Lecture 26 Flashcards
Mineral Resources
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
Resource and reserve
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
Mineral and ore deposits
Mineral deposits: localized concentration of resource
Ore deposits: a mineral deposit that can be exploited economically
Five parts of the rock cycle that produce mineral deposits
- Magmatic concentration
- Hydrothermal concentration
- Weathering(residual) concentration
- Physical sediment concentration (placers)
- Chemical sedimentary concentration
Magmatic mineral deposits: cumulates
- minerals crystallize from magma as it cools
- in intrusion, can get minerals settling to form layers
Hydrothermal mineral deposits
- 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
Clastic sediments: placer deposits
- 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
Non clastic sedimentary deposits: evaporites
- evaporites are rocks formed from evaporation of sea water (sometimes lake water)
- gypsum-plaster
- salt-roads, humans and animal feed
- potash-fertilizer
Limestone and cement (non clastic)
- 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
Impacts of mining: physical excavation of rock
- volume of removed material may be difficult to place
- increased erosion adds sediments to streams
Impacts of mining: smelting
- extraction of metal from ore
- metal has to be removed from compounds with sulphur, oxygen, silicon
- sulphur oxide released during processing of many deposits
Impacts of mining: tailing and acid mine drainage
-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)
Categories of energy resources
Hydrocarbons:
- coal
- petroleum (oil, natural gas)
Nuclear fuels
Renewable energy resources:
- hydroelectric
- wind
- wave
- tide
- solar
Coal
- 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
Coal seams
- 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)
Organic rich shales
- 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
Maturation of kerogen
During burial and mild heating, kerogen gives off liquid and gaseous hydrocarbons
- bitumen and tar
- oil
- natural gas
Petroleum migration
- 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
Unconventional hydrocarbons
- oil sands/tar sands
- hydraulic fracturing
Nuclear fuels
- 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)
Local impacts of production
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
Local impacts of production: sulphur
- many fossil fuels contain sulphur
- released as SO2 during combustion
- contributes to acid rain
General impacts of fossil fuels
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
