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.

Reach Assistant Content Director Christine Peterson at 307-746-3121 or christine.peterson@trib.com. Follow her on Twitter @PetersonOutside.



(2) comments


There are more mineable reserves of the very same Powder River basin coal seams in montana than Wyoming. it's just that Wyoming pimped out its coal while Montana rewrote its constitution to add environmental safeguards back in 1972, besides insisting on a much higher state severance tax. Wyoming needs that same 15 percent severance tax more than ever these days, while we can still get it...

Leslie Glustrom
Leslie Glustrom

Thanks for the background on Powder River Basin coal.

Last sentence is key--it says "at any price" Wyoming coal could last over 317 years--this is referring to technically recoverable coal (as long as we don't care how much it costs.)

All the external costs of coal aside (e.g. mercury, particulates, carbon dioxide and climate change etc.), we certainly do care how much we pay for coal (especially as renewable energy costs fall.)

Using the USGS number of 11.6 billion tons of economically recoverable coal and production of 400 million tons, Powder River Basin coal would only last about 29 years--a very different answer than the 317 years given by the article.

The truth is, there are many signs that we are rapidly approaching the end of economically recoverable coal in the US and in the Powder River Basin. The top 4 US coal companies are running in the red and increasingly the more coal they mine, the more money they lose because it costs them more to mine the coal than they can sell it for. Production in the Wyoming PRB was below 400 million tons last year and likely to keep trending generally downward from the apparent peak in 2008 of 467.6 million tons.

Lots more information available by searching "Warning: Faulty Reporting of US Coal Reserves" or by contacting the author.

Leslie Glustrom
lglustrom at gmail.com

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