Quality of Economically Extractable Coal 

Beds in the Gillette Coal Field as Compared 

With Other Tertiary Coal Beds in the Powder

River Basin, Wyoming and Montana

By Margaret S. Ellis 

U.S. Geological Survey Open-File Report 02-174 

2002 

U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

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.......................................................................................................................................................... 3 

Introduction ................................................................................................................................................... 3 

Area and Geology of the Powder River Basin and Gillette Coal Field...................................................... 5 

Wyoming Coal Characteristics and Coal Quality........................................................................................ 8 

Wyodak-Anderson Coal Characteristics and Coal Quality in the Powder River Basin, Wyoming 

and Montana.................................................................................................................................... 9 

Characteristics and Quality of Wyodak-Anderson and Other Coal in the Gillette Coal Field, 

Wyoming....................................................................................................................................... 11 

Quality of Economically Extractable Coal Beds Assessed in the Gillette Coal Field Study .................. 14 

Conclusion................................................................................................................................................... 17 

References Cited ......................................................................................................................................... 18 

Figures

Figure 1. Map of the Powder River Basin, Wyoming and Montana, showing the basin axis, 

counties, major cities, and Gillette coal field................................................................................. 3

Figure 2. Location of mines in the Gillette coal field................................................................................. 4 

Figure 3. Map showing generalized geology in the part of the Powder River Basin around the 

Gillette coal field ........................................................................................................................... 5 

Figure 4. Map showing the location of stratigraphic cross sections through the northern, middle, 

and southern parts of the Gillette coal field ................................................................................... 6

Figure 5. West to east structural cross section through the northern part of the Gillette coal field ......... 7 

Figure 6. West to east structural cross section through the middle part of the Gillette coal field............ 7 

Figure 7. West to east structural cross section through the southern part of the Gillette coal field ......... 8 

Figure 8. Map showing locations in the Gillette coal field where samples from the WyodakAnderson coal zone were collected for coal quality analyses..................................................... 11 

Tables

Table 1. Summary of the apparent rank and calorific value of mined coal from coal fields in 

Wyoming......................................................................................................................................... 9 

Table 2. Designation of low, medium and high categories for total sulfur content and ash yield 

in coal, as defined in Wood and others, 1983................................................................................ 9 

Table 3. Coal quality summary data for Wyodak-Anderson coal in the Powder River Basin, 

Wyoming and Montana ................................................................................................................ 10 

Table 4. Coal quality summary data using weighted averages, one value for each parameter at 

each data point location, for Wyodak-Anderson coal in the Gillette coal field ......................... 11 

Table 5. Proximate, ultimate and calorific values using all sample analyses, more than one 

sample at each data point location, from coal beds in the Wyodak-Anderson coal zone in 

the Gillette coal field..................................................................................................................... 12 

Table 6. Trace element content of coal samples from beds in the Wyodak-Anderson coal zone in 

the Gillette coal field..................................................................................................................... 12 

Table 7. Summary of coal quality and production of coal from mines in the Gillette coal field 

supplied to coal-fired power plants in 1999................................................................................. 13 

Table 8. Proximate and ultimate analyses and calorific values of economically extractable coal 

in the Gillette coal field................................................................................................................. 15 

2 
Table 9. Values for potentially hazardous air pollutant trace elements in economically

extractable coal in the Gillette coal field...................................................................................... 16 

Table 10. Comparison of coal quality of the Wyodak-Anderson coal in the Powder River Basin 

and in the Gillette coalfield (Flores and others, 1999; Ellis and others, 1999), and of the 

economically extractable coal beds and the Upper Wyodak coal bed in the Gillette coal 

field ................................................................................................................................................ 17 

3 
ABSTRACT

The Powder River Basin, and specifically the Gillette coal field, contains large quantities of 

economically extractable coal resources. These coal resources have low total sulfur content and 

ash yield, and most of the resources are subbituminous in rank. A recent U.S Geological Survey

study of economically extractable coal in the Gillette coal field focused on five coal beds, the 

Wyodak rider, Upper Wyodak, Canyon, Lower Wyodak-Werner, and Gates/Kennedy. This report 

compares the coal quality of these economically extractable coal beds to coal in the WyodakAnderson coal zone in the Powder River Basin and in the Gillette coal field (Flores and others, 

1999) and other produced coal in the Gillette coal field (Glass, 2000). The Upper Wyodak, 

Canyon, and Lower Wyodak/Werner beds are within the Wyodak-Anderson coal zone. Compared 

with all coal in the Wyodak-Anderson coal zone, both throughout the Powder River Basin and just 

within the Gillette coal field; the thick, persistent Upper Wyodak coal bed in the Gillette coal field 

has higher mean gross calorific value (8,569 Btu/lb), lower mean ash yield (5.8 percent), and 

lower mean total sulfur content (0.46 percent). 

