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Chapter PA
ASHLAND COALFIELD, POWDER RIVER BASIN,
MONTANA: GEOLOGY, COAL QUALITY, AND COAL
RESOURCES
by S.B. Roberts,1 E.M. Wilde,2 G.S. Rossi,1 Dorsey Blake,1 M.S. Ellis,1
G.D. Stricker,1 A.M. Ochs,3 G.L. Gunther,3 J.H. Schuenemeyer,1 and
H.C. Power4
in U.S. Geological Survey Professional Paper 1625-A
1U.S. Geological Survey2Montana Bureau of Mines and Geology, Butte, Montana
3Consultant, U.S. Geological Survey, Denver, Colorado4University of Delaware, Newark, Delaware
PA-ii
Contents
Introduction...........................................................................................................................PA-1
Geologic Overview and Coal Stratigraphy....................................................................PA-2
Coal Quality..........................................................................................................................PA-6
Net Coal Thickness (Isopach) Map.................................................................................PA-7
Overburden Thickness (Isopach) Map...........................................................................PA-7
Coal Resources.....................................................................................................................PA-8
Sources of Data.................................................................................................................PA-11
Drill-hole Data.............................................................................................................PA-11
Geologic Map Data ....................................................................................................PA-12
Geographic Boundary Data......................................................................................PA-13
Acknowledgments............................................................................................................PA-14
References Cited................................................................................................................PA-15
Figures
PA-1. Index map showing the Ashland coalfield and vicinity, southeast
Montana.
PA-2. Index map showing 7.5’ and 30’ x 60’ quadrangle maps, Ashland coalfield,
southeast Montana.
PA-3. Map showing Federally owned coal, Ashland coalfield and vicinity,
southeast Montana.
PA-4. Index map showing the Knobloch coal resource unit assessment area,
Ashland coalfield, southeast Montana.
PA-5. Index map showing generalized bedrock geology, drill-hole locations, and
the Ashland coalfield boundary, southeast Montana.
PA-iii
Figures—continued
PA-6. Coal-bed terminology applied to the Knobloch coal resource unit and
associated coal beds, Ashland coalfield and vicinity, southeast Montana.
PA-7. Map showing the location of cross sections A-A’ and B-B’, Ashland
coalfield, southeast Montana.
PA-8. North-south cross section A-A’ showing proposed coal-bed correlations,
Ashland coalfield and vicinity, southeast Montana.
PA-9. West-east cross section B-B’ showing proposed coal-bed correlations,
Ashland coalfield and vicinity, southeast Montana.
PA-10. Net coal thickness (isopach) map of the Knobloch coal resource unit,
Ashland coalfield, southeast Montana.
PA-11. Overburden thickness (isopach) map for the Knobloch coal resource unit,
Ashland coalfield, southeast Montana.
Tables
PA-1. Net coal resources in the Knobloch coal resource unit in the Ashland
coalfield, Montana, reported by county, overburden thickness, net coal
thickness, and reliability categories
PA-2. Net coal resources in the Knobloch coal resource unit reported for 7.5’
quadrangles in the Ashland coalfield, Montana
PA-3. Net coal resources in the Knobloch coal resource unit, Ashland coalfield,
Montana, reported by county and Federal coal and surface ownership
PA-4. Computations of confidence intervals within reliability categories for
estimated total coal resources in the Knobloch coal resource unit in the
Ashland coalfield, Montana
PA-iv
Tables—continued
PA-5. Volumes and estimates of uncertainty for estimated total coal resources in
the Knobloch coal resource unit, Ashland coalfield, Montana, with
measurement error
PA-1
INTRODUCTION
The Ashland coalfield, as defined here, incorporates an area of some 520 square
miles in parts of Powder River and Rosebud counties in southeastern Montana (fig.
PA-1). The coalfield is named for the town of Ashland, which is on the banks of the
Tongue River just west and north of the main part of the coalfield. Access through
the area is provided by a limited network of U.S. highways and secondary or
unimproved roads.
The coalfield is defined by both geologic and geographic parameters. The western
boundary is delimited by the outcrop or burn line (clinker contact) of the Knobloch
coal bed, and the remaining boundary of the coalfield is defined primarily by
geographic limits of 7.5’ quadrangles within the study area (fig. PA-2). In the Cook
Creek Reservoir 7.5’ quadrangle, the boundary represents the geographic limit of
subsurface data of sufficient spacing for viable coal correlations. The Ashland
coalfield in this study is more areally restricted than the Ashland coalfield of Bass
(1932) (520 square miles versus 975 square miles), and encompasses all or part of
the Ashland, Beaver Creek-Liscom Creek, and Poker Jim-Odell Creek coal deposits
of Matson and Blumer (1973). Most of the coal in the Ashland coalfield is Federally
owned (fig. PA-3). Other than small wagon mines that produced coal locally for
ranchers in the early 1900’s (Bass, 1932), there has been no substantial coal mining
in the coalfield.
