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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 world. It is also the first coal mine in the world to transport one billion tons of coal.
Having in 2004 been relegated to second-largest, after Peabody’s North Antelope-Rochelle operation, also in the Powder River Basin, 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.
In October 2009, Arch purchased Jacobs Ranch mine from Rio Tinto and merged it with its Black Thunder mine to become the world’s largest coal mining complex.
The combined operation supplies over 10% of the 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. Since its opening, the mine has produced and delivered around 2.2 billion tons of coal.
Construction began at Black Thunder in 1976 with the installation of crushing, conveying, sampling and high-speed train-loading systems. All plant processes are computer-controlled, including the precision loadout systems and the hi-tech, near-pit crushing and conveying system installed in 1989.
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.
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.
Mining and shipment
Black Thunder operates several individual open pits within its enlarged concession area, using five large draglines for overburden handling. The dragline fleet includes Ursa Major, the largest of the three, a Bucyrus-Erie (B-E) 2570WS model weighing some 6,700t. The third-largest dragline ever built, it was assembled on-site over a three-year period at a cost of $50m.
Its 110m-long boom carries a 122m³ bucket. Of the other draglines, Thor, a B-E 1570W, has a 97.5m boom and a 69m³ bucket, while Walking Stick is a B-E 1300W with a 92m boom and a 34m³ bucket. Originally built at Coal Creek, another Arch Coal property where production was halted in 2000, it was tramped across the prairie to Black Thunder late 1991.
Arch resumed production at Coal Creek in the second quarter of 2006 in response to increased market demand. A dragline that had been moved from one of the company’s other operations in the Western US was also reassembled.
Around 15-75m of overburden had to be stripped after the topsoil was stored for use during restoration. Black Thunder relies heavily on cast blasting to move between 20 and 30% of the overburden to its final position directly. The remainder is handled by the draglines. The coal is also blasted before loading.
The coaling fleet consists of five P&H 2800 electric mining shovels and one Marion 351-M. Coal haulage is carried out by a fleet of Liebherr T-262 (218t-capacity) and Komatsu 930E (290t) haul trucks, and the mine has had both Liebherr T-282 (360t-capacity) and TI-272 (290t) trucks under evaluation.
Coal is hauled to a near-pit dump and crusher station, which feeds a 3.5km-long overland conveyor to the coal storage and loadout silos.
Black Thunder’s two 12,700t silos and 82,000t slot storage system feed twin rail load-outs with capacities of 4,100t/h and 10,800t/h. Both the Burlington Northern and Union Pacific rail systems service the operation.
At the beginning of 2006, Arch Coal and Peabody Energy undertook a swap of reserve and infrastructure assets that enabled both companies to optimise their future operations. In Arch’s case, this resulted in the sale of a rail spur and loadout facility, with the company using the proceeds to build a new rail spur and loadout close to its Little Thunder Creek reserves, where future operations will be focused.
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