Evaluation of Economically Extractable Coal 

Resources in the Gillette Coal Field, 

Powder River Basin, Wyoming 

By Margaret S. Ellis1,Carol L. Molnia1, Lee M. Osmonson1, Allan M. Ochs2, 

Timothy J. Rohrbacher1, Tracey Mercier2, and Laura N.R. Roberts1

U.S. Geological Survey Open-File Report 02-180 

2002 

U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

1 U.S. Geological Survey, Denver, CO 

2 Consultant 

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial

standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not

imply endorsement by the U. S. Geological Survey. 
Contents 

Abstract ..........................................................................................................................................................4 

Acknowledgments.........................................................................................................................................4 

Introduction and Objectives..........................................................................................................................5 

Previous Coal Resource Calculations in the Gillette Area ..........................................................................5 

Definitions for this Study ..............................................................................................................................8 

Geologic Setting and Study Area..................................................................................................................9 

Coal Mining .................................................................................................................................................10 

Other Energy Commodities of the Area.....................................................................................................13 

Coal Bed Geology

Coal Bed Nomenclature.............................................................................................................14 

Coal Bed Correlations................................................................................................................15 

Coal Geochemistry ......................................................................................................................................26 

Factors Affecting Extraction of Coal Resources........................................................................................30 

Study Methodology

Data Collection, Correlation, and Preparation..........................................................................36 

Coal Resource Calculation.........................................................................................................37 

Results..........................................................................................................................................................41 

Conclusions..................................................................................................................................................43 

References Cited..........................................................................................................................................44

Figures

Figure 1. Generalized geologic map of the Powder River Basin showing the axis of the basin and 

the location and extent of the Gillette coal field ..................................................................6 

Figure 2. Generalized stratigraphic column for the Powder River Basin, Wyoming and Montana.........9 

Figure 3. Geologic map showing Tertiary and younger rocks, major roads, and the location of 

townships in the Gillette study area ...................................................................................11 

Figure 4. Map showing locations of surface coal mines and 7.5-minute quadrangle maps in the 

Gillette study area................................................................................................................12 

Figure 5. Map showing drill hole locations for stratigraphic data used in this study and locations of 

cross sections A-A’ through E-E’.......................................................................................16 

Figure 6. Representative stratigraphic sections showing coal assessed in the Gillette coal field, 

Wyoming .............................................................................................................................17 

Figure 7. West-east stratigraphic cross section A-A’ showing correlation of coal beds assessed in 

the northern part of the Gillette coal field ..........................................................................18 

Figure 8. West-east stratigraphic cross section B-B’ showing correlation of coal beds assessed in 

the northern part of the Gillette coal field ..........................................................................18 

Figure 9. Southwest-northeast stratigraphic cross section C-C’ showing correlation of coal beds 

assessed in the middle part of the Gillette coal field .........................................................19 

Figure 10. West-east stratigraphic cross section D-D’ showing correlation of coal beds assessed in 

 the southern part of the Gillette coal field.....................................................................19 

Figure 11. North-south stratigraphic cross section E-E’ showing correlation of coal beds assessed 

in the Gillette coal field....................................................................................................20 

Figure 12. Map showing areal distribution of the Wyodak rider, Upper Wyodak, Canyon, Lower 

Wyodak/Werner, and Gates/Kennedy coal beds...............................................................21 

2
Figure 13. Isopach map showing thickness of coal plus partings in the Wyodak rider coal-mining 

 unit ...................................................................................................................................22 

Figure 14. Isopach map showing thickness of coal plus partings in the Upper Wyodak coal-mining 

 unit ...................................................................................................................................23 

Figure 15. Isopach map showing thickness of rock above the Upper Wyodak coal bed........................23 

Figure 16. Isopach map showing thickness of coal plus partings in the Canyon coal-mining unit.........24 

Figure 17. Isopach map showing thickness of coal plus partings in the Lower Wyodak/Werner 

coal-mining unit ..................................................................................................................25 

Figure 18. Isopach map showing thickness of coal plus partings in the Gates/Kennedy coal-mining 

 unit ....................................................................................................................................25 

Figure 19. Map showing drill-hole locations for geochemical data.........................................................28 

Figure 20. Map showing features that restrict the area to be mined.........................................................32 

Figure 21. Map showing Federal coal ownership in and around the Gillette coal field..........................34 

Figure 22. Map showing ratios of waste rock to coal (stripping ratios)..................................................39 

Figure 23. Pie chart showing proportions of Wyodak rider, Upper Wyodak, Canyon, Lower 

Wyodak/Werner, and Gates/Kennedy coal beds that together compose the original 

coal resource in the Gillette coal field................................................................................41 

Figure 24. Gillette coal resource analysis results for the five coal beds...................................................42 

Figure 25. Bar graph showing resources in different resource categories for the combined five coal 

 beds in the Gillette coal field ...........................................................................................42

Figure 26. Histogram showing differences in the amounts of original, available, recoverable, and 

economic coal resources calculated for recent studies by the U.S. Geological Survey...43

Tables 

Table 1. Abbreviations and conversions......................................................................................................7 

Table 2. Names used in different publications for coal beds in the area of the Gillette coal field ...........8 

Table 3. Summary data of selected coal quality parameters for some coal beds in the Gillette coal 

field ......................................................................................................................................26 

Table 4. Summary of quality of coal supplied to coal-fired power plants in 2000 from mines in the 

Gillette coal field .................................................................................................................27 

Table 5. Proximate, ultimate, and calorific values for some coal beds assessed for this study in the 

Gillette coal field .................................................................................................................29 

Table 6. Values for trace elements considered to be potentially hazardous air pollutants, from

analyses of some coal beds assessed for this study in the Gillette coal field ...................29 

Table 7. List of factors that can restrict coal mining.................................................................................30 

Table 8. Original coal resources, previously mined resources, unavailable resources, available 

resources, mining losses, and recoverable resources of assessed coal beds in the 

Gillette coal field, reported in millions of short tons and by coal ownership category....38 

Table 9. Recoverable coal resources of all assessed coal in the Gillette coal field, reported by

stripping ratios.....................................................................................................................40 

Table 10. Economically recoverable coal resources of all assessed coal in the Gillette coal field, 

Powder River Basin, Wyoming..........................................................................................41 

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ABSTRACT 

The Powder River Basin, and particularly the Gillette coal field that contains the exceptionally thick 

Upper Wyodak coal bed, contains some of the largest deposits of low-sulfur subbituminous coal in 

the world (Molnia and Pierce, 1992). The Upper Wyodak coal, as well as other potentially minable 

coal in the Gillette coal field, was studied to determine how much coal is in the ground and how 

much of it could be economically extracted, given current and foreseeable economic factors and 

mining restrictions. We designed a hypothetical extraction plan to facilitate the computation of this 

estimate of recoverable and economic resources. This plan eliminates coal resources in areas of the 

coal field where mining could not take place due to various technological, societal, and 

environmental restrictions, and considers only the amount of coal that could be produced with 

current mining practices and equipment commonly used in the Powder River Basin. 

Coal-development considerations in the study area include railroads, Federal highways, pipelines, 

power lines, wildlife habitat, and alluvial valley floors. Some, but not all, of these factors can be 

mitigated so that surface mining of the coal could proceed. Geologic factors such as thick 

overburden, thin coal beds, sand channel wash-outs, faults, and areas of burned coal and surrounding 

rock (clinker) can require special equipment and mine plans that add to the cost of coal production. 

We estimated the original coal resource in the Gillette coal field, for all coal beds assessed and with 

no restrictions applied, to be 136.1 billion short tons. The estimates show that available coal, which 

is the part of the original coal resource that is accessible for mine development under current 

regulatory and land-use constraints, represents about 89 percent of the original resource. 

Recoverable coal, which is the available coal remaining after the coal is mined and processed, 

represents about 80 percent of the original coal resource. Economically recoverable coal, which is 

the recoverable coal that can be mined, processed, and marketed at a profit, represents only 1.3 

percent of the original resource at a coal sales price of $3.00 per ton, 5.1 percent at a sales price of 

$4.00 per ton; 10.4 percent at a l sales price of $5.00 per ton; 17 percent at a sales price of $6.00 per 

ton; and 32.8 percent at a sales price of $7.00 per ton. 

ACKNOWLEDGMENTS

This report was produced as a result of the efforts and cooperation of many people. Personnel 

within the U.S. Geological Survey (USGS) who assisted with this publication include Mark A. 

Kirschbaum, Neil S. Fishman, and Douglas J. Nichols who provided technical review and checked 

for accuracy of geologic names and ages and William R. Keefer, who provided a thorough edit of 

the manuscript. 

Allan M. Ochs, a geologist and contractor for the project, was the data base manager and worked 

with USGS personnel to correlate individual coal beds in the Gillette coal field. Tracey J. Mercier, a 

Geographic Information System (GIS) consultant from True North Mapping, produced many of the 

graphics used in this report. Gary McIntosh, of Slick Rock Software Design, provided customization 

and development of mine costing and economics software programs. 

Workers from other government agencies also assisted with various aspects of this report. Charlie 

Gaskill, of the U.S. Bureau of Land Management in Casper, Wyoming, supplied land-use 

information, and Edward Heffern, of the U.S. Bureau of Land Management in Cheyenne, Wyoming, 

supplied digital files delineating the eastern outcrops of the beds and areas containing clinker from

4
the burning of Wyodak coal beds. Dave Hutton, of the Wyoming Oil and Gas Conservation 

Commission in Casper, Wyoming, provided information on the locations and status of oil and gas 

wells within the study area. Norm Braz, of the U.S. Bureau of Land Management in Casper, 

Wyoming, supplied digital data that shows the extent of mined-out areas within the study area as of 

January 2000. 

Several software packages were used to accomplish this study. Any mention of these software 

packages are for descriptive purposes only and does not imply endorsement by the USGS.

INTRODUCTION AND OBJECTIVES 

Traditional USGS procedures to estimate national coal reserves use standardized mining recovery

factors that are applied throughout coal regions to obtain the estimated tonnage of recoverable coal. 

Those estimates are general in nature and do not take into consideration the amount of coal that 

cannot be mined because of environmental concerns, societal conflicts, site-specific geologic 

factors, coal loss due to mining and preparation technology, and economic constraints. Published 

studies by the USGS that include economic evaluations of extractable coal resources indicate that 

application of site-specific restrictions to estimates of available coal resources significantly reduces 

the amount of coal that is considered economically recoverable. 