INTRODUCTION 

The U.S. Geological Survey (USGS) has recently conducted a study of economically extractable 

coal in the Gillette coal field, in the Wyoming part of the Powder River Basin (fig. 1). The study, 

concentrates on those coal beds that are most likely to be mined given such considerations as coal 

quality, coal thickness, s

the economics of 

mining, transport, a

current market value. 

Detailed information o

other recent USGS 

studies, which used 

similar criteria for 

determining 

economically

extractable coal in 

selected study

can be found in

publications by Mo

and others, 1997, and

Osmonson and o

2000. A major factor in

determining coal 

development potential 

is coal quality, because 

if the coal has hig

sulfur content, high ash

yield, or certain trace 

element content, it m

require cleaning and/ or 

processing before it 

could be utilized, which

may make the coal 

tripping ratio, land use, environmental and technologic restrictions, and 

nd

n

 areas, 

lnia

thers,

h

ay

4 
uneconomic for development. 

Most coal currently being mined is used for electric power generation. Each coal-fired power 

plant is designed to work with coal beds that have specific ranges in calorific values [British 

thermal units (Btu)], concentrations of sulfur, and ash yield. Coal that does not fit the 

requirements of the power plant, because it has high sulfur content, must be cleaned or blended 

with other coal to meet power plant specifications for utilization. Additionally, the U.S. Clean 

Air Act Amendment (U.S. Environmental Protection Agency, 1996) has set new Federal 

regulations on sulfur dioxide emissions. Current standards limit flue-gas emissions from coalfired power plants to no more than 1.24 pounds of sulfur dioxide per million Btu (lb 

SO2/mmBtu). The lb SO2/mmBtu is a calculated value using the sulfur content of the coal (in 

percent) and the calorific value (in Btu) of the coal. The quality of coal, especially the sulfur 

content, is therefore a very important factor in determining what coal is economic for 

development. 

The gross calorific value of Tertiary coal in the Powder River Basin, and specifically of the coal 

beds studied by the U.S. Geological Survey (USGS) in the Gillette coal field, is relatively low 

compared with the gross calorific value of coal from most other parts of the United States. 

Although the Gillette coal has relatively low calorific value, it has much lower sulfur content and 

lower ash yield than coal from most other parts of the country. Many power plants can use coal 

with lower gross calorific values; therefore the Gillette coal is in high demand because it does not 

require cleaning and it can be utilized either exclusively or be blended with other coal to meet 

utilization specifications. Mines located within the Gillette study area (fig. 2) produced about 305 

million short tons of coal, or about one third of the total national production, in 1999 (Resource 

Data International, Inc., 

2000). 

The comparison of coal 

quality, which follows a 

general discussion of 

geology in the Powder River 

Basin (fig. 1), is organized 

with the discussion 

progressing from a regional 

overview to a detailed 

picture of the economically

extractable coal beds r

studied in the Gillette c

field. Coal quality data is

compiled from a variety of 

sources and consists of da

on Wyoming coal, WyodakAnderson coal in the Powder 

River Basin, WyodakAnderson coal in the Gillett

coal field, produced co

from mines in the Gillette 

coal field (fig. 2), and the 

five coal beds from the 

USGS study in the Gille

coal field. 

ecently

oal

ta

e

al

tte

5 
AREA AND GEOLOGY OF THE POWDER RIVER BASIN AND GILLETTE COAL 

FIELD 

Minable coal discussed in this study is within the Tongue River Member of the Fort Union 

Formation in the Powder River Basin of Wyoming and Montana (fig. 3). The Powder River 

Basin is an asymmetrical structural basin with an axis that trends northwest-southeast (fig. 1) on 

the western side of the basin. The basin was formed during Late Laramide time by uplift of 

surrounding areas (including the Bighorn uplift to the west; the Casper arch, Laramie Range, and 

Hartville uplift to the south; and the Black Hills uplift to the east) and subsequent subsidence 

within the basin area (Curry, 1971; Perry and Flores, 1994). 

The basin, as defined by this study, is delineated by the contact between the Tertiary Fort Union 

Formation and the Late Cretaceous Hell Creek, Fox Hills, and Lance Formations, and Pierre 

Shale, on the northwest, west, south and east sides of the basin. In the north and northeast the 

basin boundary is defined by the course of the Yellowstone River. The Powder River Basin 

covers more than 22,000 sq mi (56,980 sq km) in Wyoming and Montana. 

The Fort Union Formation is more than 5,200 ft (1,585 m) thick in the deepest part of the basin. 

This formation is overlain by exposures of the Eocene Wasatch Formation, in the central part of 

6 
the basin. Fort Union rocks dip an average of 20 to 25 degrees to the east along the western 

margin of the basin, and dip an average of 2 to 5 degrees to the west along the eastern margin of 

the basin. The formation consists of sandstone, shale, mudstone, and coal, and is divided into 

(from top to base) the Tongue River, Lebo Shale, and Tullock Members, based primarily on 

lithology, thickness, and color. The variations in Fort Union Formation rock types and 

characteristics are controlled by source material, environments of deposition, and influences on 

the sediment subsequent to deposition. 