The Tongue River is west of the Ashland coalfield, and the central part of the
coalfield is dissected by the Otter Creek drainage (fig. PA-4). The majority of the
Ashland coalfield (approximately 66 percent) underlies the Custer National Forest.
Because section 522 (e) (2) (b) of the Surface Mining Control and Reclamation Act
PA-2
of 1977 [SMCRA; Public Law 95-87 (30 U.S.C. 1201 et seq.)] strictly prohibits
surface coal mining within the boundaries of Custer National Forest, this coal
resource assessment addresses only those lands within the coalfield that fall outside
the Forest boundaries (fig. PA-4).
GEOLOGIC OVERVIEW AND COAL STRATIGRAPHY
The Fort Union Formation (Paleocene) outcrops throughout the Ashland coalfield;
younger rocks of the Wasatch Formation (Eocene) are exposed in areas just south
of the coalfield (fig. PA-5). Fort Union strata exposed in the coalfield are included in
the Tongue River Member; the underlying Lebo Member of the Fort Union
Formation is present in outcrops north of the coalfield (fig. PA-5). Rocks of the
Tongue River Member are essentially flat-lying, and are composed primarily of
shale, sandy shale, sandstone and thick coal beds. The thickness of the Tongue River
Member in this area ranges between 1,150 ft and 1,660 ft (Bass, 1932).
Clinker, formed from the natural burning of coal beds (see, for example, Heffern
and Coates, 1997) is prevalent throughout the area, and clinker of the Knobloch coal
bed is a prominent feature of the coalfield (fig. PA-5). In places, clinker deposits
may attain a thickness of greater than 100 ft (Matson and Blumer, 1973), and clinker
cliffs and ridges typically support the extensive growth of Ponderosa pine.
Coal beds are present throughout the Fort Union Formation in the Ashland coalfield.
The Knobloch coal bed in the lower part of the Tongue River Member (fig. PA-6)
has been targeted as the priority coal resource assessment unit in the coalfield,
primarily because of its thickness and continuity. In this report, the single Knobloch
coal bed is designated as the Knobloch coal resource unit (fig. PA-6), following
PA-3
criteria used by Culbertson and Saperstone (1987). Within this framework, the term
“Knobloch coal resource unit” identifies the thick, single body of coal formed by the
merging of multiple beds in northern areas of the coalfield, as well as the uppermost
coal bed in the Knobloch coal zone in southern and eastern areas of the coalfield
where the thick coal bed has split (fig. PA-6). The Knobloch coal resource unit or its
interpreted equivalent has been identified in drill holes beyond the limits of the
Ashland coalfield; however, the paucity and distribution of data make correlations
difficult in the more peripheral areas, and for this reason, we have restricted our area
of Knobloch coal resource assessment to the Ashland coalfield as defined here (fig.
PA-4).
The net coal thickness (excluding partings) of the Knobloch coal resource unit
ranges from 3 to 71 ft, and the wide variability in thickness reflects the merging and
splitting of individual components comprising the coal resource unit. The coal beds
considered to comprise the Knobloch coal resource unit where several coal beds
have merged into one thick bed include the Knobloch (uppermost), Calvert, Nance,
Lay Creek, and Flowers-Goodale (lowermost) coal beds (Culbertson and
Saperstone, 1987; Sholes and Daniel, 1992; Wilde, in press) (fig. PA-6). The King
coal bed, which is present above the Knobloch coal bed in some areas, may merge
locally with the Knobloch coal resource unit (Culbertson and Saperstone, 1987;
Sholes and Daniel, 1992). The Lay Creek coal bed, which occurs stratigraphically
between the Knobloch coal bed and the underlying Flowers-Goodale coal bed in the
Foster Creek area (fig. PA-6) is interpreted to merge with the Knobloch coal
resource unit (Knobloch coal bed) in T. 2 S., R. 45 E., in the northern part of the
Ashland coalfield (see, for example, Sholes and Daniel, 1992). McKay (1976) and
Wilde (in press) have also identified a Lay Creek coal bed in the southern part of the
Willow Crossing 7.5’ quadrangle in T. 3 S., R. 45 E. In this area, the Lay Creek
PA-4
coal bed is about 100 ft below the Knobloch coal resource unit. The stratigraphic
relationship between the Lay Creek coal bed in the Willow Crossing 7.5’ quadrangle
and the Lay Creek coal bed as identified in the Foster Creek area is unclear.
However, the stratigraphic position of this coal bed in the Willow Crossing
quadrangle, which is well below the Knobloch coal resource unit, suggests that the
Lay Creek coal bed in the southern part of the Willow Crossing quadrangle may not
be equivalent to the Lay Creek coal bed in the Foster Creek area. Additionally, the
reader should note that we do not correlate the Flowers-Goodale bed in the Ashland
coalfield with the Flowers-Goodale coal bed in areas to the south and east of the
coalfield as has been done by previous workers (see, for example, Culbertson and
Saperstone, 1987; McClellan and Biewick, 1988). This is primarily because the
stratigraphic position of the “Flowers-Goodale” bed as identified in those previous
reports is as much as 100 to 150 ft below the Flowers-Goodale coal bed in the
Ashland coalfield, and we suggest that the Flowers-Goodale bed in the Ashland
coalfield pinches out in eastern and southern areas of the field (fig. PA-6). The
stratigraphic relationship between the Flowers-Goodale coal bed in the Foster Creek
area and the Flowers-Goodale coal bed as we identify it in the Ashland coalfield is
unclear, and no attempt at correlation is made in this study.