This study of extractable coal in the Gillette coal field not only includes a resource analysis, but also 

applies an economic evaluation that is customized to the environmental, technological, cultural, and 

energy-related infrastructure of the Gillette coal field in the Powder River Basin, Wyoming (fig. 1). 

The economic recoverability aspect of the study considers the many restrictions that can affect the 

profitable extraction of coal. Mining production costs, current mining machinery and methods, coal 

transport to the market place, present and near-future market conditions, and the gross calorific 

value, ash yield, and sulfur content of the available coal are all factors that influence the amount of 

coal that can be mined at a profit. 

This detailed information regarding the amount of coal that can be economically produced 

contributes to the body of knowledge that can be used to make local, State, and Federal energy and 

land-use policy decisions. In addition, this information can aid government and other planners in 

determining the possible socio-economic effects on their regions as coal resources are developed and 

eventually become depleted. 

PREVIOUS COAL RESOURCE CALCULATIONS IN THE GILLETTE AREA 

There have been a number of previous studies that have estimated coal resources in the Powder 

River Basin. Such studies have used various defined study areas and have included different coal 

beds or coal zones. There have been a multitude of purposes for which resources are calculated, and 

there have been differences in criteria, such as variations in coal thickness and overburden 

categories, used for calculation. There have also been changes in calculation methods themselves. 

The earliest estimate of coal resources in the Gillette coal field was by Dobbin and others (1927, p. 

20). They estimated the tonnage of the Gillette coal field to be 14.4 billion short tons (bst). The area 

included in their coal field designation was about 3,000 sq mi, twice the 1,500 sq mi area of this study

(see table 1 for conversion to metric units and other values). However, they used only outcrop 

5
measurements for their calculation and were not able to model subsurface coals; almost no subsurface 

data was available at that time. 

Berryhill and others (1950) provided a calculation of total original reserves of subbituminous coal in 

Wyoming by township, overburden thickness, and coal bed thickness. Coal tonnage estimates given 

for 86 townships entirely or partly within the Gillette coal field total about 45 bst. Coal beds included 

in that estimate were not limited to the Wyodak-Anderson stratigraphic interval, but included all beds 

greater than 2.5 ft thick, with overburden less than 2,000 ft. Berryhill’s estimates are the sum of 

measured, indicated, and inferred reserve tonnages (as defined by Berryhill and others, 1950) for these 

townships. 

Trent (1986) published an estimate of 225 billion tons of non-leased, Federal coal in the quadrangles that 

fall within the Gillette coal field, included were coal beds greater than 5 ft thick at depths of less than 

3,000 ft. No resources were included for leased Federal coal, State coal, fee (private) coal, or lands 

6
encompassed by coal prospecting permits and preference right lease applications. Coal beds included in 

Trent’s estimate were not limited to those beds within the Wyodak-Anderson stratigraphic interval. 

Table 1. Abbreviations and conversions. All tonnage measurements are given in short tons 

To convert from To Multiply by 

Feet (ft) Meters (m) 0.3048 

Miles (mi) Kilometers (km) 1.609344 

Square miles (sq mi) Square kilometers (sq km) 1.609344 

Pounds (lbs) Kilograms (kg) 0.4536 

Short tons (2,000 lbs) Metric tons (2,204.6 lbs) 0.90718474 

Millions of short tons (mst) Short tons 1,000,000 

Billions of short tons (bst) Short tons 1,000,000,000 

Acre-feet Short tons of subbituminous coal 1,750 

Ayers (1986) published an estimate of 1.06 trillion tons of coal in the Tongue River Member of the Fort 

Union Formation within the Wyoming part of the Powder River Basin. He included coal beds greater 

than 2 ft thick to depths of less than 3,000 ft. 

Glass (2001) published an estimate of 1.03 trillion tons of coal for the Wyoming part of the Powder 

River Basin, which included coal beds of any thickness and to all depths, even greater than 6,000 ft. 

Glass (2001) also estimated remaining strippable reserve base for the Wyodak coal bed to be 17.9 bst, 

using a 200-ft cut-off depth for overburden. This is the largest reserve base for any single coal bed in 

Wyoming. 

Ellis and others (1999) published an estimate of 110 bst of coal in the Wyodak- Anderson coal zone, as 

defined by the Fort Union Coal Assessment Team (1999), within the Gillette coal field. That estimate 

was derived from stratigraphic data interpreted from electric logs that were run in about 2,000 drill-hole 

locations. Resources were calculated using total coal thickness, the sum of all coal beds over 2.5 ft 

thick, for all coal beds included in the zone (table 2). All of the coal was assumed to be subbituminous 

in rank, with a conversion factor of 1,770 short tons of coal per acre-foot. Parting material, coal less 

than 2.5 ft in thickness, coal above or below Wyodak-Anderson clinker, and coal within active lease 

areas were not included in the resource calculations. 

Comparison of the previous resource estimates shows the usefulness of periodically recalculating coal 

resources for an area when more and better data become available over time. The economic coal 

recoverability calculations in the present report are a refinement of previous coal resource studies in 

the Gillette coal field. Our estimates include data on how much of the total coal resource (1) has 

already been mined, (2) could be produced using specific mine models, and (3) could be produced at a 

profit at given market values. These more specific resource calculations add to the body of knowledge 

available for State and Federal agencies to determine the amount of coal that could actually be 

produced within the Gillette coal field, thereby contributing to decisions regarding energy policy and 

future land use. 

7
Table 2. Names used in different publications for coal beds in the area of the Gillette coal field. The beds in the WyodakAnderson coal zone are listed from upper to lower; however, many of the beds are only in certain parts of the coal field, 

stratigraphically equivalent, or splits of other beds 

Montana 

name 

Kent and 

others, 

1980a 

Pierce and 

others, 1990 

Fort Union Coal Assessment 

Team, 1999, and Glass, 1999 

Molnia and 

others, 1997, 

1999, and 

Osmonson, 

2000 

This report 

Smith Roland/Badger Smith Wyodak rider 

Not 

applicable 

Upper Wyodak Wyodak or upper 

Wyodak

(AndersonCanyon) 

Wyodak-Anderson coal zone= 

Swartz, Badger, School, 

Sussex, Big George, Wyodak, 

Anderson, Dietz

Main Wyodak Upper Wyodak 

Canyon Canyon Canyon

Cook Werner Lower Wyodak Werner Lower

Wyodak/Werner 

Wall Gates Upper

Pawnee Kennedy Kennedy Gates/Kennedy

Cache Carson

DEFINITIONS 

The present study includes determinations of original, available, recoverable, and economically

recoverable (extractable) resources, a terminology that has been used in many USGS coal studies 

(see Carter and Gardner, 1989; Eggleston and others, 1990; Molnia and others, 1999; Osmonson and 

others, 2000). The following definitions were applied in our resource evaluation: 

• Original resource—The total amount of coal tonnage in the ground prior to mining. 

• Available resource—That part of the original coal resource that is accessible for mine 

development under current regulatory and land-use constraints. Alluvial valley floors 

and producing oil and gas wells are examples of constraints that may restrict coal mining 

in their immediate vicinities. The available resource does not include coal that has been 

previously mined. 

• Recoverable resource—That part of the available coal that is left after mining losses and 

cleaning losses are subtracted. Costs involved with the extraction and cleaning of the 

coal are not considered, nor is the potential selling price of the coal. 

• Economically recoverable resource—That part of the recoverable coal that can be mined, 

cleaned, and marketed at a profit (depends on the mine location, the characteristics of the 

coal bed, the quality of the coal, and the mining methods used). Also known as a 

reserve. 

The present report contains many different measurements and abbreviations. Table 1 shows 

conversions for measurements used. All coal resource numbers are reported in short tons. 

For the purpose of this study the term coal bed is used for coal bodies with no parting. The term

coal unit is used for the assessed coal and includes coal beds plus parting material. This represents 

the stratigraphic interval used for the coal resource calculations. Additionally, when the term

Gillette coal field is used we are only referring to the area in which economically recoverable coal 

resources were calculated. This differs from the Gillette study area, which includes area outside of 

the coal field. Considering data from drill holes outside of the coal field was essential to the 

8
correlation of coal beds and to the 

production of accurate coal thickness 

and overburden isopach maps used in 

this study. 

GEOLOGIC SETTING AND STUDY 

AREA 

The Powder River Basin covers about 

22,000 sq mi in northeastern Wyoming 

and southeastern Montana (fig. 1). The 

axis trends northwest- southeast, near 

the west edge, and the basin floor is 

markedly asymmetrical with steep dips 

on the west side and gentle dips on the 

east. 

The Wasatch Formation (Eocene) 

covers about one-third of the Powder 

River Basin, with the underlying Fort 

Union Formation (Paleocene) exposed 

at the surface along the basin 

boundaries. Within the Wyoming part of 

the Powder River Basin, the Wasatch 

contains coal beds that have heat values, 

agglomeration characteristics, and fixed 

carbon and volatile matter content that 

place them as subbituminous C in 

apparent rank (Glass, 2001). These coal 

beds, some of which are 

stratigraphically equivalent to each 

other, are named (from younger to 

older): (1) the Lake de Smet, which 

occurs in the northwest and splits into 

the Walters, Healy, Schuman, Timar, 

Cameron, Dry Creek, Murray, and 

Ucross beds to the east; (2) the Ulm1, Ulm 2, and Scott beds that occur in the north; (3) the Felix, 

which is found in many places within the Wyoming part of the basin; and (4) the Badger, and School 

beds, which are in the south. The Wasatch conformably overlies the Fort Union in the center of the 

basin and unconformably overlies the Fort Union along the basin margins (fig. 2). The boundary

between the two formations is generally placed above the Roland coal bed (table 2). 

Rocks in the Fort Union Formation lie unconformably lie on the Lance Formation (Upper 

Cretaceous) (fig. 2). The Fort Union Formation in Wyoming is made up of three members, from

upper to lower: the Tongue River Member, the Lebo Member, and the Tullock Member. The 

Formation (fig. 1) contains some of the thickest and most extensive deposits of low-sulfur 

subbituminous coal in the world (Molnia and Pierce, 1992), most of which is from the WyodakAnderson coal zone in the Tongue River Member (Fort Union Coal Assessment Team, 1999). These 

9
coal beds, some of which are stratigraphically equivalent to each other, are named (from younger to 

older): the Swartz, Badger, School, Sussex, Big George, Wyodak, Anderson, Dietz, Canyon, and 

Werner. 