 

Fort Union coal in the Powder River Basin developed from peat accumulations in mires located 

adjacent to fluvial drainages. Most of the coal formed in thick, discontinuous, pod-like peat mires 

that were split continually by converging and diverging fluvial channels (Flores, 1986; Fort 

Union Coal Assessment Team, 1999). This resulted in a complex relationship of coal beds, 

indicated by the merging, splitting, and pinching-out of the beds over short distances. 

The Gillette coal field is on the eastern 

edge of the Powder River Basin, 

Wyoming (fig. 1). The coal field 

boundary used for this study is very

similar to the Gillette coal field area that 

was defined by USGS geologists in the 

past (Keefer and Schmidt, 1973; Denson 

and Keefer, 1974; Fort Union Coal 

Assessment Team, 1999) and was 

selected to include areas of active mines 

and adjacent areas where there is a 

potential for future coal development. 

The eastern boundary of the coal field is 

delineated by the outcrop of WyodakAnderson coal; mapped extent of 

Wyodak-Anderson clinker; or where that 

data is not present, the contact of the 

Wasatch Formation and the Fort Union 

Formation (Heffern and others, 1993; 

Heffern and Coates, 1997; Boyd and Ver 

Ploeg, 1997; Kent and others, 1980; and 

Coates and Heffern, 2000). The n

boundary is between T. 53 N. and T. 52

N. This boundary is about 5 mi (8 km) 

north of the Buckskin Mine (fig. 2). Th

southern boundary is between T. 40

and T. 39 N. The southernmost mine

included in the coal field is the Antelope

Mine (fig. 2). The western edge of the 

coal field is between R. 74 W. and R. 73 

W. The western boundary is about 10 mi (16 km) from the westernmost mine in the Gillette c

field. The coal field encompasses about 1,500 sq mi (3,885 sq km). 

orthern

e

N.

oal

The Gillette coal field can be divided into northern, middle, and southern parts. West-to-east 

trending cross-sections, the locations of which are shown in figure 4, show examples of the lateral 

variations of Tertiary coal in the Gillette coal field (figs. 5, 6, and 7). On all three cross sections 

the coal beds split to the west and merge into one or more thick beds to the east. In the northern 

7 
part of the coal field the 

correlation of coal beds is 

particularly difficult 

because there are many

splits in the coal and beds 

are discontinuous where 

peat in the original coal 

swamp was eroded by

contemporaneous fluvial 

channels. Coal beds in 

the middle and southern 

parts of the coal field are 

much more laterally

continuous. 

8 
WYOMING COAL CHARACTERISTICS AND COAL QUALITY 

Coal in Wyoming typically ranges in apparent rank from subbituminous to high-volatile A 

bituminous. The subbituminous coal is Tertiary or Cretaceous in age and occurs in almost all of 

the coal basins. Almost all bituminous coal is Cretaceous in age, although some deeply buried 

late Paleocene coal is also bituminous. Generally, older coal beds are higher in apparent rank, but 

high coal rank is more a factor of depth of burial (greater degree of metamorphism of the peat due 

to higher geothermal gradient and overlying pressure) than of age. The apparent rank of coal is 

classified based on its calorific value on a moist, mineral-matter free Btu (mmmfBtu) basis,

percent of fixed carbon and volatile matter on a dry, mineral-matter-free basis, and its 

agglomerating characteristics (Wood and others, 1983, table 1). According to Wood and others 

(1983) subbituminous coal ranges from 8,300 to 11,500 mmmfBtu and is non-agglomerating, and 

bituminous coal ranges from 10,500 to 14,000 mmmfBtu and is commonly agglomerating. The 

gross calorific values (Btu) of coal produced from various coal fields in Wyoming are shown in 

Table 1. According to Glass (2000) coal being mined in the Powder River Basin ranges from

about 7,420 to 10,410 Btu and is subbituminous in apparent rank. 

Higher rank bituminous coal in Wyoming generally has moisture content less than 15 percent, 

volatile matter content between 30 and 40 percent, and fixed carbon content greater than 40 

percent. The lower rank subbituminous coal has moisture content between 20 and 30 percent and 

volatile matter and fixed carbon content of about 30 percent (Glass, 2000). 

Ash yield and sulfur content in coal is related to the depositional environment in which the peat 

accumulated and the volume and type of sediment deposited in the peat. According to Wood and 

9 
others (1983), sulfur content and ash yield can be divided into high, medium, and low categories. 

The values for these categories are shown in table 2. Ash yield and sulfur content of the 

Paleocene coal mined from the Powder River Basin tends to be low, but ash yield and sulfur 

content for coal of all ages and throughout the state of Wyoming varies greatly. Sulfur content, 

ash yield, and trace element content in Cretaceous coal is generally higher than that found in 

Tertiary coal. These higher values in Cretaceous coal are probably caused by the influx of marine 

sediment into Cretaceous peat swamps (Flores and others, 1994). In low sulfur coal the form of 

sulfur is primarily organic, whereas is the high sulfur coal it is mainly pyritic. Much of the pyritic 

sulfur can be removed from coal mechanically through cleaning processes. 

