4.5 Global distribution of coal

Figure 35 shows the global distribution of coal deposits. The major areas are principally in the Northern Hemisphere; with the exception of Australia, the southern continents are relatively deficient in coal deposits.

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4.4 Coal in the European Union

The EU's coal reserves in 2004, after enlargement to 25 member states, stood at 100 × 109 t. Table 3 shows the eight European Union Member States with the most significant reserves ranked in order of greatest tonnage. With a little over 100 × 10 9 t of coal of all ranks, the EU possesses approxima
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4.3 The UK's coal reserves

Production of large quantities of coal in the UK during the 19th and 20th centuries led to the progressive depletion of reserves. In 2005 underground mining was limited to the Carboniferous coalfields of Yorkshire and the East Midlands, with only one underground mine operating in South Wales. However, surface mining sites still work coal in most of the coalfields (Author(s): The Open University

4.2 Coal distribution in the UK and Europe

The UK and Europe were fortunate in having extensive coalfields that powered the Industrial Revolution. Figure 33 shows the distribution of the major Carboniferous mires which became coal-bearing rocks across Europe, either outcropping at the surface or buried beneath younger rocks. The first thing that is evident from t
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3.3.1 Mining subsidence

Subsidence is an inevitable hazard wherever underground mining is carried out.

The major factors affecting the extent of subsidence are seam thickness and its depth beneath the surface.

The amount of subsidence can be calculated roughly by using the formula:

3.3 Underground mining

Underground mining operations have four significant environmental impacts — spoil heaps, methane build-up, subsidence and water pollution. Spoil heaps have always been the principal surface feature of underground mining operations. However, legislation and technical advances have brought improvements in modern mines, and the closure of many of the UK's older mines has often been followed by successful rehabilitation of mine sites and spoil heaps by landscaping and tree planting.

Coal
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3.2 Surface mining

Many environmental issues arise when surface mining is considered, and such mines regularly arouse local opposition. By their very nature, surface mines have a major impact on the landscape, involving the digging of enormous pits with accompanying noise, dust and traffic movements, and destruction of mature landscape. Increasingly, in recent years the environmentally conscious public has used the planning processes to oppose and sometimes prevent mining on sites where the environmental impact
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3.1 Environmental aspects of coal mining

Coal produced by both types of mining is used either to fuel electricity generation or for industrial and domestic heating, both of which result in atmospheric pollution, but here we are concerned with direct environmental impact on the land. Surface and underground mining operations cause significantly different environmental problems. Those that surround surface mining are common to any large quarrying operation: sterilization of the land and restoration of quarry sites; dust; and noise whi
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2.7.1 Recognizing geological problems

The most profitable coal mines are those that possess unbroken, horizontal seams of constant thickness and quality. In mines where this is not so, profit levels will depend on the ability of the mine geologist to predict changes in the seam before they are encountered at the face.

Geological problems fall into two categories — gradual changes and sudden changes. Where a change is gradual, such as a seam thinning or splitting, data from boreholes in advance of the workings, supplemente
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2.7 Geological problems in coal mines

A modern coalface is a very complex operation that represents a large investment in terms of capital, labour and planning. Cutting machines and lengthy conveyors are inflexible and require uniform geological conditions to maximize output. What then are the effects of geological variations on such a mining system?

Geological factors control the selection of working areas. The two principal geological conditions that affect mining operations are, first, the nature of the coal-bearing rock
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2.6 Underground mining

Coal extraction is of course less straightforward using underground mining techniques. The associated costs are higher, and these begin with the sinking of two shafts, an ‘upcast’ and a ‘downcast’ shaft for ventilation (Figure 22). Sinking these to a depth of a kilometre may take a few years and during thi
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2.4 Modern mine planning

Once the geological data gathered during the exploration phase has been evaluated, geologists will estimate the quality and quantity of coal present. Coal reserves (in tonnes) are calculated from volume × density (Section 5). The volume of coal is controlled by seam area and seam thickness.

Hence:

tonnage = se
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2.3.4 Geophysical methods — borehole logging

If a core is not recovered from a borehole, another way to assess the types of rock that it penetrates is to measure their physical properties. Mounting a string of electronic instruments behind the drill bit most conveniently does this: it allows the properties of the rock to be monitored as the borehole is drilled. An alternative is to lower instruments down the completed borehole by cable; hence the name wireline logging.

Such logging measures several physical properties of th
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2.3.3 Drilling

Drilling is expensive, so this next phase of exploration only begins when all the data have been gathered from pre-existing geological and topographic maps, aerial/satellite photographs, geological mapping and from seismic surveying.

The thickness and quality of a coal seam in an area are first determined by drilling boreholes a few kilometres apart using a grid pattern. Mobile drilling rigs (Author(s): The Open University

2.3.2 Geophysical methods — seismic surveying

Geophysical survey methods use measurements made at or near the Earth's surface to investigate the subsurface geology. The most widely used geophysical method is seismic reflection surveying; a rapid and highly cost-effective way of gathering data.

A seismic source (produced either by the explosive release of compressed air in a shallow borehole, or a heavy pad vibrated hydraulically at the surface) generates seismic waves that travel through the ground (
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2.3.1 Geological mapping of coalfields

Coalfields can be divided into two categories: exposed coalfields, where the coal-bearing strata outcrop at the surface, and concealed coalfields, where they are hidden beneath younger rocks. Exposed coalfields can be defined with considerable precision by surface geological investigations; indeed geologists recording field data still represent the cheapest exploration ‘tool’ available to the coal industry.

In populated regions, the locations of coal outcrops are well
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2.3 Exploring for coal

Early miners would have found it easy to trace the distinctive black colour of coal along an outcrop (for example, a coastline or river valley), and surface trenches were used to locate less obvious outcrops. However, tracing an outcrop underground was problematical as the only means of exploration was by digging costly trial shafts. The development of exploratory steam-powered drilling in the early 19th century improved matters, but it was not until the mid- to late- 20th century that more a
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2.2 Winning coal in former times

Coal was probably first used as a fuel by early Chinese civilizations, and there is evidence for coal working in the UK since Roman times. However, early approaches to mining were limited by the available technology, and left much of the coal behind.

At first, coal was dug from seams exposed at the surface in shallow excavations into valley sides that followed the coal seam. The amount of coal that could be extracted from these trenches and from adits (short horizontal tunnels) w
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2.1 Finding and extracting coal

Coal is often regarded as the principal fossil fuel, and with good reason. There is almost three times more energy available from the global proven coal reserves as there is from proven oil and gas reserves taken together. Therefore, it is unsurprising that even today much time and effort is spent locating it.

This section considers the techniques used in coal exploration and how coal is produced from surface and underground mines. But first, a brief look at a few of the historical aspe
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1.7.1 Carboniferous mires

During the late Carboniferous, mires developed over vast areas of the UK. Much of today's land area was an extensive, low-lying plain bordering a sea to the south (a sea that was soon to be the site of a mountain-building episode). Any mountains that existed lay hundreds of kilometres to the north. Large river systems meandered southwards across these plains.

At that time, the UK lay in tropical latitudes, almost on the Equator (see Author(s): The Open University