The Gillette coal field (figs. 1 and 3) encompasses about 1,500 sq mi in the east-central part of the 

Powder River Basin in Campbell County, Wyoming. The east boundary is based on the WyodakAnderson coal outcrop and Wyodak-Anderson clinker (Kent and Berlage, 1980; Heffern and others, 

1993; Heffern and Coates, 1999; and Coates and Heffern, 1999). In areas to the east and northeast, 

where outcrop and clinker information was not available and where coal beds assessed for this study

were not present in drill holes, the coal field boundary was refined using the contact between the 

Wasatch Formation and the Fort Union Formation shown in maps by Kent and Berlage (1980) and 

Boyd and Ver Ploeg (1997). The north and south boundaries of the study area were delineated by

the closest township and range lines that encompassed the area of active mining around Gillette (T. 

40-52 N. and R. 69-73 W.). The west boundary, at R. 73 W., corresponds to the west boundary used 

for the coal resource assessment of the Gillette coal field by Ellis and others (1999). Figure 4 shows 

the mines in the Gillette coal field, and the 7.5-minute quadrangle maps that are within the study

area. 

In the Gillette study area, rocks dip 2 to 3 degrees to the west (Ellis and others, 1999). The Fort 

Union Formation is at the surface in most locations. Coal within the Tongue River Member of the 

Fort Union is as much as 200 ft thick in the area and the coal beds merge, split, and are cut out by

channels within short distances (Ellis and others, 1999). Stratigraphic relations are complex and 

correlations of individual beds are difficult. The named coal beds assessed in this report are the 

Wyodak rider, Upper Wyodak, Canyon, Lower Wyodak/Werner, and Gates/Kennedy. The 

relationship of these beds to the beds in the Wyodak-Anderson coal zone is shown on table 2. 

COAL MINING 

Coal mining in the Powder River Basin began in 1883 near the cities of Glenrock and Douglas, in the 

southern part (fig. 1). The development of railroad lines in 1886 and 1887 influenced growth in 

mining activity. The first mines were underground, with the Inez Mine near Douglas and the Deer 

Creek Mine near Glenrock each producing about 13,000 short tons of coal in 1888 (Gardner and 

Flores, 1989). The Cole Creek, Buffalo Fuel Company, and Dietz Mines opened soon after. By 1925 

there were 17 additional underground mines opened in Sheridan County. In 1905, mines in Sheridan 

County were producing about 550,000 tons of coal annually (Trumbull, 1905). The first strip mine, 

the Peerless Mine near Gillette, Wyoming, was opened in 1924 (Gardner and Flores, 1989) and a 90-

ft- thick bed was mined. Soon after, a large strip mine, the Wyodak Coal and Manufacturing 

Company, opened and in 1925 produced about 33,600 short tons of coal. By the mid-1900s 

advancements in strip mining equipment and mining techniques made strip mining much more 

profitable. Most underground mines closed or the companies switched over into surface mining 

ventures. 

10
11
Prior to 1950 most coal was used for locomotive fuel, with minor amounts used to fuel power plants, 

sugar factories, and cement plants, or used for local heating (Mapel, 1958). In the 1960s, because of 

the national need for additional electrical energy, power plants were built adjacent to the producing 

mines. At that time coal utilization shifted from railroad fuel to fuel for power generation. 

In 1999, nine of the ten coal mines with the largest production in the United States were located in 

the Gillette coal field (Glass, 2001). All production from these mines is through surface mining 

methods. Year 2000 production from all of the mines in the Gillette coal field contributed about 30 

12
percent (about 323 million of short tons (mst)) of the total 2000 coal production of 1,075 mst 

(Resource Data International, 2002). The Gillette coal field contains 12 active coal mines (fig. 4), all 

producing from the Tongue River Member of the Fort Union Formation (Resource Data 

International, Inc., 2002). 

OTHER ENERGY COMMODITIES IN THE AREA

Energy commodities currently being developed in the Powder River Basin, in addition to coal, are 

conventional oil and gas and coalbed methane. Although coalbed methane is a gas, we discuss it 

separately, because there are potential conflicts and concerns specific to the development of that 

resource that do not apply to conventional oil and gas development. 

Powder River Basin oil and gas development began in 1887, with the discovery of an oil and gas field 

near Moorcroft, Wyoming. There are currently more than 35,000 oil and gas wells within the area of 

the Gillette coal field (IHS Energy Group, 2001). Current infrastructure for production and transport 

of oil and gas in the area includes roads, pipelines, pump houses, separators, and several gasprocessing plants. Generally, there is little conflict between coal development and conventional oil 

and gas development in the Powder River Basin. Conventional oil and gas development is primarily

from stratigraphic units below the extractable coal seams. Additionally, conventional oil and gas 

development is primarily in the central part of the basin, whereas the coal mining is along the basin 

margins. Where oil and gas development and coal mining occur in the same areas, mining is 

confined to areas outside a specific buffer distance from wells, pipelines, and other oil and gas related 

structures. 

Coalbed methane development in the Powder River Basin began with two wells in 1981 and, as of 

July 20, 2001, a total of 18,578 wells had been drilled or been permitted to be drilled (Wyoming Oil 

and Gas Conservation Commission, 2001). Resource specialists estimate that over 50,000 coalbed 

methane wells will be drilled in the next 20 years. The production life of a coalbed methane well, 

which depends on the distance of the well from adjacent wells and how much methane is in the coal, 

is estimated to be from 10 to 12 years, although production from multiple seams can extend the life of 

the well by another 10 to 30 years (De Bruin and others, 2002). 

To produce coalbed methane, a large volume of groundwater is released from the coal. The 

groundwater can be discharged to holding ponds for consumption by livestock, discharged to existing 

drainage systems, released into the atmosphere through the use of misting towers, or re-injected into 

another stratigraphic unit. Concerns regarding possible contamination of existing surface water, the 

quality of water in holding ponds, the production of saline crust on the ground surface, the lowering of 

the water table, and possible contamination or depletion of groundwater in existing aquifers are 

currently being studied and addressed in the Powder River Basin. 

Conflicts have arisen between coal mining and coalbed methane development. One conflict involved 

the ownership of coalbed methane- whether it belonged to the owner of the oil and gas estate or the 

owner of the coal estate. The U.S. Supreme Court resolved this in 1999, when they ruled that coalbed 

methane is part of the oil and gas estate. In addition, the court specified that the owner of the methane 

leases has the right to gain access and to develop their estate, and that owners of the land surface 

should be adequately compensated for damage to their property resulting from methane extraction. 

There has undoubtedly been a large volume of coalbed methane that has been lost due to previous 

13
mining of coal in the Gillette coal field. It is anticipated that (1) coalbed methane extraction in a 

given area will have priority over coal mining; and (2) if coal mining precedes methane extraction, the 

owners of coalbed methane leases may have to be compensated for lost gas. A current joint USGS 

and Bureau of Land Management (BLM) cooperative project is attempting to estimate the amount of 

gas that has been lost due to previous and current mining within the area of coalbed methane leases 

(Flores and others, 2001). Results of this study have been posted on a BLM website (at 

www.wy.blm.gov/minerals/og/res.mgt.html). The Wyoming congressional delegation is also trying to 

determine ways to arbitrate conflicts between the coalbed methane and coal industries (DeBruin and 

others, 2002). 

COAL BED GEOLOGY 

Coal Bed Nomenclature 

Correlation of individually named coal beds across the entire Powder River Basin is difficult. The 

fluvial systems responsible for deposition of the coal beds created pinch-outs, splits, wants, channels, 

and bed mergers (Flores and others, 1999). Ayers (1986) states: “Attempts to correlate seams 

across an entire basin are not only futile, but are also counter to our understanding of the existing 

coal depositional systems.... Previous studies.... show that the boundaries of Tongue River coal 

seams are established by the framework elements of the host sediments. Most coal seams are 

continuous over distances of tens of miles (commonly 30 to 50 miles).” 

This difficulty in correlating individual beds throughout the Powder River Basin also applies to 

correlating the beds throughout the Gillette coal field, despite the numerous attempts to identify,

trace, and name beds locally. Table 2 shows some of the names used for coal beds and zones within 

the area. A report by Kent and others (1980), covering the northernmost part of our study area that 

falls within the Spotted Horse coal field of Olive (1957), established a coal-bed nomenclature system

that has become the standard for much of the Powder River Basin in Wyoming. As described below, 

they retained certain existing coal-bed nomenclature and revised other nomenclature by introducing 

new coal-bed names. Pierce and others (1990), in another report, covered the southwestern part of 

our study area and extended the use of coal bed names from Kent and others (1980). 

Kent and others (1980) retained and used coal bed names as defined by Olive (1957) for the Spotted 

Horse coal field. In descending order, these names are Felix, Arvada, Roland (Baker, 1929), Smith, 

Anderson, and Canyon. Kent and others (1980) also (1) recognized the Swartz coal bed of McKay

and Mapel (1973) as occurring between the Smith and Anderson coal beds in certain areas; and (2) 

used the name Wyodak in the sense of Mapel (1973), which refers to the 90-ft-thick coal bed 

exposed by surface mining about 5 miles east of Gillette, Wyoming. 

Names of coal beds below the Canyon coal-- the Cook, Wall, Pawnee, and Cache-- were not retained 

by Kent and others (1980) in the Spotted Horse coal field because those names originated in 

Montana coal fields at locations many miles from the Spotted Horse coal field of Wyoming and 

direct correlations were not warranted in their view. Also, previous workers had used the Wall name

to represent different beds in different coal fields. For these reasons, Kent and others (1980) decided 

to introduce a new set of names (table 2). They explained that “Many regional coal-correlation 

problems remain unresolved and usage of Montana names such as Cook, Wall, Pawnee or Cache to 

identify coal beds in the Recluse (Wyoming) area implies coal-correlations that have not yet been 

established. In order to avoid those implications, these Montana names are subordinated.... and new 

names are introduced here for certain coal beds below the Canyon.... The names selected are those 

14
of owners of ranches near the reference sections.” 

For the northernmost part of our study area, we used Kent and others (1980) to make the following 

correlations: 

• Wyodak rider is equivalent to the Smith coal bed 

• Upper Wyodak contains Smith, Swartz, and Anderson, where there is no separate Wyodak 

rider. 

• Canyon occurs in very limited areas and is an upper split of the Lower Wyodak coal bed. 

The lower split, or the main part of the Lower Wyodak/Werner coal bed, contains the 

Werner coal bed. 