Table 1. Summary of the apparent rank and calorific value of mined coal from coal fields in Wyoming. Btu 

is British thermal units. Modified from Glass (2000) 

Coal field Apparent coal rank 

Range of gross 

calorific value 

(Btu/lb) 

Mean of gross 

calorific value 

(Btu/lb) 

Powder River-NW Subbituminous 9,000-10,410 9,410 

Powder River-East Subbituminous 7,420-9,600 8,580 

Powder River- South Subbituminous 7,610-8,870 7,710 

Hanna Subbituminous and bituminous 8,310-12,600 11,030 

Green River Subbituminous 9,290-10,000 9,480 

Hams Fork Subbituminous 9,270-10,000 9,570 

Bighorn Bituminous 10,730-11,246 10,970

Table 2. Designation of low, medium, and high categories for total sulfur content and ash yield in coal, as 

defined in Wood and others, 1983 

Coal quality 

parameter 

Low Medium High 

Total sulfur (percent) Less than 1 1 to 3 Greater than 3 

Ash yield (percent) Less than 8 8 to 15 Greater than 15 

WYODAK-ANDERSON COAL CHARACTERISTICS AND COAL QUALITY IN THE 

POWDER RIVER BASIN, WYOMING AND MONTANA 

Coal included in this study in the Gillette coal field, Wyoming is primarily within the WyodakAnderson coal zone that was defined by the Fort Union Assessment Team (1999) in their study of 

coal in the Powder River Basin of Wyoming and Montana. According to their data, the WyodakAnderson coal zone in the Powder River Basin has a maximum net coal thickness, defined as the 

summed thickness of all coal beds greater than 2.5 ft (0.76 m) thick, of 284 ft (86.6 m). The 

entire zone is more than 600 ft (183 m) thick, measured from the top of the uppermost coal to the 

base of the lowermost coal, in the central part of the basin. The zone contains up to six coal beds 

10 
in a given location. Coal beds average 25 ft (7.6 m) in thickness, and are separated by clastic 

sedimentary rocks ranging from a few feet to 150 ft (45.7 m) in thickness. 

Wyodak-Anderson coal is generally considered to be clean, and compliant with SO2 emissions 

standards (U.S. Environmental Protection Agency, 1996. Arithmetic mean values of the 

Wyodak-Anderson coal from samples collected from 300 locations throughout the Powder River 

Basin indicate that the coal contains low percentages of total sulfur and has a low ash yield (table 

3). 

Table 3. Coal quality summary data for Wyodak-Anderson coal in the Powder River Basin, Wyoming and 

Montana. The table was modified from Stricker and Ellis (1999). Proximate and ultimate analyses are 

reported on an as-received basis. Trace elements are reported in parts per million and are reported on a 

whole-coal and remnant-moisture basis. L indicates that the value was below the detection limit for the 

measuring device 

Coal quality Range 

parameter 

Number of 

samples Minimum Maximum 

Mean 

Moisture (percent) 300 14.50 42.30 27.66 

Ash (percent) 279 2.86 25.06 6.44 

Total sulfur (percent) 279 0.06 2.40 0.48 

Gross calorific value (Btu) 277 3,740 9,950 8,220 

LbSO2/million Btu 277 0.14 7.88 1.24 

Moist, mineral-matter free Btu 277 4,580 10,560 8,820 

Antimony 144 0.01L 17 0.49

Arsenic 158 0.20L 19 2.6

Beryllium 151 0.078L 3.3 0.54

Cadmium 151 0.007L 3.0 0.21

Chromium 161 0.59L 50 6.1

Cobalt 160 0.38L 27 1.9

Lead 162 0.50L 17 3.0

Manganese 161 0.18 210 26

Mercury 162 0.006L 27 0.13

Nickel 161 0.71L 35 4.6

Selenium 151 0.08L 16 1.1

Uranium 157 0.11L 12 1.3

Original analytical data from which these values were calculated consists of proximate and 

ultimate analyses and trace element analyses from the U.S. Geological Survey COALQUAL 

database (Bragg and others, 1994). Table 3 reports a range in Wyodak-Anderson total sulfur 

content of 0.06 to 2.4 percent with a mean of 0.48 percent, and a range in ash yield of from 2.86 

to 25.06 percent with a mean of 6.44 percent. Pounds of SO2 per million Btu for WyodakAnderson coal ranged from 0.14 to 7.88 with a mean of 1.24 and the gross calorific value of the 

coal ranged from 3,740 to 9,950 Btu/lb, with a mean of 8,220 Btu/lb

11 
CHARACTERISTICS AND QUALITY OF WYODAK-ANDERSON AND OTHER COAL 

IN THE GILLETTE COAL FIELD, WYOMING 

The Wyodak-Anderson coal zone in the 

Gillette coal field includes (from upper to 

lower) the Smith, Swartz, Anderson, 

Wyodak, Canyon, and Werner coal beds 

(Ellis and others, 1999). These beds are in 

the late Paleocene Tongue River Member of 

the Fort Union Formation (fig. 3). WyodakAnderson coal quality in the Gillette coal 

field study area (tables 4, 5, and 6) is very

similar to that shown for the WyodakAnderson coal throughout the Powder River 

Basin (table 3).