In areas east of the Ashland coalfield, the Knobloch coal resource unit (Knobloch
coal bed) is interpreted to be equivalent (in part) to the Sawyer coal bed (McClellan
and Biewick, 1988; Sholes and Daniel, 1992). Based on limited subsurface data, we
suggest that the Knobloch coal bed in the Foster Creek area may be stratigraphically
lower than the Knobloch coal bed in the Ashland coalfield. In the Greenleaf Creek-
Miller Creek area north of the coalfield, the Knobloch coal bed is identified below
the Sawyer coal bed and above the Rosebud coal bed (Matson and Blumer, 1973)
(fig. PA-6). Sholes and Daniel (1992) suggest that the Rosebud coal bed is
PA-5
equivalent to a lower split of the Knobloch coal bed, and based on available data, this
conclusion seems highly plausible.
Two lines of cross section (fig. PA-7) derived from drill-hole data, depict our
interpretations of Knobloch coal resource unit continuity within the Ashland
coalfield. Cross section A-A’ (fig. PA-8) depicts north-south correlations of the
Knobloch coal resource unit and associated coal beds in a 30 mile transect of the
coalfield. West-east cross section B-B’ (fig. PA-9) traverses some 22 miles of the
Ashland coalfield. The cross sections include natural-gamma (NG), spontaneous
potential (SP), and resistivity (RES) geophysical log profiles. The majority of the
natural-gamma logs are products of coal exploration drilling, whereas the
spontaneous potential and resistivity logs are from oil and gas test wells. The datum
is mean sea level (MSL) for both cross sections, and the horizontal distribution of
drill-hole control points along each line of section is scaled to reflect the relative map
distance between drill holes, although this horizontal scaling is approximate.
The log profiles used in the cross sections were constructed from reduced
geophysical logs. Where natural-gamma logs were used, the data point displays a
“mirrored” image of the log profile to highlight the response in coal beds.
Spontaneous potential and resistivity logs are displayed in tandem as is typical of
these geophysical log records in oil and gas exploration. In this area, coal beds are
characterized by low natural-gamma and high resistivity responses. Spontaneous
potential logs were used primarily for differentiating high resistivity responses in
sandstone from similar high resistivity responses characteristic in coal beds.
The main coal-bed split area and split line B (fig. PA-7) approximate areas of coal-
bed splitting associated with the Knobloch coal resource unit. The location of these
PA-6
areas is highly inferred and is based on drill-hole data used in this assessment, as
well as some modification of interpretations of Culbertson and Saperstone (1987).
The area of the coalfield north of the main coal-bed split area is where the Knobloch
coal resource unit is formed from the merging of multiple beds, and the single bed
reaches a thickness in excess of 70 ft. South and southeast of this area, the Nance
and Flowers-Goodale coal beds are interpreted to split from the Knobloch coal
resource unit (fig. PA-8). Split line B delimits the point where the Calvert coal bed
splits from the Knobloch coal resource unit.
COAL QUALITY
Based on chemical analyses (as-received basis) from the Knobloch coal resource
unit in Tps. 3 and 4 S., R. 45 E. (Otter Creek EMRIA Site) (Culbertson and
Saperstone, 1987, after the U.S. Bureau of Land Management, 1975), the average
heat-of-combustion value for the Knobloch coal is 8,110 Btu/lb, the average ash
yield is 5.5 percent, and the average total sulfur content is 0.15 percent. The apparent
coal rank in this area is subbituminous C.
Based on as-received analyses, Matson and Blumer (1973) report calorific values
ranging from 7,761-9,070 Btu/lb, an ash yield ranging from 3.7-6.8 percent, and
total sulfur content ranging from 0.1-0.5 percent for the Knobloch coal bed in the
Ashland coal field. In the Foster Creek area (fig. PA-5), as-received analyses of the
Knobloch coal bed indicate heat-of-combustion values ranging from 7,380-7,840
Btu/lb, ash yield ranging from 6.7-8.7 percent, and total sulfur content from 0.3-1.6
percent (Matson and Blumer, 1973).
PA-7
In the Greenleaf Creek-Miller Creek area (fig. PA-5), Matson and Blumer (1973)
report as-received analyses of calorific value ranging from 8,209-8,935 Btu/lb, ash
yield ranging from 5.5-6.7 percent, and total sulfur content ranging from 0.42-0.44
percent for the Knobloch coal bed.
NET COAL THICKNESS (ISOPACH) MAP
The net coal thickness (isopach) map (fig. PA-10) is based on subsurface data from
202 drill holes, and is an interpretive map depicting the distribution and variation in
net coal thickness (excluding partings) of the Knobloch coal resource unit in areas of
the Ashland coalfield not included in Custer National Forest. Thicker net coal is
represented by warmer color shades (red and yellow), whereas cooler shades (blue)
represent areas of minimum net coal thickness.
