Wyoming holds more than one-third of the nation’s mineable supply of coal. It produces more coal than Texas, West Virginia, Kentucky, Pennsylvania, Illinois and Montana combined. The state’s 18 active mines employ about 6,500 people.
Wyoming’s Powder River Basin coal is easier to access than most other U.S. coal, and it burns cleaner.
But for the details — answering how the coal formed, just how much is there and how long it will last — the Star-Tribune presents Powder River Basin Coal 101 with information from the U.S. Geological Survey, Chris Carroll, a coal geologist with the Wyoming State Geological Survey, and James Luppens, project chief for the U.S. Coal Assessment Program for the USGS.
How did PRB coal form?
Wyoming’s Powder River Basin coal formed roughly between
130 million and 50 million years ago, during what geologists call the Cretaceous and early Tertiary periods. Most of the coal currently mined formed during the Paleocene Age, between 65 million and 55 million years ago, when the state’s high desert plains were covered by lush swamp and tropical forests.
As plants and trees died, they formed peat, which, as it became compressed over millions of years, became coal. Some deposits still have tree trunks and leaf patterns fossilized from the original swamps. Depending on where mountains and basins subsided between tectonic uplift areas, the swamp would rise, fall and move, creating thicker deposits in some places and thinner ones in others. Much of the coal is relatively close to the surface, making it easier to access than all of the country’s other coal deposits.
Why is it considered cleaner than other coal?
The term “clean” refers to the Powder River Basin coal’s sulfur count. It has about 0.3 percent sulfur when it is taken from the ground, compared with more than 1.2 percent sulfur in most of the coal in the Illinois Basin, for example. Brackish water, or fresh water mixed with salt water, causes higher sulfur. Because much of the coal in the Powder River Basin came from a freshwater swamp, the salt contamination was limited.
How much is there?
The amount of coal in the Powder River Basin is much less important than the amount of mineable coal. And the amount of mineable coal depends on where it is, how deep it sits and how good the technology is to mine it. Coal, for example, near the towns of Gillette and Wright, will likely never be mined.
In the 1990s, for example, coal companies could economically mine coal if the ratio of ground on the top was no more than
2-to-1. That meant for every 2 feet of rock and soil, miners collected 1 foot of coal. Now, companies are mining as much as
3-to-1, or even greater. Wyoming’s amount of economically recoverable coal could change if companies can afford to go deeper. Underground mining is also not used in the Powder River Basin in Wyoming, but one day it may be economically feasible to try.
The USGS estimates the Wyoming portion of the Powder River Basin has about
855 billion tons of in-place coal resource, with 768 billion tons that are available, which means it’s not under a town or other land use restriction. Of that amount, 127 billion tons is recoverable, which means it can be removed. Ultimately, 11.6 billion tons is economically recoverable reserves at today’s prices. At any price and a rate of 400 million tons of coal per year, the Powder River Basin would last another 317.5 years.