Table 4. Coal quality summary data using 

weighted averages, one value for each parameter 

at each data point location, for Wyodak-Anderson 

coal in the Gillette coal field. The table was 

modified from Ellis and others (1999). Proximate 

and ultimate analyses are reported on an asreceived basis. Trace elements are reported in 

parts per million. L indicates that the value was 

below the detection limit for the measuring device 

12 

Coal Quality Range 

Parameter 

Number of 

samples Minimum Maximum 

Mean 

Moisture (percent) 108 14.5 42.30 27.47 

Ash (percent) 87 3.5 25.06 7.45 

Total sulfur (percent) 87 0.20 1.16 0.48 

Gross calorific value (Btu) 85 3,740 9,950 8,220 

LbSO2/million Btu 85 0.44 3.27 1.25 

Moist, mineral-matter free Btu 85 4,580 10,560 8,910 

Antimony 49 0.01L 17 0.72

Arsenic 62 0.20L 19 2.3

Beryllium 64 0.078L 3.3 0.35

Cadmium 56 0.007L 3.0 0.39

Chromium 65 0.59L 50 7.0

Cobalt 65 0.38L 27 2.3

Lead 66 0.50L 17 2.9

Manganese 66 0.18 210 22

Mercury 66 0.006L 27 0.17

Nickel 66 0.71L 35 5.0

Selenium 56 0.08L 16 1.4

Uranium 61 0.11L 12 1.5
In the Gillette coal field there were a total of 108 locations from which samples were collected. 

Non-confidential data point locations in the coal field are shown in figure 8. Table 4 shows 

summary data for Wyodak-Anderson coal in the Gillette coal field. The values shown in this 

table are weighted averages of Wyodak-Anderson coal quality data at each of the 108 data point 

locations, one value for each coal quality parameter at each data point location. The table shows 

total sulfur content that ranged from 0.20 to 1.16 percent with a mean of 0.48 percent and ash 

yield that ranged from 3.5 to 25.06 percent with a mean of 7.45 percent. Pounds of SO2 per 

million Btu for Wyodak-Anderson coal in the coal field ranged from 0.44 to 3.27 with a mean of 

1.25 and the gross calorific value of the coal samples ranged from 3,740 to 9,950 Btu/lb with a 

mean of 8,220 Btu/lb (Ellis and others, 1999). 

Table 5. Proximate, ultimate and calorific values using all sample analyses, more than one sample at each 

data point location, from coal beds in the Wyodak-Anderson coal zone in the Gillette coal field. Calculated 

from data in Flores and others (1999) and from confidential sources. All values are reported on an asreceived basis. MmmfBtu is moist, mineral-matter free Btu 

Chemical parameter Number of 

samples 

Minimum 

value 

Maximum value Mean value 

Moisture (percent) 226 14.5 42.3 29.16 

Ash (percent) 226 2.5 32 7.05 

Total sulfur (percent) 227 0.1 4.6 0.54 

Gross calorific value (Btu) 161 4,690 9,950 7,870 

LbSO2/million Btu 161 0.2 6.43 1.62 

MmmfBtu 161 6,940 10,570 8,580

Organic sulfur (percent) 215 0.06 1.55 0.37 

Pyritic sulfur (percent) 199 0.01 3.09 0.16 

Sulfate sulfur (percent) 187 0.01 0.47 0.03 

Fixed carbon (percent) 226 4.1 44.5 33.41 

Volatile matter (percent) 226 21.4 55.7 30.38 

Table 6. Trace element content of coal samples from beds in the Wyodak-Anderson coal zone in the Gillette 

coal field. Calculated from data in Flores and others (1999). All values are reported in parts per million and 

are on a whole-coal and remnant-moisture basis 

Chemical 

parameter 

Number of 

samples 

Minimum value Maximum value Mean value 

Antimony 281 0.01 17 0.34

Arsenic 282 0.23 150 3.3

Beryllium 215 0.02 9.1 0.80

Cadmium 273 0.007 3.0 0.09

Chromium 285 0.59 66 7.2

Cobalt 284 0.27 27 2.1

Lead 286 0.14 20 2.9

Manganese 286 0.18 220 27

Mercury 229 0.006 27 0.11

Nickel 286 0.53 67 5.4

Selenium 273 0.05 16 1.0

Uranium 282 0.01 12 0.98

13 
A more detailed coal quality summary for each of the coal beds sampled from the WyodakAnderson coal zone in the Gillette coal field is shown in Tables 5 and 6. These two tables show 

proximate and ultimate analyses, gross calorific value, and selected trace element content of coal 

from over 200 sample analyses, more than one sample collected from most data point locations. 