Net coal thickness for the Knobloch coal resource unit varies from a minimum of 3
ft to a maximum of 71 ft. The thickest coal is found in areas north of the main coal-
bed split area (Tps. 2-4 S., Rs. 44-46 E.), where multiple beds have coalesced to
form a single thick coal body that typically ranges from 40 to 70 ft in thickness. The
Knobloch coal resource unit generally thins southward, with minimum net coal in
the southwestern part of the coalfield (T. 6 S., Rs. 42-46 E.) shrinking to 3 ft or less
(fig. PA-10).
OVERBURDEN THICKNESS (ISOPACH) MAP
The overburden thickness (isopach) map (fig. PA-11) is an interpretive map
showing the thickness of rock estimated to overlie the top of the Knobloch coal
PA-8
resource unit. In the Ashland coalfield, the overburden thickness in areas outside
Custer National Forest ranges from 0 at points along the Knobloch coal bed
outcrop/burn line (clinker contact) to more than 1,000 ft in the southwestern part of
the coalfield. Areas of thicker overburden are represented by shades of green and
yellow, while areas of less overburden are highlighted by shades of blue.
Comparison of the overburden and net coal thickness maps for the Knobloch coal
resource unit indicate that the thickest coal (north of the main coal-bed split area; fig.
PA-10) is present under overburden ranging typically from 0 to 500 ft thick (fig.
PA-11).
COAL RESOURCES
Coal resource estimates for the Knobloch coal resource unit are reported in tables
PA-1 through PA-3. In table PA-1, resources are tabulated by county, net coal
thickness categories, and overburden categories. Table PA-2 includes a summary of
coal resources reported by 7.5’ quadrangle, and table PA-3 includes a summary of
coal resources reported by county and Federal surface and subsurface ownership
criteria. It is important to note that these resource estimates are not comparable to
‘reserve’ estimates, and therefore, do not reflect in any way the amount of coal that
can be economically produced at the present time.
The quantification of coal resources in the Ashland coalfield follows a scheme of
resource calculation reported in Wood and others (1983). The basic quantification
formula is as follows: R = A x T x C,
where
R is the coal resource estimate (in short tons)
PA-9
A is the area underlain by coal (in acres)
T is the net coal thickness (in feet; excluding partings) based on isopach grids,
and
C is a weight/unit volume (density) conversion factor (in short tons/acre-foot).
All resources are reported in millions of short tons and are reported in accordance
with criteria established by Wood and others (1983). Coal tonnages were calculated
for net coal-bed thickness greater than 2.5 ft using an average density (C) for
subbituminous coal of 1,770 short tons per acre-foot. Tonnage values are rounded to
two significant figures and the tabulated totals may not equal the sum of the
components because of independent rounding. Coal resources are not tabulated for
areas within the Custer National Forest. However, based on data used in this study,
it is estimated that an additional 10-11 billion short tons of coal in the Kobloch coal
resource unit may underlie those areas of Custer National Forest included within the
Ashland coalfield as defined here.
Reported reliability categories (table PA-1) include measured, indicated, inferred,
and hypothetical coal resources. Measured resources occur within a 0.25-mile radius
of a data point, indicated resources within the area between 0.25 miles and 0.75
miles from a data point, and inferred resources are present within a radius from 0.75
miles to 3 miles surrounding a data point. Hypothetical resources are present in
areas more than 3 miles beyond a data point (Wood and others, 1983). Overburden
categories (table PA-1) represent the thickness of overburden above the top of the
Knobloch coal resource unit.
Confidence limits and estimates of uncertainty for total coal resources in the
Knobloch coal resource unit are shown in table PA-4 and table PA-5, respectively.
PA-10
A confidence interval is a statistic designed to capture uncertainty associated with a
point estimate. Confidence limits reported here are based on net coal thickness
measurements from 187 drill-hole locations. From these data, we computed 90-
percent confidence intervals on the volume of coal in the Knobloch coal resource
unit in the measured, indicated, inferred, and hypothetical categories. In this case,
volume refers to the calculated resource in millions of short tons (MST).
The confidence limits were derived through a complex series of steps. These steps
included modeling coal thickness trends and removing the trends using a
nonparametric regression algorithm called loess (with span = 0.75), and using
residual thickness to compute a semivariogram and fitting the semivariogram to a
spherical model. Parameter estimates were sill = 47.03 ft2, nugget = 10.37 ft2, and
range = 4.70 miles. Standard deviations of coal thickness were obtained from the
semivariogram model. Differences in point densities were compensated for by
calculating sample size, called pseudo n, within each reliability category and
calculating the variability of volume for each of the reliability categories. The volume
of coal in the Knobloch coal resource unit was then calculated at a 90-percent
confidence interval with measurement error. A description of the methodology used
is given in Schuenemeyer and Power (1998) and Ellis and others (1999).