• Gates/Kennedy occurs below the Lower Wyodak/Werner coal bed. 

Pierce and others (1990) used the coal bed nomenclature of Kent and others (1980) as discussed 

above, and continued that nomenclature southward into the southern Powder River Basin. Their 

publication covers the southwestern part of the Gillette coal field; for that area, we used Pierce and 

others (1990) to make the following correlations: 

• Wyodak rider is their Roland coal bed 

• Upper Wyodak is the Anderson-Canyon coal bed 

• Gates/Kennedy occurs below the Lower Wyodak coal bed. 

The differences between the correlations we made from Kent and others (1980) and those made from

Pierce and others (1990) reflect the distance between their study areas and the changes in coal 

depositional systems from the northern part to the southern part of the Powder River Basin, 

Wyoming. 

Flores and others (1999 [Chapter PF]) defined a coal zone called the Wyodak-Anderson coal zone in 

the Powder River Basin, which includes many named coal beds in the upper part of the Tongue 

River Member of the Fort Union Formation. Coal beds in this coal zone are, from top to bottom, the 

Smith, Swartz, Badger, School, Sussex, Big George, Wyodak (which includes the Lower 

Wyodak/Werner and Upper Wyodak of this report), Anderson, Dietz, Canyon, and Werner (table 2). 

Some of these beds are splits of other beds or are stratigraphically equivalent to other beds. 

Additionally, many of the beds are found only in certain parts of the basin. The Smith, Anderson, 

Wyodak, and Canyon beds are mined at the surface in the Gillette coal field. 

Coal Bed Correlations 

The data set containing stratigraphic information used by us for resource calculations and for 

geologic characterizations includes 1,798 data points within the Gillette coal field and 448 data 

points within a three-mile-wide band surrounding the field (fig. 5). Data we used was obtained from

Flores and others (1999) and was generated by the Fort Union Coal Assessment Team as part of the 

USGS National Coal Resource Assessment. They correlated the top and base of the WyodakAnderson coal zone in many of the drill holes that we used in our Gillette coal field study (fig. 5). 

For our study of economically extractable coal we correlated and modeled individual beds to both 

within and outside of the Wyodak-Anderson coal zone, as defined by Flores and others (1999), to 

determine feasibility of extraction. The five coal beds in the Gillette coal field that were modeled for 

extraction, and for which resources were calculated are: the Wyodak rider, Upper Wyodak, Canyon, 

Lower Wyodak/Werner, and Gates/Kennedy. Not all drill holes in our data set encountered all five 

of the coal beds. 

15
In the southern part of the study area, we correlated the Wyodak rider with the Roland coal bed, as 

recognized by Pierce and others (1990) (table 2). The Roland coal bed is not included in the 

Wyodak-Anderson zone; however, in the southern part of the study area the Roland coal bed is found 

in the same general stratigraphic position as the Smith coal bed, which is included in the zone, and 

the Smith bed is absent. Thus we correlated the Wyodak rider coal bed to the Roland coal bed in the 

southern part of the Gillette coal field, and it served as the top of our studied stratigraphic interval in 

16
that part of the field. Our study also included the Gates or Kennedy coal beds, referred to here as the 

Gates/Kennedy coal bed, which occurs below the Werner coal bed, and is the lowermost coal bed in 

the Wyodak-Anderson coal zone as recognized by Flores and others (1999). In our study, we 

included the Gates/ Kennedy coal bed in those places where the coal is a thick and relatively

continuous coal bed that could be mined with the coal beds above it. Figure 6 includes two columnar 

sections that represent the general stratigraphic relations of coal beds assessed in the Gillette coal 

field. Figures 7, 8, 9, 10, and 11 show cross sections in various parts of the study area that give a 

more detailed picture of the complex stratigraphic relations of the coal beds that were assessed. 

17
18
19

The following are brief descriptions of the coal beds that were assessed in the Gillette coal field. The 

given thickness of each is that of the coal-mining unit, which is that of the coal plus the parting 

material.

 

Wyodak rider: 

This bed occurs as a 

rider splitting from the 

Upper Wyodak bed. It 

is continuous 

throughout the northern 

three-quarters of the 

study area, with a lateral 

extent of approximately

747 sq mi (fig. 12). The 

bed ranges from 3 ft to 

just over 30 ft in 

thickness and 

commonly includes 1 to 

3 partings varying from

0.5 ft to 4 ft thick (fig. 

13). Overburden ranges 

from zero at the outcrop 

to 1,091 ft along the 

west side of the Gillette 

coal field. 

Upper Wyodak: 

The thickest and most 

contiguous of the coal 

beds studied, the Upper 

Wyodak occurs 

everywhere in the coal 

field except for a small 

area in the southwestern 

corner, covering a total 

of about 1,440 sq mi

(fig. 12). This bed is 

equivalent to the Main Wyodak coal bed that was included in coal availability and 

recoverability studies in the Hilight quadrangle (fig. 4) by Molnia and others (1997, 1999) 

and Osmonson and others (2000). The Upper Wyodak coal bed ranges from 0 ft to 172 ft in 

thickness (fig. 14) and includes as many as five partings. The partings consist mostly of 

claystone, ranging from 1 ft to 20 ft in thickness. The thicker partings occur mostly in the 

northern one-third of the study area. The continuity of the bed is shown in figures 8, 9, 10, 

and 11. Thinning of the bed toward the west is an artifact of the bed splitting into the Lower 

Wyodak/Werner coal bed, as shown in figures 8 and 10, and of a general stratigraphic 

thinning trend. Overburden ranges from zero at the outcrop to 1,447 ft (fig. 15) along the 

west side of the coal field. 

21
22

Canyon: 

The Canyon bed is the most 

areally limited bed that is 

mined in the Gillette coal 

field. It splits from the 

Lower Wyodak/Werner to 

become a bed above it, and 

covers only about 120 sq 

mi. The pod nature of this 

bed is evident in figure 12, 

although the bed becomes 

more continuous to the 

northwest. The bed reaches 

thicknesses of about 40 ft, 

and commonly includes 2 

or 3 mudstone partings that 

are 3 ft to 8 ft thick (fig. 

16). Cross sections in 

figures 7, 8, and 11 show 

the Canyon bed splitting 

from the Lower 

Wyodak/Werner coal. 

Overburden ranges from

112 ft in the eastern part of 

the coal field to 1,225 ft in 

the western part. 

Lower Wyodak/Werner: 

The Lower Wyodak/Werner 

bed is a lower split from the 

Upper Wyodak coal bed. It 

covers an area of about 875 

sq mi (fig. 12). Thickness 

ranges from 10 ft to 120 ft, 

with the thickest part occurring in the northern part of the field. One to five partings are 

common, ranging from 0.5 ft to 25 ft in thickness. Figure 17 shows the thickness of the coal 

bed plus partings. The large blank areas on the eastern limit of the coal field are split lines 

where this bed merges with the Upper Wyodak coal. Cross sections in figures 8, 9, 10, and 

11 show the Lower Wyodak/Werner coal splitting from the Upper Wyodak in the northern 

part of the coal field and thinning to a featheredge in the southern part. Overburden ranges 

from zero at the outcrop along its eastern extent to a maximum of 1,577 ft to the west. 

Gates/Kennedy: 

The Gates/Kennedy bed, as correlated in this study, covers approximately 209 sq mi in the 

northern part of the coal field (fig. 12). The bed attains thicknesses of as much as 42 ft, 

including 1 or 2 partings that are 2 to 11 ft thick (fig. 18). The thickness of the coal plus 

partings is shown on figure 18. Overburden ranges from 771 ft along its eastern extent to a 

maximum of 1,713 ft to the west.

24

COAL GEOCHEMISTRY

Coal from the Fort Union Formation in the Gillette coal field is generally considered to be clean, and 

compliant with SO2 emissions standards (U.S. Environmental Protection Agency, 1996). The Clean 

Air Act mandates that coal-fired power plants not release emissions containing more than 1.2 pounds 

of SO2 per million Btu. The low content of sulfur in coal from the Powder River Basin (Stricker and 

Ellis, 1999), and specifically within the Gillette coal field (Ellis and others, 1999), makes this coal an 

excellent product for mixing with noncompliant coal from other areas. 

Coal quality in the Wyodak-Anderson coal zone in the Gillette coal field study area reported by Ellis 

and others (1999) included analyses from a total of 108 locations. The weighted average of values 

from each data point location indicates total sulfur content of from 0.20 to 1.16 percent, with a mean 

of 0.48 percent and ash content of from 3.5 to 25.06 percent, with a mean of 7.45 percent. For 

comparison, low total sulfur content is considered to be less than or equal to 1 percent by weight and 

low ash yield is considered to be less than or equal to 8 percent by weight (Wood and others, 1983). 

Pounds of SO2 per million Btu for Wyodak-Anderson coal ranges from 0.44 to 3.27 with a mean of 

1.25. The gross calorific value of the coal samples ranges from 3,740 to 9,950 Btu/lb, with a mean 

of 8,220 Btu/lb. More detailed information on coal quality of the coal within the Wyodak-Anderson 

coal zone is given in Stricker and Ellis (1999) and Ellis and others (1999). 

Other coal analyses for coal beds that are at least partially correlative to the beds assessed in this 

study include those reported by Glass (2001), such as the Wyodak, Anderson, Canyon, and Smith. 

Coal thickness ranges and analytical values for these beds are shown in table 3; all are 

subbituminous C in apparent rank. The Canyon and Anderson beds, which have been identified in 

the western part of the coal field, coalesce to the east to form the thick Upper Wyodak coal bed 

(table 2). 

Table 3. Summary data of selected coal quality parameters for some coal beds in the Gillette coal field, Powder River 

Basin, Wyoming. Data are from Glass (2000) and are listed according to the coal bed names used in that report. Table 2 

indicates the relations of these beds to the coal beds assessed in our report. All values are on an as-received basis. 