The values reported for individual samples, shown in Tables 5 and 6, have a much larger range 

than are reported for the weighted averages, shown in Table 4. This difference in values indicates 

that the quality of coal produced can be customized through selective mining of coal beds, and 

blending of coal to meet individual coal quality standards. 

About 305 million short tons of coal were supplied to coal-fired powered power plants in 1999 

from coal mines in the Gillette coal field (fig. 2). According to the 2000 COALdat database 

(Resource Data International, Inc., 2000), coal supplied to electrical power plants in 1999 from

these mines had mean values of 0.31 percent total sulfur, 5.21 percent ash yield, 0.72 pounds of 

SO2 per million Btu, and gross calorific value of 8,630 Btu/lb. Table 7 shows the quality of coal 

produced from these mines, reported by location of the mines in the northern, middle, and 

southern parts of the coal field (fig. 2). 

Table 7. Summary of coal quality and production of coal from mines in the Gillette coal field supplied to 

coal-fired power plants in 1999 (Resource Data International, Inc., 2000). Coal quality parameters are listed 

by the location of the 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. Production is 

reported in millions of short tons (mst) and rounded to one decimal place 

Coal quality parameter and

1999 production Northern part Middle part Southern part Combined areas 

All mines in 

Gillette coal 

field 

Minimum ash (percent) 4.37 3.7 3.8 4.22 3.7

Maximum ash (percent) 9.3 45.03 18.9 5.5 45.03

Mean ash (percent) 5.66 5.39 5.11 4.68 5.21

Minimum total sulfur 

(percent) 0.23 0.21 0.15 0.25 0.15

Maximum total sulfur 

(percent) 1.05 0.7 5.32 0.4 5.32

Mean total sulfur (percent) 0.45 0.33 0.29 0.32 0.31

Minimum gross calorific 

value (Btu) 7,940 8,190 8,100 8,300 7,940

Maximum gross calorific 

value (Btu) 8,790 8,770 9,410 8,850 9,410

Mean gross calorific value 

(Btu) 8,300 8,430 8,770 8,490 8,630

Minimum lbSO2/million Btu 0.55 0.49 0.34 0.58 0.34

Maximum lbSO2/million Btu 2.53 1.71 12.13 0.95 12.13

Mean lbSO2/million Btu 1.09 0.78 0.66 0.76 0.72

Production (mst) 26.8 94.8 167.0 16.8 305.3

14 
QUALITY OF ECONOMICALLY EXTRACTABLE COAL BEDS ASSESSED IN THE 

GILLETTE COAL FIELD STUDY 

The recent USGS study of economically extractable coal in the Gillette coal field concentrated on 

five coal units. These units are currently designated, from upper to lower, as the Wyodak rider, 

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

equivalent to the Smith bed of Kent and others (1980) and the Roland/Badger of Pierce and others 

(1990). The Upper Wyodak is the same as the Upper Wyodak of Kent and others (1980). The 

Canyon is equivalent to the Canyon of Kent and others (1980), which is an upper split of the 

lower Wyodak/Werner. The lower Wyodak/Werner is equivalent to the lower Wyodak of Kent 

and others (1980), which includes the Werner of Pierce and others (1990). The Gates/Kennedy

coal is equivalent to the Gates of Kent and others (1980) and the upper Kennedy of Pierce and 

others (1990). Glass (2000) contains a fence diagram, modified from several U.S. Geological 

Survey publications, in which many of the coal bed correlations and bed names used in various 

parts of the Powder River Basin are clarified. This fence diagram shows the Anderson bed as 

equivalent to what is called the Upper Wyodak, the Gates coal as being equivalent to the Wall, 

and the Kennedy coal as equivalent to the Pawnee. 

To summarize, the coal units included in the Gillette study area are stratigraphically equivalent to 

(from uppermost to lowermost) the Roland, Smith, Badger, Wyodak, Anderson, Canyon, Werner, 

Gates or Wall, and Kennedy or Pawnee coal beds as defined in previous publications. All of 

these coal beds are subbituminous C in apparent rank. According to data from the recent study

and from statistics reported in Glass (2000), the coal beds included have a maximum thickness of 

about 200 ft (61 m), contain from 15 to 35 percent moisture and 0.13 to 2.3 percent total sulfur, 

have an ash yield of from 2.5 to 19.68 percent, have gross calorific values from 7,130 to 9,950 

Btu/lb, and have calculated values for pounds of sulfur dioxide per million Btu’s that range from

0.25 to 3.68. 

