacts of production

Answer 21

Coal mining:

• requires removal of large volume of rocks
• underground mining, surface “strip” mining
• coalbed methane release
• waste rock disposal

Petroleum production:

• accidental escape of oil and gas
• high sulphur “sour” gas is poisonous
• use of water

Question 22

Local impacts of production: sulphur

Answer 22

• many fossil fuels contain sulphur
• released as SO2 during combustion
• contributes to acid rain

Question 23

General impacts of fossil fuels

Answer 23

Greenhouse gas emissions:

• burning of fossil fuels releases CO2
• fossil fuels containing H produce some of their energy by making H-O bonds: produce less CO2 per joule of energy
• natural gas is mostly methane
• oil has more C less H
• coal is mostly C