Powder River Basin Coal Field
In the Powder River Basin coal field – the most prolific in the world – coal is mined from two major coal seams, the Anderson and Canyon coals. This coal occurs in the Paleocene-age (65 to 55 million years ago) Tongue River Member of the Fort Union Formation. The mineable subbituminous coal seams in the Fort Union Formation are 60 to 80 feet thick, with a moisture content between 20 and 30 percent, and contain less than 6 percent ash and 0.5 percent sulfur. Powder River Basin (PRB) coal also extends into the Eocene-age Wasatch Formation, and exploration drilling has encountered coal seams greater than 200 feet thick.
Coal is mined in the PRB at a rate of 12 tons per second, filling between 50 to 70 coal trains per day. Nine of the nation’s 10 largest coal mines operate in the Wyoming part of the PRB. The largest coal mine is the Peabody Energy North Antelope Rochelle Complex, which produced more than 107.6 million tons in 2012.
The PRB also has over 1,500 square miles of clinker rock. This is a layer of reddish rock formed by baking of sediments above burned coal deposits. Historically coal deposits exposed at the surface were ignited by lightening strikes or brush fires and burned naturally underground and near the surface for a period of hundreds of years. Recent age-dating suggests that these beds are between 1.1 Ma to 10 ka in age (Heffern et al, 2007). These clinker beds are up to 180 feet thick.
The southern portion of the Powder River Basin
is located in northeast Wyoming.
Rapid growth in Wyoming's coal industry during the latter part of the 1970s resulted from the development of large-scale open-pit surface mines in the Powder River Basin (PRB). Development of the abundant coal resources in the PRB was driven by amendments to the Clean Air Act of 1974 and the following energy crisis. The continuous growth of coal production in Wyoming resulted from a growing national demand for low-cost, low-sulfer steam-coal; from technological advances in engineering and mining practice; from large-scale development of mining and rail infrastructure; and from the great abundance of thick, mineable coal resources in the PRB.
Mining in the PRB
(Click photo to enlarge)
PRB Coal Correlations and Coal Zones
Well logs are displayed in these cross section diagrams indicating the locations, names and thicknesses of coal seams in the PRB. Coal Correlations and Coal Zones in the Powder River Basin, Wyoming Cross sections A-A’ through F-F’, can be viewed online or purchased through the WSGS online store. WSGS-2007-OFR 2007-03.
-Clinker Distribution & Age in the Powder River Structural Basin (2007 Geologic map by Ed Heffern showing clinker locations in the PRB.)