The three main potential sources of error that might bias the confidence intervals are
preferential sampling, measurement errors, and model fitting. The probabilistic
interpretation of a confidence interval is based upon a random sample, which does
not exist in this situation, because there is preferential sampling in those areas
deemed to be minable. Measurement error can be caused by an error in recording
the coal-bed thickness or in the definition of coverage areas. Modeling fitting
variability and bias result from the choice of models and fitting procedures.
PA-11
SOURCES OF DATA
DRILL-HOLE DATA
The following drilling reports contain much of the drill hole information used in this
study, although additional point data was collated from the U.S. Geological Survey
National Coal Resources Data System (NCRDS), unpublished field logs, and from
a limited set of proprietary records. Collectors and compilers of these data files
include W.C. Culbertson, E.J. McKay, M.W. McClellan, and L.R.H. Biewick of the
U.S. Geological Survey.
Culbertson, W.C., Gaffke, T.M., and Correia, G., 1980, Coal exploratory holes
drilled in 1978-79 in the Birney 1° x 1/2° quadrangle, Big Horn and Rosebud
Counties, Montana, for coal beds in the Tongue River Member of the
Paleocene Fort Union Formation: U.S. Geological Survey Open-File Report
80-55, 68 p.
Hansen, W.B., and Culbertson, W.C., 1985, Correlated lithologic logs and analyses
from 1982 coal drilling in Big Horn, Prairie, Rosebud, and Treasure
Counties, Montana: U.S. Geological Survey Open-File Report 85-738, 125 p.
Kirschbaum, M.A., Correia, G.A., and McPhillips, M., 1982, Coal exploratory
drilling during 1979 in western Powder River County, Montana: U.S.
Geological Survey Open-File Report 82-748, 141 p.
PA-12
U.S. Geological Survey and Montana Bureau of Mines and Geology, 1977,
Geophysical logs for Big Horn, Fallon, and Powder River Counties,
Montana; Chapter A of preliminary report of 1977 coal drilling in eastern
Montana and northeastern Wyoming: U.S. Geological Survey Open-File
Report 77-721-A, 77 p.
_____ 1982, Coal drilling during 1980 in Big Horn, Dawson, McCone, Powder
River, Prairie, Richland, Rosebud, and Treasure Counties, Montana: U.S.
Geological Survey Open-File Report 82-026, 256 p.
GEOLOGIC MAP DATA
Derkey, P.M., 1986, Coal stratigraphy of the Lame Deer quadrangle, southeastern
Montana: Montana Bureau of Mines and Geology Geologic Map No. 43,
scale 1:100,000.
Matson, R.E., and Blumer, J.W., 1973, Quality and reserves of strippable coal,
selected deposits, southeastern Montana: Montana Bureau of Mines and
Geology Bulletin 91, 135 pages with plates.
Culbertson, W.C., U.S. Geological Survey, unpublished map compilation, 1970-
1987.
PA-13
GEOGRAPHIC BOUNDARY DATA
Federal lands and mineral status from:
Biewick, L.R.H., Urbanowski, S.R., Cain, Sheila, and Neasloney, Larry, 1998,
Land status and Federal Mineral ownership in the Powder River Basin,
Wyoming and Montana: a digital data set for geographic information
systems: U.S. Geological Survey Open File Report 98-108, coverage scale
1:100,000.
U.S. Bureau of Land Management, 1980, Surface and mineral management status
map, Lame Deer 30’ x 60’ quadrangle, Montana, scale 1:100,000.
U.S. Bureau of Land Management, 1980, Surface and mineral management status
map, Birney 30’ x 60’ quadrangle, Montana, scale 1:100,000.
U.S. Bureau of Land Management, 1980, Surface and mineral management status
map, Broadus 30’ x 60’ quadrangle, Montana, scale 1:100,000.
U.S. Bureau of Land Management, 1980, Surface and mineral management status
map, Powderville 30’ x 60’ quadrangle, Montana, scale 1:100,000.
State and County boundary data from U.S. Geological Survey National Mapping
Division and based on 1990 TIGER files digitally compiled by the Water Resources
Division of the U.S. Geological Survey.
PA-14
Digital coverages of 1:100,000- and 1:24,000-scale quadrangle map index acquired
from National Mapping Division, U.S. Geological Survey.
Public Land Survey System (PLSS) data from Montana Natural Resource
Information System (NRIS), Montana State Library, scale 1:100,000.
Digital hydrologic coverage from U.S. Environmental Protection Agency, Reach
File Version 3, scale 1:100,000.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the diligent and exhaustive efforts of W.C.
Culbertson (Emeritus, USGS) in his past field studies and compilation of pertinent
stratigraphic and geologic information that was critical to the completion of this
study. His foundation of published and unpublished work facilitated our study in
many ways. We also thank Laura Roberts for her expertise in resource calculation
methodology, Laura Biewick, and Shane Urbanowski their diligence in creating
accurate and available digital coverages of Federal Lands and Minerals ownership
status, David Ferderer for locating, obtaining, and formatting public domain files of
road and drainage networks in Montana, Gerald Sullivan for his GIS coverage
development in the initial stages of the project, and Jim Hunsicker for his
compilation of coal quality information. This report also benefited greatly from the
thoughtful comments and reviews of Mitch Henry (USGS, Denver, CO), Tim
Rohrbacher (USGS, Denver, CO), Craig Brunstein (USGS, Denver, CO), and
Katharine Varnes (USGS, Denver, CO).
