Black Thunder Coal Mine, WY, USA

The Black Thunder thermal coal mine, located in the Southern Powder River Basin of Wyoming, opened in 1977 and for many years was the largest single coal operation in the US. Having been relegated to second-largest, after Peabody's North Antelope-Rochelle operation, also in the Powder River Basin, in 2004 Black Thunder once again became the nation's leading coal-producer following Arch Coal's acquisition of the neighbouring North Rochelle mine from Triton Coal Co. The combined operation is now producing coal at a rate of around 91Mt/y, equivalent to about 10% of total US coal production. In 2004, Black Thunder became the first coal mine in the US to ship a cumulative 1,000Mst (907Mt) over its 27-year life to date.
Construction began at Black Thunder in 1976 with the installation of crushing, conveying, sampling and high-speed train-loading systems. Today, all plant processes are computer controlled, including the precision loadout systems and the hi-tech, near-pit crushing and conveying system installed in 1989.
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Until 1998, Black Thunder was owned and operated by ARCO Coal, part of the Atlantic Richfield group. It is now owned by Arch Coal, the second-largest coal miner in the US, which bought the property following ARCO's withdrawal from the coal market.
GEOLOGY AND RESERVES
Black Thunder works coal reserves in the Wyodak seam. Hosted in the palaeocene Fort Union formation, which covers vast areas of Wyoming, Montana and the Dakotas, the seam at Black Thunder is gently dipping, 22m thick and locally splits into the Anderson and Canyon beds separated by up to 18m of waste. In 2004, Arch successfully bid $611m for the rights to mine the neighbouring Little Thunder reserves, which contain some 650Mt of recoverable coal, increasing the property’s reserves to 1,370Mt-plus.
COAL QUALITY
The mine produces low-sulphur, sub-bituminous coal suitable for power station fuel without any preparation except crushing. Black Thunder coal has a heating value of 20.3MJ/kg, and the ash contents are around 5% while as-received moisture is 25–30%. The moisture content of some Powder River Basin coals increases their reactivity to the extent that spontaneous combustion can be a problem if they are not properly handled.