Illinois Basin Coal
The Illinois Coal Basin covers 65% of Illinois and portions of southwestern Indiana and western Kentucky.
Coal formation began during the Carboniferous Period, which spanned 360 million to 290 million years ago. Plant material was subjected to high temperatures and pressure as silt and sediment buried swamps and peat bogs. This caused physical and chemical changes in the vegetation, transforming it into coal. The degree of organic maturity determines the type of coal found.
Types of Coal
The least mature coal is lignite -- also called brown coal or soft coal. Lignite is a low-rank coal, lower in carbon and heat output. The continuing effect of temperature and pressure transformed lignite into bituminous coal -- also called hard coal or black coal. Continued organic maturity produced anthracite coal. Bituminous and anthracite are high-rank coals that are high in heat value because they are also high in carbon.
There are two categories of bituminous coal -- thermal and metallurgical. Thermal coal is used in electric power generation, cement plants and other industrial uses. Metallurgical coal is used the manufacture of iron and steel. Illinois coal is bituminous thermal coal.
According to the Illinois State Geological Survey Illinois' has the largest known bituminous coal reserves in the country. Of the 200 billion tons of coal estimated to lie underground in the state, the ISGS estimates about 38 billion tons of that coal can be mined economically.
Brief History of Coal Mining in Illinois
Observations by early explorers of coal outcrops along the Illinois River took place in 1668, 1669 and 1673. Coal mines in the early 1800s consisted of outcroppings of coal seams along the bluffs of rivers and streams. By some accounts the first commercial coal mining took place in 1810 along the banks of the Big Muddy River near Murphysboro in Jackson County. Underground coal seams were discovered when settlers began moving inland, away from streams and rivers, and began drilling for water. Coal mining grew into a major industry with the growth of railroads and increased manufacturing. Shaft mining was begun shortly after the completion of the Illinois Central Railroad in 1855 and within ten years the coal fields across the state were developed.
In 1882 the first yearly report to the State of Illinois documented 43 counties producing coal from 685 mines employing 20,299 miners, of whom 870 were under sixteen years old. Early underground, slope or shaft mines, were dug by hand with picks and shovels. Lumber was used to prop up the roof where the miners worked, but falling rock often trapped, injured or killed the them. Working in cramped conditions for ten or more hours a day, miners loaded coal onto small cars and pushed the cars to an area where mules would either haul the cars up the slope, or into a cage where the cars would be hauled up a shaft.
The Illinois Labor History Society describes the working conditions in early Illinois mines. "Miners breathed stale dusty air and many developed a breathing ailment known today as Black Lung. Miners complained that the coal companies did not supply them with adequate rails, cars, lumber, or fresh air. Explosive gas was present in some mines and many miners were injured or killed by blasts. In February, 1883, seventy-four miners were killed in the "Diamond Mine Disaster," when water from melting snow on the surface suddenly poured into the mine, drowning the men working below. It was the worst mining disaster in Illinois history up to that time."
Modern Coal Mining Methods
Illinois employs three basic types of coal mining: room and pillar, longwall, and surface or strip mining. The first two are forms of underground mining, while the third, as the name implies is done from the surface. Illinois produced approximately 52 million tons of coal in 2013. As of November 2014 there were 13 actively operating underground mines and 9 surface mines in Illinois.
The majority of coal produced in Illinois comes from from coal seams that lie 200 feet or deeper below the surface. Rooms 20 to 30 wide are cut into the coal bed leaving a series of 100-foot-wide pillars, or columns of coal, to help support the mine roof. As mining advances, a grid-like pattern of rooms and pillars is formed. Room and pillar mining generally recovers less that 50% to 60% of the coal.
The oldest form of room and pillar mining--conventional mining--uses a 4-step process where the coal seam is cut, drilled, blasted and then loaded into cars. The more prevalent form of underground mining today is continuous mining. With continuous mining a machine cuts the coal from the seam and loads it to a conveyance out of the mine. This technology elimantes the 4-step process while producing 4 to fifteen tons of coal per minute--more than a non-mechanised mine of the 1920s would produce in an entire day.
High-extraction Retreat Mining
Retreat mining was common in Illinois from the 1040s to 2002. It employs conventional room and pillar mining, but when the end of a panel was reached as much coal as possible is then mined from the remaining pillars. Removal of the pillars that were supporting the roof causes subsidence to the surface above. Sometimes pillars were left unmined to avoid subsidence and damage to structures on the surface. Up to 80% to 90% of the coal is mined, but roof collapse resulting from the removal of pillars also caused much more danger to the miners.
In longwall mining, coal is removed by a cutting machine that works back and forth across the coal face, cutting off coal as thick as the coal seam (5 to 9 feet) in panels approximately 1,500 feet wide and up to 3 to 5 miles long. As the coal is sheared off it falls onto a conveyor and is transported out of the mine. A steel canopy supports the weight of the roof and moves forward with each pass of the cutting machine. As the machinery advances forward the roof behind collapses in what is referred to as "planned subsidence."
The panels are separated by sections of room and pillar mining that allow access to the mine for workers, equipment and coal conveyers. Each longwall mine has numous, parallel panels that form the "shadow area" of the mine, which is usually 5,000 to 10,000 acres in size. The amount of subsidence on the surface above a longwall panel is usually 4 to 6 feet, or about 60% to 70% of the height of the mined out area. The resulting subsidence causes damage to structures, water wells, roads and bridges, and surface and underground drainage.
Longwall mining, which extracts approximately 90% of the coal, was the method used to mine rougly 40 percent of the coal mined in Illinois in 2013.
See Planned Coal Mine Subsidence in Illinois: A Public Information Booklet, published by the Illinois Department of Transportation and the Illinois State Geological Survey for detailed information about coal mine subsidense.