Coal mining

Coal mining

The goal of coal mining is to obtain coal from the ground. Coal is valued for its energy content, and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United States,...

 cannot be done everywhere with coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, due to certain geological restrictions.

Faulting

If the coal seam reaches a fault, the seam may be significantly displaced, depending on the type of fault and its offset. Machinery trying to mine the coal may not be able to reach the displaced seam, if the displacement is too large. Coal mines use a combination of boreholes and high-resolution seismic reflection data

Reflection seismology

Reflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...

 to identify the larger faults and avoid the most faulted areas at the mine planning stage.

Water table

If the water table

Water table

The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...

 is too high, the mine will flood with water. While mining, water needs to be constantly pumped out and this is expensive.

Washout

If a distributary

Distributary

A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel. They are a common feature of river deltas. The phenomenon is known as river bifurcation. The opposite of a distributary is a tributary...

 or river changes course and cuts into the swamp material that will form coal, the coal seam is not fully formed and there may be a problem with mining it.

Thickness of seams

If the seams are too thin it may be uneconomical to mine the coal. The cost of production could exceed the selling price.

Splitting of seams

If the seam splits, due to a delta

River delta

A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...

 collapsing, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

 and silt

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

 sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s pile up on top until that area is covered. This may make all or part of the coal seam uneconomical to mine as it is too thin.