The data set used for this coal quality study of the economically recoverable coal beds in the 

Gillette coal field included analytical data from published sources (Bragg and others, 1994; Flores 

and others, 1999) and unpublished confidential data from various sources. The data set is made 

up of 140 samples for which proximate and ultimate analyses and heat of combustion were run on 

an as-received basis and 157 samples that were analyzed for content of potentially hazardous 

trace elements, measured in parts per million on a whole-coal and remnant-moisture basis. A 

summary of the coal quality data is shown in Tables 8 and 9. The data set does not include 

analyses for the Canyon or Gates/Kennedy coal, but Table 8 includes data for the Canyon bed 

from Glass (2000). 

15 
Table 8. Proximate and ultimate analyses and calorific values of economically extractable coal in the 

Gillette coal field. Proximate and ultimate analyses are reported in percent by weight. All analyses are 

reported on an on an as-received basis. No data was available for the Gates/Kennedy coal bed 

Parameter Data Wyodak 

rider 

Upper 

Wyodak 

Lower Wyodak/ 

Werner 

Wyodak rider, Upper 

Wyodak, and Lower 

Wyodak/Werner 

combined 

Canyon 

(Glass, 

2000) 

Moisture Number of samples 4 127 9 140 9 

 Minimum (percent) 20 15 25 15 26.5 

 Maximum (percent) 27 35 32 35 31.5 

 Mean (percent) 23 27 27 27 29.6 

Ash Number of samples 4 127 9 140 9 

 Minimum (percent) 9.7 2.5 4.2 2.5 3.1 

 Maximum (percent) 19.1 19.68 8.2 19.68 7.4 

 Mean (percent) 12.90 5.80 5.83 6.01 5.1 

Total sulfur Number of samples 4 127 9 140 9 

Minimum (percent) 0.80 0.13 0.20 0.13 0.14

 Maximum (percent) 1.50 2.30 0.40 2.30 0.92 

 Mean (percent) 1.13 0.46 0.27 0.46 0.34 

Organic Number of samples 4 116 9 129 

 sulfur Minimum (percent) 0.39 0.06 0.15 0.06 

 Maximum (percent) 0.83 1.10 0.37 1.10 

 Mean (percent) 0.60 0.32 0.23 0.32 

Pyritic Number of samples 4 103 8 115 

sulfur Minimum (percent) 0.07 0.01 0.01 0.01

 Maximum (percent) 1.09 1.63 0.04 1.63 

 Mean (percent) 0.56 0.14 0.03 0.15 

Sulfate Number of samples 1 96 8 105 

sulfur Minimum (percent) 0.01 0.01 0.01 0.01

Maximum (percent) 0.01 0.47 0.03 0.47 

Mean (percent) 0.01 0.03 0.02 0.03

Lb SO2 Number of samples 4 62 9 75 

/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

Gross Number of samples 4 62 9 75 9 

calorific Minimum (Btu) 7,890 7,170 7,580 7,170 7,540

 value Maximum (Btu) 9,410 9,950 8,980 9,950 8,610 

 Mean (Btu) 8,500 8,570 8,470 8,550 8,290 

Moist, Number of samples 4 62 9 75 

mineral- Minimum 9,160 8,250 8,310 8,250

matter free Maximum 10,560 10,570 9,410 10,570 

Btu Mean 9,880 9,190 9,040 9,210

Fixed Number of samples 4 127 140 9 9 

carbon Minimum (percent) 29.7 25.5 4.1 31.8 4.1 

 Maximum (percent) 33.1 44.5 44.5 38.4 39.3 

 Mean (percent) 30.8 35.0 34.8 34.6 33.6 

Volatile Number of samples 4 127 9 140 9 

matter Minimum (percent) 30.30 24.75 28.80 24.75 28.7 

 Maximum (percent) 37.80 37.80 55.70 55.70 33.3 

 Mean (percent) 33.23 31.71 33.50 31.87 30.7 

16 
Table 9. Values for potentially hazardous air pollutant trace elements in economically extractable coal in the 

Gillette coal field. Reported in parts per million on a whole-coal and remnant-moisture basis. No data was 

available for the Canyon or Gates/Kennedy coal beds 

Parameter Data Wyodak rider Upper Wyodak Lower Wyodak/ Werner All three coal beds 