PA-15
REFERENCES CITED
Bass, N.W., 1932, The Ashland coalfield, Rosebud, Powder River, and Custer
Counties, Montana: U.S. Geological Survey Bulletin 831, p. 19-105.
Culbertson, W.C., 1987, Diagrams showing proposed correlation and nomenclature
of Eocene and Paleocene coal beds in the Birney 30’ x 60’ quadrangle, Big
Horn, Rosebud, and Powder River Counties, Montana: U.S. Geological
Survey Coal Investigations Map C-113, plates with text.
Culbertson, W.C., and Saperstone, H.I., 1987, Structure, coal thickness, and
overburden thickness of the Knobloch coal resource unit, Birney area, Big
Horn, Rosebud, and Powder River Counties, Montana: U.S. Geological
Survey Coal Investigations Map C-112, scale 1:100,000.
Ellis, M.S., Gunther, G.L., Flores, R.M., Ochs, A.M., Stricker, G.D., Roberts,
S.B., Taber, T.T., Bader, L.R., and Schuenemeyer, J.H., 1999, Preliminary
report on coal resources of the Wyodak-Anderson coal zone, Powder River
Basin, Wyoming and Montana: U.S. Geological Survey Open-File Report
98-789A, 49 p.
Gilmour, E.H., and Williams, L.A., 1969, Geology and coal resources of the Foster
Creek coal deposit, eastern Montana: Montana Bureau of Mines and Geology,
Bulletin 73, 9 p.
PA-16
Heffern, E.L., and Coates, D.A., 1997, Clinker--Its occurrence, uses, and effects on
coal mining in the Powder River Basin: Wyoming State Geological Survey,
Public Information Circular 38, p. 151-165.
Matson, R.E., and Blumer, J.W., 1973, Quality and reserves of strippable coal,
selected deposits, southeastern Montana: Montana Bureau of Mines and
Geology Bulletin 91, 135 pages with plates.
McClellan M.W., and Biewick, L.R.H., 1988, Stratigraphic framework of the
Paleocene coal beds in the Broadus 30’ x 60’ quadrangle, Powder River
Basin, Montana-Wyoming: U.S. Geological Survey Coal Investigations Map
C-119-A; scale 1:100,000.
McKay, E.J., 1976, Preliminary geologic map and coal sections of the Willow
Crossing quadrangle, Rosebud and Powder River counties, Montana: U.S.
Geological Survey Miscellaneous Field Studies Map MF-802, 1:24,000.
Schuenemeyer, J.H., and Power, H., 1998, An uncertainty estimation procedure for
U.S. coal resources, [abs.], in Pittsburgh Coal Conference, 15th Annual
Meeting, Abstracts with Programs (CD-ROM): Pittsburgh, Pennsylvania, 13
p.
Sholes, M.A., and Daniel J.A., 1992, The Knobloch coal bed, Powder River and
Rosebud Counties, Montana: Correlation and petrography, in Sholes, M.A.,
Coal Geology of Montana: Montana Bureau of Mines and Geology, Special
Publication 102, p. 105-135.
PA-17
U.S. Bureau of Land Management, 1975, Resource and potential reclamation
evaluation, Otter Creek study site: U.S. Bureau of Land Management
EMRIA Report No. 1, 200 p.
Wilde, E.M., (in press), Available coal resources of the Willow Crossing 7.5-
minute quadrangle, Rosebud and Powder River counties, Montana: to be
published as a Montana Bureau of Mines and Geology Open-File Report.
Wood, G.H., Jr., Kehn, T.M., Carter, M.D., and Culbertson, W.C., 1983, Coal
Resource Classification System of the U.S. Geological Survey: U.S.
Geological Survey Circular 891, 65 p.
106° 00'106° 30'
106° 30'106° 00'
45° 30'45° 30'
45° 45'45° 45'
45° 15'45° 15'
Stacey
Birney
Otter
Quietus
Sayle Hall
Moorhead
Epsie
Volborg
Ashland
Brandenberg
312
212
212
North
Northern Cheyenne IndianReservation (part)
Powde
r Rive
r
Tongue River
Tong
ue R
iver
212U.S. Highway
Secondary and unimproved roads
County line
0 5 10 Miles
Rosebud coal mine(part)
Big Sky coal mine(part)
Ros
ebud
Cou
nty
Pow
der
Riv
er C
ount
y
Big Horn County
Rosebud County Custer County
Ashland coalfield
Ashland coalfield
Coal mine area
Northern Cheyenne Indian Reservation (part)
Explanation
Montana
Study Area
Knobloch coal bedoutcrop/burn line
Knobloch coal bedoutcrop/burn line
T.2N.