Data Coal beds 

Anderson Canyon Wyodak Smith 

Coal thickness range (ft) 10-50 11-65 25-190 5-20

Number of samples 9 9 59 1 

Moisture range (percent) 24.9-34. 26.5-31.5 21.1-36.9 31.8 

Mean moisture (percent) 29.5 29.6 29.8 31.8 

Ash range (percent) 3.5-12.2 3.1-7.4 3.9-12.2 4.7 

Mean Ash (percent) 6.5 5.1 6.0 4.7 

Total sulfur range (percent) 0.17-1.13 0.14-0.92 0.2-1.2 0.63

Mean total sulfur (percent) 0.52 0.34 0.5 0.63 

Heat value range (Btu) 7,130-8,740 7,540-8,610 7,420-9,600 7,990 

Mean heat value (Btu) 7,900 8,290 8,220 7,990 

Fixed carbon range (percent) 29.0-38.0 31.8-38.4 29.6-41.4 34.8

Mean fixed carbon (percent) 33.9 34.6 33.5 34.8 

Volatile matter range (percent) 26.5-34. 28.7-33.3 26.5-35.5 28.7 

Mean volatile matter (percent) 30.1 30.7 30.7 28.7 

About 300 million short tons of coal were supplied in 2000 to coal-fired power plants from the in the 

Gillette coal field (fig. 4) (Resource Data International, 2002). According to the 2002 COALdat 

database (Resource Data International, Inc., 2002), the average coal quality of Fort Union Formation 

26
coal supplied to electrical power plants in 2000 from mines in the Gillette coal field was 0.34 percent 

total sulfur, 5.17 percent ash, 0.79 pounds of SO2 per million Btu, and 8,530 Btu/lb. The quality of 

coal produced from these mines, reported by sub-areas in the Gillette coal field, is shown in table 4. 

Table 4. Summary of quality of coal supplied to coal-fired power plants in 2000 from mines in the Gillette coal field 

(Resource Data International, Inc., 2002). Data are listed by the location of mines within the coal field (fig. 2). The 

“combined” category is coal that was supplied to power plants from mines located in different parts of the coal field. 

Proximate, ultimate, and heat of combustion values are reported on an as-received basis. Btu is British thermal units. 

Coal quality parameter Northern 

part 

Middle 

part Southern part Combined areas 

From all of 

the mines 

Minimum ash (percent) 5.01 4.44 4.41 4.67 4.41 

Maximum ash (percent) 6.68 5.51 5.31 5.0 6.68 

Mean ash (percent) 5.64 5.14 5.00 4.83 5.17 

Minimum total sulfur (percent) 0.36 0.31 0.20 0.33 0.20 

Maximum total sulfur (percent) 0.56 0.35 0.38 0.33 0.56 

Mean total sulfur (percent) 0.43 0.33 0.29 0.33 0.34 

Minimum gross calorific value (Btu) 8,056 8,342 8,568 8,433 8,056 

Maximum gross calorific value (Btu) 8,342 8,596 8,875 8,820 8,875 

Mean gross calorific value (Btu) 8,198 8,487 8,755 8,627 8,529 

Minimum lbSO2/million Btu 0.89 0.71 0.45 0.75 0.45 

Maximum lbSO2/million Btu 1.40 0.83 0.87 0.79 1.40 

Mean lbSO2/million Btu 1.04 0.77 0.65 0.77 0.79 

For the individual coal beds we studied, there were a limited number of analyses available. Figure 

19 shows the sample locations. The coal quality data set for this study is made up of 140 coal 

samples that were analyzed for proximate, ultimate and heat-of combustion values, and 157 coal 

samples that were analyzed for selected potentially environmentally hazardous trace elements. 

Represented in the suite of samples were the Wyodak rider, Upper Wyodak, and Lower 

Wyodak/Werner beds. These were no analyses from the Canyon or Gates/Kennedy beds. Tables 5 

and 6 show minimum, maximum and mean coal quality values for these analyses. A more detailed 

discussion of coal quality in the Powder River Basin and in the Gillette coal field can be found in 

Ellis (2002). 

27
28
Table 5. Proximate and ultimate analyses and heat values, on an as-received basis, for coal assessed for this study in the 

Gillette coal field, Powder River Basin, Wyoming. Data were not available for the Canyon or the Gates/Kennedy coal beds. 

Parameter Data Wyodak 

rider 

Upper 

Wyodak 

Lower 

Wyodak/Werner 

All assessed 

coal units 

Moisture (percent) Minimum 20 15 25 15 

 Maximum 27 35 32 35 

 Mean 23 27 27 27 

Ash (percent) Minimum 9.7 2.5 4.2 2.5 

 Maximum 19.1 19.68 8.2 19.68 

 Mean 12.90 5.80 5.83 6.01 

Total sulfur Minimum 0.80 0.13 0.20 0.13 

 (percent) Maximum 1.50 2.30 0.40 2.30 

 Mean 1.13 0.46 0.27 0.46 

Lb SO2/million Minimum 0.35 0.25 1.45 0.25

 Btu Maximum 0.71 3.68 3.02 3.68 

 Mean 0.55 1.70 2.40 1.73 

Calorific value Minimum 7,890 7,170 7,576 7,170 

 (Btu) Maximum 9,409 9,950 8,980 9,950 

 Mean 8,500 8,569 8,472 8,554 

Moist, mineral- Minimum 9,156 8,246 8,311 8,246 

 matter free Btu Maximum 10,562 10,572 9,407 10,572 

 Mean 9,879 9,193 9,039 9,211 

Fixed carbon Minimum 29.7 25.5 4.1 4.1 

 (percent) Maximum 33.1 44.5 39.3 44.5 

 Mean 30.8 35.0 33.6 34.8 

Volatile matter Minimum 30.30 24.75 28.80 24.75 

(percent) Maximum 37.80 37.80 55.70 55.70 

 Mean 33.23 31.71 33.50 31.87 

Table 6. Values for trace elements considered potentially hazardous air pollutants in analyses of assessed coal from the 

Gillette coal field, Powder River Basin, Wyoming. Data are from the Economic and Environmental Evaluation of 

Extractable Coal Resources (E4CR) database. The E4CR dataset does not contain data for the Canyon or 

Gates/Kennedy coal units. All trace element contents are reported in parts per million and are on a whole-coal and 

remnant-moisture basis. 

Potentially Hazardous Air Pollutant Trace Elements 

Parameter Data Wyodak rider Upper 

Wyodak 

Lower Wyodak/ 

Werner 

All coal units 

 Arsenic Minimum 3.6 0.35 0.33 0.33 

 Maximum 65 30 3 65 

 Mean 20 2.1 0.88 2.5 

 Lead Minimum 2.4 0.14 0.76 0.14 

 Maximum 7.7 14 7.6 14 

 Mean 5.04 2.5 2.9 2.5 

 Mercury Minimum 0.14 0.02 0.02 0.02 

 Maximum 0.35 3.8 0.16 3.8 

 Mean 0.26 0.21 0.07 0.20 

 Selenium Minimum 1.5 0.05 0.18 0.05 

 Maximum 2.2 6.7 1.7 6.7 

 Mean 1.8 1.01 0.59 1.01 

 Uranium Minimum 1.4 0.08 0.01 0.01 

 Maximum 2.9 3.2 1.2 3.2 

 Mean 2.1 0.61 0.46 0.64 

29
 

Potentially Hazardous Air Pollutant Trace Elements 

Parameter Data Upper 

Wyodak 

Lower Wyodak/ 

Werner 

Wyodak rider All coal units 

 Arsenic Minimum 0.35 0.33 3.6 0.33 

 Maximum 30 3 65 65 

 Mean 2.1 0.88 20 2.5 

 Lead Minimum 0.14 0.76 2.4 0.14 

 Maximum 14 7.6 7.7 14 

 Mean 2.5 2.9 5.04 2.5 

 Mercury Minimum 0.02 0.02 0.14 0.02 

 Maximum 3.8 0.16 0.35 3.8 

 Mean 0.21 0.07 0.26 0.20 

 Selenium Minimum 0.05 0.18 1.5 0.05 

 Maximum 6.7 1.7 2.2 6.7 

 Mean 1.01 0.59 1.8 1.01 

 Uranium Minimum 0.08 0.01 1.4 0.01 

 Maximum 3.2 1.2 2.9 3.2 

 Mean 0.61 0.46 2.1 0.64 

30
FACTORS AFFECTING EXTRACTION OF COAL RESOURCES 

There are many factors that can affect the availability of coal for mining. The three general groups 

of factors or considerations in Powder River Basin coal development are: legal unsuitability criteria, 

land-use conflicts, and technological factors. Table 7 shows a listing of the factors under each of 

these groups. It is important to note that not every factor included in table 7 affects development 

within the Gillette coal field. 

Table 7. List of factors that can restrict coal mining 

Legal unsuitability criteria from Federal Coal Management Regulations 

(43 CFR 3461.5) 

Federal Land Systems

Rights of way and easements (railroad) 

Dwellings, roads, cemeteries, and public buildings

Wilderness study areas

Lands with outstanding scenic quality

Lands used for scientific study

Historic lands and sites

Natural areas

Critical habitat for threatened or endangered plant and animal species

State listed threatened or endangered species

Bald or golden eagle nests

Bald and golden eagle roost and concentration areas

Federal lands containing active falcon cliff nesting site 

Habitat for migratory bird species

Fish and wildlife habitat for resident species

Floodplains

Municipal watersheds

National resource waters

Alluvial valley floors 

State or Indian Tribe criteria 

Land-use conflicts 

Towns 

Pipeline 

Oil and gas development (a land-use restriction for surface mining) 

Gas plant 

Power lines

Gravel pits

Archaeological areas

Surface and coal ownership issues

Wetlands

31
Table 7 continued. 

Technological factors

Coal quality

Overburden geochemistry

Overburden thickness (coal too deep) 

Mined-out areas or limit of coal 

Surface subsidence over abandoned mines

Active mines 

Abandoned mines

Clinkered areas

Coal beds too close together 

Coal beds too thin (coal beds less than 2.5 ft thick were considered too thin to mine) 

Coal beds too thick (for underground mining) 

Coal bed discontinuities

Roof or floor problems 

Barrier pillars 

Oil and gas development (technological restriction for underground mining) 

Coalbed methane development 

The coal leasing unsuitability criteria are listed in the Code of Federal Regulations, Title 43 Subpart 

3461 (43 CFR 3461) (Office of the Federal Register, 2000). These 20 specific legal criteria are used 

to determine if an area can be mined by surface mining methods. The 43 CFR 3461 regulations are 

issued under the authority of, and implement several major provisions of, Public Law 95-87, which 

is part of the Surface Mining Control and Reclamation Act of 1977 (30 U.S.C. 1201 et seq.) (1977). 

The 20 unsuitability criteria involve consideration of scenic areas, natural and historic values, 

wildlife, flood plains, alluvial valley floors, and other special values (U.S. Bureau of Land 

Management, 1984). 