Antimony Number of samples 4 138 10 152 

 Minimum 0.52 0.01 0.09 0.01 

 Maximum 1.2 2.7 1.04 2.7 

 Mean 0.76 0.21 0.38 0.24 

Arsenic Number of samples 4 139 10 153 

 Minimum 3.6 0.35 0.33 0.33 

 Maximum 65 30 3 65 

 Mean 20 2.1 0.88 2.5 

Beryllium Number of samples 4 118 9 131 

 Minimum 1.4 0.03 0.17 0.03 

 Maximum 4.2 9.1 1.7 9.1 

 Mean 2.4 0.51 0.44 0.56 

Cadmium Number of samples 4 133 10 147 

 Minimum 0.09 0.01 0.03 0.01 

 Maximum 0.52 0.72 0.12 0.72 

 Mean 0.25 0.07 0.05 0.07 

Chlorine Number of samples 4 107 9 120 

 Minimum 50 50 50 50 

 Maximum 50 700 50 700 

 Mean 50 157 50 146 

Chromium Number of samples 4 143 10 157 

 Minimum 14 0.81 1.7 0.81 

 Maximum 19 35 12 35 

 Mean 17 4.7 5.2 5.02 

Cobalt Number of samples 4 143 10 157 

 Minimum 3.2 0.28 0.71 0.28 

 Maximum 9.7 11 11 11 

 Mean 5.8 1.8 3.9 2.01 

Lead Number of samples 4 143 10 157 

 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 

Manganese Number of samples 4 143 10 157 

 Minimum 15 2.7 2.5 2.5 

 Maximum 85 86 17 86 

 Mean 44 16 8.3 16 

Mercury Number of samples 4 86 10 100 

 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 

Nickel Number of samples 4 143 10 157 

 Minimum 13 0.85 1.5 0.85 

 Maximum 21 39 9.3 39 

 Mean 17 5.1 6.2 5.5 

Selenium Number of samples 4 136 8 148 

 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 Number of samples 4 139 10 153 

 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 

17 
The Upper Wyodak coal in the Gillette coal field is of particular interest for future development, 

because it is laterally pervasive and reaches a maximum thickness of about 200 ft (61 m). The 

Upper Wyodak coal bed also has higher mean gross calorific value (8,569 Btu/lb), lower mean 

ash yield (5.8 percent), and lower mean total sulfur content (0.46 percent) than most other 

Wyodak-Anderson coal beds in the Gillette study area (Tables 8 and 10). 

Table 10. Comparison of coal quality of the Wyodak-Anderson coal in the Powder River Basin and in the 

Gillette coalfield (Flores and others, 1999; Ellis and others, 1999), and of the economically extractable coal 

beds and the Upper Wyodak coal bed in the Gillette coal field. Proximate, ultimate, and heat of combustion 

values are reported on an as-received basis. Trace elements are reported on a whole-coal and remnantmoisture basis. Btu is British thermal units; MmmfBtu is moist, mineral-matter free Btu; and ppm is parts per 

million 

Area of study and coal bed(s) analyzed 

Powder River Basin Gillette coal field 

Coal quality 

parameter 

Wyodak-Anderson coal 

from Flores and others, 

1999 

(weighted mean) 

Wyodak-Anderson 

coal from Ellis and 

others, 1999 

(weighted mean) 

Coal beds 

assessed for 

this study 

(mean) 

Upper Wyodak 

coal bed from 

this study 

(mean) 

Moisture (percent) 27.66 29.16 27 27 

Ash (percent) 6.44 7.05 6.01 5.80 

Total sulfur (percent) 0.48 0.54 0.46 0.46 

Gross calorific value 

(Btu) 8,220 7,874 8,554 8,569

MmmfBtu 8,820 8,581 9,211 9,193

Organic sulfur 

(percent) --- 0.37 0.32 0.32

Pyritic sulfur (percent) --- 0.16 0.15 0.14 

Sulfate sulfur (percent) --- 0.03 0.03 0.03 

Fixed carbon (percent) --- 33.41 34.8 35.0 

Volatile matter 

percent) --- 30.38 31.87 31.71

Arsenic (ppm) 2.6 3.3 2.5 2.1 

Mercury (ppm) 0.13 0.11 0.20 0.21 

Selenium (ppm) 1.1 1.0 1.01 1.01 

Uranium (ppm) 1.3 0.98 0.64 0.61 

CONCLUSION

Coal in the Powder River Basin, specifically the economically extractable coal in the Gillette coal 

field, is very desirable for future coal production. The beds are generally thick and relatively

close to the surface, making it economic to produce the coal through surface mining operations. 

The Wyodak-Anderson coal in the Powder River Basin and in the Gillette coal field and five 

economically extractable beds recently studied also low in total sulfur content and ash yields and 

18 
have relatively high gross calorific value, compared with coal from most other coal fields in the 

U.S. (Flores and others, 1999). 

Table 10 shows the quality of coal in the recent study compared with the quality of coal in the 

Wyodak-Anderson coal zone throughout the Powder River Basin (Stricker and Ellis, 1999) and in 

the Gillette coal field (Ellis and others, 1999). Wyodak-Anderson coal in the Powder River Basin 

has relatively low gross calorific value, with a range of 4,580 to 10,560 Btu and a mean of 8,820 

Btu. However, the low sulfur content and ash yield for economically extractable coal seams in 

the Gillette coal field; with a minimum value of 0.13 percent and a mean of 0.46 percent total 

sulfur and a minimum value of 2.5 percent and a mean of 6.01 percent ash yield (tables 8 and 10); 

makes it desirable to blend higher quality coal in these coal seams with lower quality coal to meet 

power plant emissions standards. The Upper Wyodak bed in the recent USGS study is of 

particular interest for future development, because it is thick, pervasive, and of high quality. 

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