T.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
T.8S.
T.9S.
R.42E. R.43E. R.44E. R.45E. R.46E. R.47E. R.48E. R.49E.
Figure PA-1. Index map showing the Ashland coalfield and vicinity, southeast Montana.
106° 00'106° 30'
106° 30' 106° 00'
45° 30'
45° 45'
45° 15'45° 15'
0 5 10 Miles
Stacey
Birney
Otter
Brandenberg
Ashland
North
Northern Cheyenne IndianReservation (part)
Powde
r Rive
r
Tongue River
Tong
ue R
iver
Boundary separating adjacent30' x 60' quadrangles
Big Sky coal mine(part)
Ashland coalfield
Ashland coalfield
Coal mine area
Northern Cheyenne Indian Reservation (part)
ExplanationMontana
Study AreaKnobloch coal bedoutcrop/burn line
Figure PA-2. Index map showing 7.5' and 30' x 60' quadrangle maps, Ashland coalfield,southeast Montana.
Birney 7.5'quadrangle
Browns Mountain7.5' quadrangle
Poker Jim Butte7.5' quadrangle Fort Howes
7.5' quadrangle
Yager Butte7.5' quadrangle
Coleman Draw7.5' quadrangle
Ashland 7.5'quadrangle
Green Creek7.5' quadrangle
Powderville 30' x 60'quadrangle
Broadus 30' x 60'quadrangle
Broadus 30' x 60'quadrangle
Birney 30' x 60'quadrangle
Lame Deer 30' x 60'quadrangle
Cook Creek Reservoir7.5' quadrangle
Willow Crossing7.5' quadrangle
King Mountain7.5' quadrangle
Birney Day School7.5' quadrangle
Goodspeed Butte7.5' quadrangle
45° 30'
45° 45'
T.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
R.42E. R.43E. R.44E. R.45E. R.46E. R.47E. R.48E. R.49E.
T.2N.
T.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
T.8S.
T.9S.
R.42E. R.43E. R.44E. R.45E. R.46E. R.47E. R.48E. R.49E.
106° 00'106° 30'
106° 30' 106° 00'
45° 30'
45° 45'
45° 15'
0 5 10 Miles
Stacey
Ashland
Birney
Otter
Quietus
Sayle Hall
Moorhead
Brandenberg
Epsie
Volborg
Ashland coalfieldboundary
Custer National Forest
Northern Cheyenne Indian Reservation(part)
Tong
ue R
iver
Powde
r Rive
r
Tongue R
iver
Rosebud Mine (part)
Big Sky Mine (part)
North
Montana
Study AreaFederally owned coal
Federally owned coalCuster National Forest
Northern Cheyenne Indian Reservation
Coal mine
Knobloch coal bedoutcrop/burn line
Explanation
Figure PA-3. Map showing Federally owned coal, Ashland coalfield and vicinity,southeast Montana.
106° 00'106° 30'
106° 30' 106° 00'
45° 30'45° 30'
45° 45'45° 45'
45° 15'45° 15'
0 5 10 Miles
Stacey
Birney
Otter
BrandenbergT.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
R.42E. R.43E. R.44E. R.45E. R.46E. R.47E. R.48E. R.49E.
North
Northern Cheyenne IndianReservation (part)
Powde
r Rive
r
Tongue River
Otter C
reek
Tong
ue R
iver
Pum
pkin
Cre
ek
Big Sky coal mine(part)
Coal mine area Priority coal assessment area—Knobloch coal resource unit
Custer National Forest (part)
Northern Cheyenne Indian Reservation (part)
Perennial or intermittent stream
Explanation Montana
Study Area
Ashland coalfieldboundary
Ashland
Figure PA-4. Index map showing the priority coal assessment area, Ashland coalfield,southeast Montana.
T.2N.
T.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
T.8S.
T.9S.
R.42E. R.43E. R.44E. R.45E. R.46E. R.47E. R.48E. R.49E.
106° 00'106° 30'
106° 30' 106° 00'
45° 30'
45° 45'
45° 15'
0 5 10 Miles
Stacey
Ashland
Birney
Otter
Quietus
Sayle Hall
Moorhead
Brandenberg
Epsie
VolborgFoster CreekArea
Greenleaf Creek-Miller Creek Area
SouthernArea
EasternArea
Ashland coalfieldboundary
Custer National Forest (part)
Northern Cheyenne Indian Reservation(part)
Tong
ue R
iver
Powde
r Rive
rTo
ngue Rive
r
Rosebud mine (part)
Big Sky mine (part)
North
Montana
Study Area
Tw
Tftr
Tftr
Tftr
TflTfl
Tfl
Tfl
Tftr
Tw
Tftr
Tfl
Tw
Wasatch Formation
Fort Union Formation
Custer National Forest (part)
Northern Cheyenne Indian Reservation (part)
Coal mine area
Clinker (Knobloch coal bed)
Knobloch coal bed Drill hole penetrating Knobloch coal resource unitor stratigraphically equivalent horizon
Explanation
outcrop
burn line
Figure PA-5. Index map showing generalized bedrock geology, drill-hole locations, and theAshland coalfield boundary, southeast Montana. Geology based on Matson and Blumer (1973),Lewis and Roberts (1976), and Derkey (1986).