Restrictions to mining vary with location and local land-management regulations. Thus, different 

study areas can have different mining restrictions and availability considerations. This report reflects 

our assumptions concerning restrictions to mining, which are based on local practices in the Powder 

River Basin, and specifically to those practices within the Gillette coal field. In addition, the BLM 

in Casper, Wyoming, provided guidance concerning restrictions to mining and the distances to be 

buffered around specific features, as well as files delineating many of the features and the buffer 

distances around the features that we used for our study. Because required buffer distances can 

change from year to year, all of the distances that we used were conservative in that we selected 

buffer distances that were considered to be the maximum amount that might be required by future 

regulations. A more detailed determination of restrictions and other availability considerations would 

be necessary as part of leasing and mine-planning phases of property development. 

The following is a detailed discussion of the various restrictions to mining that we used for this 

investigation. Figure 20 shows the areas within the Gillette coal field where the restrictions were 

applied to limit the areas in which coal resources were calculated. 

CITIES: The municipalities of Gillette and Wright are located within the Gillette coal field and 

are permanent restrictions to mining. For this study, a 300-ft restriction buffer was placed around 

the city limits of Gillette and the town of Wright. 

32
ROADS: County roads (mostly gravel) cross many areas throughout the Gillette coal field. It is 

assumed that these roads could be fairly easily relocated to allow mining to proceed; therefore, 

these roads are not considered restrictions to mining. However, a number of State and U.S. 

highways, including an interstate highway, are also present within the study area. Although it is 

possible that some or all of these highways could also be relocated to allow for mining, we 

consider them to be restrictions to coal mining for assessment purposes. They are shown on 

figures 19 and 20 with a buffer; the State highways, including buffers on each side, are 220 ft 

wide. Interstate Highway 90, including its buffers on each side, is 270 ft across. 

33
RAILROADS: There are two main railroad lines within the Gillette coal field, as well as a 

number of spur lines that serve the existing coal mines. Because the spur lines can be expected 

to be moved as the mining operations proceed, these spur lines are not considered to represent 

restrictions to mining. It is conceivable that the main lines of the existing rail routes could also 

be relocated to allow mining to proceed, once the appropriate agreements and permits were 

acquired. However, for the purposes of this study, we have assumed that these main rail lines 

would not be moved, and we consider them, and the 300 ft buffer along each side of them, to be 

restrictions to coal mining. 

PIPELINES: There is a network of underground oil and gas pipelines throughout the Gillette coal 

field. Probably most, if not all, of these pipelines would be moved so that surface mining could 

proceed; however, moving and restoring them would represent an added economic consideration 

to mining. For this study, we have considered only the major pipelines to be restrictions to 

mining. The pipeline restrictions include a 100 ft buffer along each side of the pipelines. 

AIRPORT: About two miles north of Gillette lies the Campbell County airport. We believe it 

unlikely that this facility would be relocated to allow for surface mining on the land, so the airport 

grounds, along with a 300-ft-wide buffer, are determined to be a permanent restriction to mining. 

POWER PLANTS: Electrical power-generating facilities of the Wyodak Plant and the Neil 

Simpson Plant lie a few miles to the east of Gillette, near the coal outcrop boundary of the Gillette 

coal field. The area occupied by these installations, as well as a 100-ft buffer, are shown in 

figure19; this land is a permanent restriction for coal mining. 

HILIGHT GAS PLANT: The plant, located approximately 7 miles to the northeast of Wright, 

connects to several major pipelines for gas and crude oil, as well as to a pipeline for gasprocessing-plant products. This installation, with a 100-ft buffer, is considered a restriction to 

coal mining. 

OIL AND OIL-RELATED GAS WELLS: As of July 2000, there were more than 2,300 active 

producing wells within the Gillette coal field; these wells include those in the study area’s two 

major oil and gas fields – Hilight and Kitty. How land-use conflicts between coal mining and the 

oil and gas field development would be resolved will depend on economic conditions, regulations, 

and negotiations between oil developers and coal developers. Perhaps an area around a major 

cluster of active wells would be eliminated from mining activities until these wells are no longer 

actively producing. On the other hand, mining activities might proceed around individual active 

wells that are given a buffer zone. Conversely, specific wells might be plugged and then reestablished after mining. For this study, we have buffered around each active well (300-ft-buffer 

radius) and consider these areas as restrictions to mining. 

ALLUVIAL VALLEY FLOORS: All areas within the coal field identified as alluvial valley

floors by the Bureau of Land Management, where mining would interrupt, discontinue, or 

preclude farming, are unsuitable for surface coal mining, thus are deemed to be restrictions.

AREAS OF CLINKER: There are many areas along the coal outcrop, some areas as much as 

several miles down dip from the coal outcrop, where coal has burned in-place and produced 

overlying clinker. Because coal beneath areas containing clinker is either burned or compromised 

in quality, we considered these areas to be restrictions to mining. The eastern limit of the coal, for 

34
this study, was drawn so that most areas along the coal outcrop that contain clinker are excluded 

from consideration for resource assessment. 

The following detailed discussions address other potential mining restrictions that also need to be 

considered. Although not deemed by us to represent restrictions to mining in the study area, they

likely would represent limitations to mining within other areas. 

COALBED METHANE WELLS AND PIPELINES: The rapid growth in coalbed methane 

production within the Gillette coal field, particularly during the last five years, has resulted in the 

placement of thousands of wells, along with their accompanying pipeline infrastructure, 

throughout the study area. Designating all of these wells and their extensive gas delivery systems 

as being restrictive to mining, would effectively exclude most of the coal field from resource 

consideration. As stated previously in the section on other energy commodities in the Gillette 

coal field, the expected lifetime of a coalbed methane well producing from a single coal bed is 10 

to 12 years. For the purpose of this study, we have assumed that the coal within any part of the 

study area will be mined after the coalbed methane operations have ceased operating in that area. 

Therefore, we have not designated any coalbed methane facilities as representing a restriction to 

mining. 

FEDERAL LAND 

SYSTEMS: There are no 

Federal lands systems that 

are unsuitable for coal 

leasing in the Gillette coal 

field. The study area does 

contain a part of the Thunder 

Basin National Grassland, a 

large area in northeastern 

Wyoming that includes 

scattered Federal lands under 

the jurisdiction of the U.S. 

Forest Service, although it is 

not part of a National Forest. 

 The same unsuitability

criteria and land-use 

considerations discussed in 

this report apply to coal 

mining on the Thunder Basin 

National Grassland. Where 

the mineral ownership there 

is Federal, the BLM develops 

the coal-leasing and mining 

stipulations in conjunction 

and cooperation with the U.S. 

Forest Service. Federal 

surface management areas 

and Federal subsurface coal 

ownership are shown in 

figure 21. 

35
POWER LINES: The authors expect that all power lines within the study area could be fairly

easily moved to accommodate surface mining operations. Thus, power lines are not considered a 

restriction to mining in the area of the Gillette coal field. 

RIVERS, STREAMS, AND LAKES: The Belle Fourche River is the most significant body of 

flowing water within the Gillette coal field. However, throughout its course within the coal field, 

it is a shallow, slow moving, meandering stream, as is the case with all of the other larger creeks 

in the study area. Surface mining operations could temporarily relocate the courses of these 

streams and then return them to their pre-mining locations during mine reclamation. Only the 

parts of the watercourses that have been designated by the BLM as alluvial valley floors would 

need to be preserved with no modification. There are no major lakes present within the Gillette 

coal field; the shallow lakes and small ponds that do exist could either be temporarily moved 

during mining or simply reformed after the mining operations ceased. 

DWELLINGS AND BUILDINGS: Individual dwellings and buildings that exist within the 

Gillette coal field, outside of the incorporated areas of Gillette and Wright, are not considered to 

represent restrictions to mining. These individual structures could probably be purchased by a 

coal company, which could then move or destroy them in order to proceed with mining.

RAPTOR SITES: In the proposed final environmental impact statement for the Buffalo Resource 

Area (U.S. Bureau of Land Management, 1985), golden eagle sites (with one-mile buffers) were 

identified as unsuitable for mining. However, currently these and other raptor sites are considered 

open to leasing and coal mining, pending further study; the mining effects at the sites could 

probably be mitigated. Because raptor sites are not considered to be a permanent restriction to 

mining, they were not excluded in this study.

ARCHAEOLOGICAL AREAS: No major archaeological areas that would prevent mining are 

known in the study area. There are several minor archaeological sites and also several minor 

historic sites within the Gillette coal field. A mitigation plan would be developed before coal 

mining disturbed these areas; therefore, coal within these known sites was not excluded from this 

resource study. 

In some cases, an area that was originally declared unsuitable for coal mining could have a 

mitigation measure developed to the extent that would permit mining. Economic analyses by the 

coal developer would help to determine whether costs for mitigation would preclude mining. 

Coal quality was not considered to be a restriction when determining the economically recoverable 

coal resources. The quality of a coal can be a factor in its marketability because government 

regulations prevent the use of coal containing potentially hazardous environmental pollutants at 

coal-fired power plants. The regulatory standard for sulfur dioxide emissions from coal-fired power 

plants restricts the amount of SO2 per million Btu that can be released into the air to 1.2 pounds. In 

the Gillette coal field, the coal is relatively low in total sulfur content and almost all of the minable 

coal contains sulfur content and Btu values that equate to less than the standards set for SO2

emissions from power plants. 

36
STUDY METHODOLOGY 

Data Collection, Correlation, and Preparation

The methodology for calculating economically recoverable coal resources for assessed coal beds in 

the Gillette coal field involved several phases. The first phase involved the compilation and 

correlation of data and the delineation of coal-mining units and areas of restrictions, including: (1) 

acquisition of coal stratigraphic and analytical data, and their transfer into a point-data management 

system; (2) correlation and grouping of coal and parting into coal beds, or mining units; (3) 

transference of point-source, line, and polygon data to a geographic information system (GIS); and 

(4) conversion of point-source, line, and polygon data into vector coverages and/or raster grids using 

the GIS program. The second phase was to calculate the original coal resources, previously mined 

resources, restricted coal resources, and coal resources available for mining. The third phase was to 

calculate recoverable coal tonnages, determine a mine model for the study area, and finally, apply a 

cost model to the recoverable resource to determine how much of the resource could be produced at 

a profit. 

