Geopix UK - Other Titles

Natural Resources

COAL

Coal develops - over millions of years - by the partial decomposition of thick layers of peat derived from luxuriant vegetation which grew, typically, on the flat, low-lying land of a delta, in a humid equatorial climate. Unless subsequently subjected to earth movements, the coal seams are now horizontal, with other rock above and below.

What is the best way to extract a horizontal, one-metre thick layer of coal cheaply;

without removing any of the unwanted rock above and below;

without roof falls and other collapse;

without the risk of explosion and fire;

without causing subsidence at the surface?

Which is better - deep mining or opencast (open-pit) mining/quarrying?

In Britain, there is a lot of coal which has not yet been mined.
What are the geological reasons for not exploiting a coal seam, in terms of

coal quality;
depth;
nature of the seam;
geological structure?

PETROLEUM

Oil and gas - another variety of fossil fuel - developed from the partial decomposition of minute, marine, planktonic animals. What conditions are needed to prevent the dead organisms from being swept away when they sink to the sea floor, and to prevent the organic material from decaying away altogether? What conditions forces all of the minute drops of oil into the same reservoir rock without it escaping to the surface?
A typical oil and gas trap is the anticline, with an arched reservoir rock - porous and permeable - overlain by an impermeable cap rock. These structures are deep underground and may be hidden by completely different rocks on top. They must be located by remote sensing - seismic surveys, gravity surveys, magnetic surveys and so on.

Once the anticline is detected, the only way to test for the presence of petroleum is to drill. The chances of finding an economical reservoir of oil is no higher than 10% - exploration for oil is an expensive business.

With the reserves of conventional petroleum being used up, attention is turning to unconventional sources, such as tar sands. What are the problems of strip-mining vast amounts of oily sand from the Earth's surface and turning it into usable hydrocarbons?

EVAPORITE DEPOSITS

Rock salt (halite) and gypsum are deep-mined in a similar way to coal - though in rather better conditions. Halite is also extracted from underground seams by solution mining - pumping water down and drawing the brine up. How should pumping be controlled to avoid the subsidence which at one time caused so much damage in parts of Cheshire?
What can you do with a worked-out rock salt mine?

METAL ORES

Metal ores have a range of origins and therefore a range of mining methods. Hydrothermal veins often follow fractures within the host rock and can be worked as high grade ores by following the often random course of the vein or lode. As with all deep mining, there is the chance of rock falls and collapse. What types of good engineering practice can be used to prevent falls?

In other cases, the ore is spread thinly throughout the host rock. To get this low grade ore, the whole of the rock must be extracted, crushed and treated. The result is huge holes in the ground and huge amounts of waste rock - perhaps 100 tonnes of rock for each tonne of useful ore. Open-pit mines bring their own safety issues, involving potential rock falls and pollution of surface waters, quite apart from environmental issues of dust, noise and vibration. What steps should be taken to prevent these hazards?

When the mine is abandoned, the chemical (sulfide) ores still in the ground react with oxygen and water now in free supply within the mine, leading to the formation of acids, which dissolve other chemicals and heavy metals. These solutions may contaminate the local groundwater. Waste tips contain heavy metals which prevent re-vegetation of the scarred landscape.
The photograph shows the former copper mine at Parys Mine, Anglesey.

BULK RESOURCES

Hundreds of millions of tonnes of sand, gravel, roadstone, limestone and other building stone are quarried each year. These bulk resources are widely available and are of low economic value. The large quantities involved means that the source should be as close as possible to the market to keep transport costs down. However, it is not quite so simple:

there are different kinds of sand; a river sand and a beach sand have different textures;
there are different kinds of limestone: chalk is better for making cement than is Carboniferous Limestone, and Jurassic Limestone is a better building stone than chalk;
the rock used for roadstone has to bind with the bitumen, provide grip for tyres, wear well but not get polished;
some clays are used for making bricks, others for making glossy paper and porcelain.

Once again, quarrying leaves holes in the ground. What should happen to them?

The photograph shows a china clay in Cornwall.

Geopix Study Topic "Natural Resources"

Coal: formation, methods of mining, hazards of mining, difficulties for modern mining.
Petroleum: formation, accumulation, exploration, extraction; unconventional sources.
Evaporite deposits: formation, methods of extraction, prevention of surface subsidence.
Metal ores: hydrothermal veins, methods of extraction, acid mine drainage.
Uranium ore.
A glossary of mining terms.
A summary of bulk resources.

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