Our study involved compilation of three types of data. The first was point-source data consisting of 

stratigraphic and coal quality information. As noted earlier, in the section titled Coal Bed 

Correlations, we used stratigraphic interpretations and representative coal quality data from a USGS 

open-file report by Flores and others (1999). Point-source geologic data were initially processed 

using StratiFact software (GRG Corporation, 1996) to store, manipulate, and graphically display

cross sections throughout the study area. Where Kent and others (1980) or Pierce and others (1990) 

contained correlations of coal beds for the same drill holes used in this report we used their coal bed 

names as a basis for our correlations. We correlated individual coal beds and grouped the coal beds 

and partings into mining units using StratiFact visualization. Coal beds and partings were grouped 

into mining units by assigning coal bed designations to the appropriate lithologic units. Then, coalmining unit data were exported using StratiFact (GRG Corporation, 1996), and brought into 

ArcView (Environmental Systems Research Institute, 2001a). 

We devised a system of identifying and naming these coal intervals that would be modeled for 

mining. As previously noted, it was difficult to correlate individual coal beds across the whole study

area. Data for some drill holes indicated a thick coal bed with no partings, but data for nearby holes 

indicated the same coal with partings that separate the thick coal into several coal beds. If we had 

applied strictest coal-correlation conventions, each of those parts of the single thick coal might have 

a separate name. In that case we would have a mixture of small extents of multiple, thin coal beds 

and small extents of single, thick coal beds across the study area. Such a distribution would not be 

feasible for coal-extraction modeling. 

To avoid this problem, we grouped coal beds and partings together in intervals that were 

representative of the five coal beds being modeled. In each interval, we verified that total parting 

was less than 50 percent of the entire thickness; in most cases, total parting was much less than 50 

percent. By the use of this system, we could accommodate the variation in coal stratigraphy over our 

1,500-sq-mi-study area, and also accommodate differences in geophysical-log interpretation that 

may have existed in our original data set. The five coal intervals represented reasonable groupings 

of coal and partings in our view, hence were considered to be the mining units. 

The second data type that we used consisted of polygon or line data that delineated the surface 

extent of clinker and other areas that pose restrictions to mining, and areas of Federal, State and 

private coal ownership. The BLM provided many of these data in digital format. The digital line 

37
data was processed using one or more GIS computer programs. Some of the BLM data could be 

directly imported into ArcView for processing, whereas other data required prior manipulation with 

ArcInfo (Environmental Systems Research Institute, 2001b) before importation into ArcView. 

The third type of data was the digital elevation model (DEM), which is a digital file produced by the 

National Mapping Division of the USGS that represents the surface topography as a grid, or raster 

file. The DEM is used to calculate overburden thickness by subtracting the raster values of the 

elevation of the top of the Upper Wyodak coal bed from the DEM surface-elevation raster values. 

Figure 15 shows overburden thickness above the Upper Wyodak coal, which is the thickest and most 

pervasive coal bed assessed for this study. The overburden thickness for the Wyodak coal bed was 

used in combination with the parting thicknesses to calculate stripping ratio of rock (overburden plus 

parting thickness) to total coal (total coal thickness of all five assessed beds). The calculation and 

application of the stripping ratios is discussed in more detail in the next section of this report. 

Coal Resource Calculation 

The point, line, and raster data, which included information on the coal-mining units, areas restricted 

from mining, coal ownership, and overburden, were combined in ArcView. ArcView’s program

extension, Spatial Analyst, was used to create raster grids of the thickness of each of the coal-mining 

units and to delineate the area in which the mining units could be modeled for each type of resource 

category. Areas in which coal mining would be restricted were also converted to raster data. 

Resource categories were discussed earlier in this report, but the following discussion explains how 

the restrictions were applied in ArcView using the Spatial Analyst extension. Resource tonnages 

were derived by first calculating the volume of each mining unit and coal ownership category in 

acre-ft. This volume was then multiplied by a conversion factor for subbituminous coal of 1,770 

short tons per acre-ft. Original resources were calculated for each of the coal-mining units for each 

of the coal ownership categories with no limitations or restrictions applied. Remaining resources

were calculated for each mining unit and coal ownership category, using the volume of original 

resources minus the volume of coal that had been previously mined. The volume of coal plus 

partings in areas that would be restricted from mining (the unavailable resources) were then 

calculated for each of the mining units and coal ownership categories and those volumes were 

subtracted from the remaining resources to determine the available resources. Table 8 shows the 

results of coal resource calculations for the original, previously mined, remaining, restricted 

(unavailable), and available coal tonnages, reported by coal-mining unit and coal ownership 

categories. 

As the next step, we developed preliminary extraction scenarios (mine models) that would be used 

in COALVAL (Plis and others, 1993; Suffredini and others, 1994) to determine the resources in 

each coal-mining unit. The recoverable resource is the available resource minus the amount of 

coal that would be lost through various mining methods. We used a mining loss of 10 percent for 

coal-mining units in the Gillette coal field (table 8). This is the standard amount of coal loss that is 

applied in the COALVAL for a truck and shovel mining operation. The recoverable resources 

include coal plus parting material. 

38
Table 8. Original coal resources, previously mined resources, unavailable resources, available resources, mining losses, and recoverable resources o

the Gillette coal field, reported in millions of short tons and by coal ownership category. These resource tonnages include coal plus parting material. 

of independent rounding. 

Coal 

unit 

Coal 

ownership 

Original 

resources 

Percent that is 

parting material 

Previously 

mined 

resources 

Remaining 

resources 

Unavailable 

resources2

Available 

resources 

Mining losses 

on available 

resources 

Recove

resou

Federal 7,484.3 2.4 15.2 7,469.1 406.2 7,062.9 706.3 6State 377.4 2.6 .2 377.2 26.1 351.1 35.1 Private 184.2 7.4 4.0 180.2 33.3 146.9 14.7 

Wyodakrider 

Total 8,045.9 2.5 19.4 8,026.5 465.5 7,561.0 756.1 6

Federal 94,859.7 6.0 3,765.5 91,094.2 7,142.1 83,952.1 8,395.2 75State 5,294.1 6.5 204.9 5,089.2 487.7 4,601.5 460.2 4Private 2,305.4 6.8 186.5 2,118.9 440.0 1,678.9 167.9 1

Upper Wyodak

Total 102,459.2 6.0 4,156.9 98,302.3 8,069.7 90,232.6 9,023.3 81

Federal 873.2 1.2 0 873.2 161.6 711.6 71.2 State 13.1 0.2 0 13.1 4.9 8.2 .8 Private 15.4 0 0 15.4 3.2 12.2 1.2 

Canyon 

Total 901.6 1.1 0 901.6 169.7 731.9 73.2 

Federal 20,637.7 11.2 137.7 20,500.0 1,526.9 18,973.1 1,897.3 17State 1,038.8 11.4 4.1 1,034.7 82.7 952.0 95.2 Private 577.7 12.5 .9 576.8 119.1 457.7 45.8 

Lower Wyodak/ Werner 

Total 22,254.2 11.2 142.7 22,111.5 1,728.6 20,382.9 2,038.3 18

Federal 2,312.5 12.9 0 2,312.5 96.7 2,215.8 221.6 1State 136.0 12.6 0 136.0 5.9 130.1 13.0 Private 34.5 15.8 0 34.5 .9 33.6 3.4 

Gates/ Kennedy

Total 2,483.0 12.9 0 2,483.0 103.5 2,379.5 238.0 2

Federal 126,167.5 6.7 3,918.4 122,249.1 9,333.4 112,915.7 11,291.6 101State 6,859.4 7.1 209.2 6,650.2 607.3 6,042.9 604.3 5Private 3,117.1 8.0 191.4 2,925.7 596.5 2,329.2 232.9 2

All assessedcoal beds

Grand total 136,143.9 6.8 4,319.0 131,825.0 10,537.2 121,287.8 12,128.8 109

2 Mining restricted by municipalities, State and Federal highways, railroad main lines, major oil and gas pipelines, an airport, power plants, the Hilight 

oil-related gas wells, alluvial valley floors, and clinkered areas.
COALVAL is a coal property-evaluation software package developed by the U.S. Bureau of Mines. We 

used this software because it could efficiently handle the large quantity of cost data associated with our 

study. COALVAL has the capability to evaluate as many as 25 coal seams, each to be mined with as 

many as seven different mining methods. The software package produces summary spreadsheets that list 

the cost per clean ton of coal to mine the resources (“free on board” or f.o.b. cost at load-out) for each 

property, seam, and mining method. COALVAL performs discounted cash flow-rate of return (DCFROR) analyses. The DCF-ROR is defined as the rate of return that makes the present worth of future 

generated cash flow over the life of a project equal to the present worth of all after-tax investments 

(Barnes, 1980, p. 137). For this study we updated the DCF-ROR using year 2001 cost indices to calculate 

the costs of coal production. 

Mining cost models include assumptions on recovery factors and production costs for specific mining 

methods. For this investigation of assessed coal in the Gillette coal field, we assumed that all mining, for 

the foreseeable future, would be limited to surface methods using truck and shovel operations. 

Furthermore, we assumed that this mining would be restricted to the five coal-mining units discussed 

earlier. Mining costs were based on the application of mining equipment and personnel assumptions for 

a super large mining operation. 

40

Economic coal resource

analysis was performed on the 

basis of “waste rock-to-coal 

ratio” for all coal-mining units 

combined (fig. 22). The wasteto-rock-ratio is calculated using 

the total thickness of all rock 

material (including overburden, 

interburden, and partings) and 

the total thickness of all coal at 

a given location. The stripping 

ratio is only used in this study

to calculate economic coal 

resources. The same stripping 

ratio is applied to all of the 

assessed coal beds, because it is 

assumed that when mining 

proceeds, all five coal beds will 

be mined. The stripping ratio 

was gridded using the lateral 

extent of each coal assessment 

unit as a grid boundary, to 

reflect the abrupt change in coal 

thickness that would occur with 

more or fewer coal beds being 

mined. The cost to produce coal 

is directly related to the amount 

of rock material that must be 

moved in mining, and the 

relation between the amount of 

rock material to be moved and 

the amount of coal that will be 

produced. Using the stripping 

ratio, instead of determining the 
resources only on the basis of coal-bed thickness, allowed us to directly correlate mining costs to the 

amount of rock material that would have to be removed to mine the coal beds. The stripping ratio is one 

of several variables that were used to determine the cost of coal production. Table 9 shows the economic 

coal resources for each of the assessed coal beds reported by stripping ratio. 

Table 9. Recoverable resources of assessed coal-mining units in the Gillette coal field reported by stripping ratio (waste rock to 

coal). Resources are reported in millions of short tons and include coal plus parting material. 

Coal-mining unit Recoverable resources in millions of short tons reported by stripping ratio 

< 1:1 >1:1- 2:1 >2:1- 3:1 >3:1- 4:1 >4:1- 5:1 >5:1- 6:1 All stripping 

ratios 

Wyodak rider 31 86 272 650 1,066 1,652 6,804

Upper Wyodak 1,419 5,529 11,148 18,239 26,056 35,215 81,210

Canyon 0 0 2 25 86 177 659

Lower 

Wyodak/Werner 279 1,389 2,696 4,165 5,637 7,442 18,345

Gates/Kennedy 0 0 0 0 9 107 2,141

All mining units 1,729 7,004 14,118 23,079 32,854 44,593 109,159

Tonnage of economically recoverable coal will necessarily vary with changes in coal prices and 

production costs. Cost factors for determining economically recoverable resources from recoverable 

resource estimates are described by Rohrbacher and others (1993), Suffredini and others (1994), Doney

(2000), and Western Mine Engineering (2000). COALVAL uses specific mining scenarios to determine 

coal production costs; the software calculates the operating costs associated with mining, using a specific 

mine model. The program then calculates the amount of coal in each bed that is available for different 

production cost ranges. 

For the purpose of this report we determined that a coal resource was economic for development if the 

cost of coal production was less than or equal to the current market value (sales price on a per-ton basis, 

free-on-board (f.o.b.) cost at load-out). Therefore, the amount of coal that is economic at a production 

cost of $3.00 would have a sales price of $3.00 or more. In our study, we calculated economically

recoverable resources for the following sales price levels: $3.00 per ton, $4.00 per ton, $5.00 per ton, 

$6.00 per ton, and $7.00 per ton. All tonnages of economic coal resources are reported for coal only. No 

parting material is included in the economic coal resources. 

The over-the-counter assessment for Powder River Basin coal at the mine load-out (f.o.b. cost) for 

February 2002 was $5.35 per ton for coal with a calorific value of 8,400 Btu and total sulfur content of 

less than 0.35 percent and $6.20 per ton for coal with a heat value of 8,800 Btu and a total sulfur content 

of less than 0.35 percent (McGraw Hill, Co., 2002). The mean calorific value of all assessed coal in this 

study, based on our coal quality data set, is 8,554 Btu with mean total sulfur content of 0.46 percent. 

Because the economic coal resources we report do not include parting material, which would lower Btu 

and increase total sulfur content, we considered current market value for the economic coal resources to 

be about $6.00 per ton. Table 10 shows the results of the economic coal resource calculations. 

It is important to note that in the Gillette coal field, the majority of the land surface is privately owned and 

the majority of the coal is federally owned (fig. 21). The ownership of the coal is an important aspect of 

coal resources in the coal field, as the BLM permits leasing for development of federally owned coal. 

The development of Federal coal in Wyoming contributed over $107,000,000 in royalties to the state in 

the year 2000 (U.S. Minerals Management Service, 2001). Knowledge of the volume of Federal coal is 

41
also important in determining National energy policy and in making land-use decisions. We believe that 

it is important to know the volume of Federal coal resources, as well as the resources that are owned by

State and private interests. Consequently, we calculated coal resources for Federal, State, and private coal 

ownership and these results are shown on tables 8 and 10. 

Table 10. Economically recoverable coal resources of all assessed coal (no parting material included) in the Gillette coal field, 

Powder River Basin, Wyoming. For the purpose of this report, coal is considered to be economic if the cost of production is less 

than or equal to the sales price. February 2002 over-the-counter assessment (projected sales price) for coal from the Powder 

River Basin was between $5.35 and $6.20 per ton (McGraw Hill Co., 2002). All tonnage values are reported in millions of short 

tons.

Coal 

ownership 

Economically 

recoverable 

resources at 

$3.00 

per ton 

sales price 

Percent 

of 

original 

resource 

Economically 

recoverable 

resources at 

$4.00 

per ton 

sales price

Percent 

of 

original 

resource 

Economically 

recoverable 

resources at 

$5.00 

per ton 

sales price 

Percent 

of 

original 

resource 

Economically 

recoverable 

resources at 

$6.00 

per ton 

sales price 

Percent 

of 

original 

resource 

Economically 

recoverable 

resources at 

$7.00 

per ton 

sales price

Percent 

of 

 original 

resource 

Federal 1,526 1.2 6,462 5.1 13,089 10.4 21,273 16.9 41,471 32.9

State 132 1.9 418 6.1 794 11.6 1,341 19.6 2,318 33.8

Private 71 2.3 123 3.9 235 7.5 465 14.9 807 25.9

Grand total 1,729 1.3 7,003 5.1 14,118 10.4 23,079 17.0 44,596 32.8

RESULTS 

The five coal units that we studied in the Gillette coal field (Wyodak rider, Upper Wyodak, Canyon, Lower 

Wyodak/Werner, and Gates/Kennedy) contain slightly more than 136.1 bst of total original coal resources. 

The percentage of each of the coal units that make up the total original coal resource in the Gillette coal 

field is shown on figure 23. About 89 percent, or nearly 121.3 billion tons of the original coal resource 

within these coal units, are considered available for development in the Gillette coal field (fig. 24). 

If these 121.3 billion available tons were to be completely developed for mining, approximately 12.1 

billion tons of coal could be expected to be lost in the mining process, resulting in an extractable resource 

of 109.2 billion tons (80 percent of original in-place resource). Because we assumed that the mined coal 

would not need washing, there would 

be no processing losses. Thus, this 

extractable resource is also the 

recoverable resource. Table 8 

summarizes the original resources, 

previously mined resources, 

unavailable resources, available 

resources, mining losses, and 

recoverable resources for the study

area. It should be noted that the 

original, available, and recoverable 

resource tonnages include about 9 bst 

of parting material, which are not 

included in the economic coal 

resource tonnage. 

42
The recoverable resources were then evaluated with cost models to determine the amount of 

economically recoverable resources for different stripping ratios (table 9) and at five sales-price levels 

(table 10). Our modeling 

determined that only coal 

resources with a rock-to-coal 

ratio of 4:1 or less (equivalent 

to a production cost of $5.79 or 

less per ton) are currently

economically recoverable. 

This category of economically

recoverable coal represents 17 

percent (23.1 billion tons) of 

the original resource, as shown 

graphically in figures 24 and 

25. A rock-to-coal ratio of 3:1 

or less resulted in a production 

cost of $4.68 or less per ton and 

represents about 10 percent 

(14.1 billion tons) of the 

original resource as economically recoverable. The amount of economically recoverable coal is 

significantly smaller at a rock-to-coal ratio of 2:1 or less (equivalent to a production cost of $3.53 or less 

per ton) and represents only about 5 percent (7.0 billion tons) of the original resource. For a rock-to-coal 

ratio of 1:1 or less (equivalent to a production cost of $2.70 or less), the amount of economically

recoverable coal is estimated to be just over 1 percent (1.7 billion tons) of the original resource. 

Although coal resources with a 

rock-to-coal ratio in excess of 4:1 

are not presently economically

recoverable, significant amounts of 

additional coal could become

profitable in the future if the sales 

price for the coal increased by just 

$1.00 per ton. For instance, at a 

rock-to-coal ratio of 6:1 or less 

(equivalent to a production cost of 

$6.91 or less per ton), 44.6 bst (33 

percent) of the original coal 

resource would be economically

recoverable. 

Table 10 also shows the amount of 

economically recoverable Federal, 

State, and private coal at various 

coal sales-price levels. At a production cost of $6.00 or less per ton (sales price of $6.00), for example, 

17 percent (21.3 bst) of the Federal coal, 20 percent (1.3 bst) of the State coal, and 15 percent (0.5 bst) of 

the private coal within the coal field are economically recoverable. 

43
CONCLUSIONS 

Results of the economic assessment of extractable coal resources in the Gillette coal field, Wyoming, 

indicate that there is a total of 136 billion standard tons of original coal resources for the five coal units 

assessed (fig. 25). Of these original coal resources, 89 percent (121 bst) of the coal resource is available 

and 80 percent (109 bst) is recoverable. Most importantly, only 17 percent (23 bst) of the original coal 

resource is economically recoverable at a sales price of $6.00 a ton. This amount of economic resource 

would change, depending on changes in current market prices, as shown in table 9. 

There are several reasons for the relatively high percentage of available, recoverable, and economically

recoverable coal within the Gillette coal field. There are few land-use and technological restrictions—

mining in the Gillette coal field occurs in areas that are largely undeveloped and contain few population 

centers. The area is suited for surface mining because topography is relatively flat, and there are 

numerous thick, gently dipping, relatively shallow coal beds. The use of large-scale, efficient, surfacemining methods contributes to the significant amount of recoverable and economically recoverable coal. 

A network of railroad lines already exists to transport coal from the mines. 

Several other studies of extractable coal by the U.S. Geological Survey have estimated original, 

recoverable, and economic coal resources for various areas. Results of recent studies for the Northern 

Wasatch Plateau coal field of Utah, the Somerset coal field of Colorado, the Bisti coal field of New 

Mexico (DST and Associates, 2002, personal communication) and the Hilight 7.5-minute quadrangle, 

which is within the Gillette coal field (Molnia and others, 1999; Osmonson and others, 2000), are shown 

in figure 26. The Hilight 7.5-minute quadrangle (fig. 4) encompasses about 52 sq mi within the southern 

part of the Gillette coal field. 

This study covers the same area as the study by Ellis and others (1999), but a larger stratigraphic interval. 

Ellis and others (1999) reported a total of 110 bst of coal in the Wyodak-Anderson coal zone within the 

Gillette coal field, whereas the available resource tonnage (121 bst) in our study includes two additional 

coal beds and parting material. The available resource tonnage decreases to 112 bst if we exclude the 

parting material, to more closely match the criteria used by Ellis and others (1999). Our estimate would 

be even lower had we excluded all coal that is under lease, as did Ellis and others (1999). 

44
Calculations of original and available coal resources add to the general body of knowledge regarding 

possible energy sources; however, these large coal resource estimates can be misleading. As shown in 

this report, the coal resource that is economically extractable is significantly less than the original or 

available coal resources. Additionally, this difference varies from one study area to the next. It is 

important to consider specific factors that can limit the amount of coal that could be produced within each 

study area. The calculation of economically extractable coal resources from coal units within specified 

areas, for different market values, provides useful data to developers and planners to determine the life of 

energy resources and to make informed land-use decisions. 

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