Tongue River Member. Also present in Custer National Forest andin the Northern Cheyenne Indian Reservation as shown
Lebo Member
Flowers-Goodale * (lower split)
Flowers-Goodale * (upper split)
Nance
North South
West East
Southern Area
Foster Creek area coal bedsGreenleaf Creek-Miller Creek areacoal beds
Eastern Area
* Based on coal bed terminology ofCulbertson and Saperstone (1987)
* Based on coal bed terminology and correlationsof Culbertson and Saperstone (1987)
* Based on coal bed terminology of Gilmour and Williams (1969)Coal bed terminology of Matson and Blumer (1973)
** Based on coal bed terminology of Sholes and Daniel (1992)
** Based on coal bed terminology and correlationsof McClellan and Biewick (1988)
Calvert
NanceFlowers-Goodale
Knobloch
Kno
bloc
h
Kno
bloc
h
King (Sawyer)
Flowers-Goodale *Flowers-Goodale **
Nance Nance? (Knobloch **)
Flowers-Goodale *
(alternative correlation)
Flowers-Goodale *
(alternative correlation)
Knobloch (Sawyer **)
Flowers-Goodale
Flowers-Goodalepinchout (this study)
Flowers-Goodale pinchout (this study)
Knobloch coal zone
X X'
Y Y'
Knobloch*
Knobloch
Sawyer
Rosebud
Lay Creek**
Flowers-Goodale*
Knobloch coal zone
Diagram not to scale
Diagram not to scale
Diagram not to scale
?
(Knobloch coal resource unit)
(Knobloch coal resource unit) (Knobloch coal resource unit)
(Knobloch coal resource unit)
Merges with the Knobloch coal bed in the Knobloch coalresource unit assessment area (Sholes and Daniel, 1992)
Ter
tiary
(pa
rt)
Pale
ocen
e (p
art)
Fort
Uni
on F
orm
atio
n
Tongue River Member
Lebo Member
Tullock Member
Roland
Waddle
AndersonDietz 2Dietz 3
Canyon
Cook
Otter
Wall
Poker Jim (Pawnee)
Odell (Cache)
Knobloch
SawyerKing
Flowers-Goodale Lay Creek
Terret (Kendrick ?)Witham
Stag
Generalized stratigraphic column showing coal beds/zones in the TongueRiver Member, Fort Union Formation, Ashland coalfield, Montana
Coal bed/zone
Figure PA-6. Coal-bed terminology applied to the Knobloch coal resource unit and associated coal beds, Ashland coalfield andadjacent areas, southeastern Montana. Terminology modified from Gilmour and Williams (1969), Matson and Blumer (1973),McKay (1976), Culbertson and Saperstone (1987), McClellan and Biewick (1988), and Sholes and Daniel (1992).
Diagram not to scale
106° 30' 106° 00'
45° 30'
45° 45'
45° 15'
0 5 10 Miles
Stacey
Ashland
Birney
Otter
Sayle Hall
Brandenberg
Epsie
Volborg
Foster CreekArea
Greenleaf Creek-Miller Creek Area
SouthernArea
EasternArea
Ashland coalfieldboundary
Custer NationalForest
Northern Cheyenne IndianReservation (part)
Tong
ue R
iver
Powde
r Rive
r
Tongue R
iver
North
Montana
Study Area
Knobloch coal resource unitassessment area
Custer National Forest (part)
Northern Cheyenne Indian Reservation (part)
X
X'
Y
Y'
Explanation
106° 00'106° 30'
106° 30'106° 00'
45° 30'45° 30'
45° 45'45° 45'
45° 15'45° 15'
0 5 10 Miles
Stacey
Birney
Otter
BrandenbergT.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
R.42E. R.43E. R.44E. R.45E. R.46E. R.47E. R.48E. R.49E.
?
North
Northern Cheyenne IndianReservation (part)
Powde
r Rive
r
Tongue River
Tong
ue R
iver
Knobloch coal resource unit assessment area
Custer National Forest (part)
Northern Cheyenne Indian Reservation (part)
ExplanationMontana
Study Area
Ashland coalfieldboundary
Ashland
Drill hole
Coal-bed split line(inferred location)
Coal-bed split area(inferred location)
Point ID
Figure PA-7. Map showing the location of cross sections A-A' and B-B', Ashlandcoalfield and vicinity, southeast Montana. The locations of the main coal-bed splitarea and coal-bed split line B are highly inferred and modified from Culbertson andSaperstone (1987).
Split line B
31-111LD
31-109LD
7-3B
7-36B
7-33B
24-2B
15-6B
15-2B
15-1B
24-6B
Main coal-bedsplit area
8-1B
32-15LD
32-145LD
32-144LD
31-34LD
31-33LD
1-21BR
2-5BR
A
B
B'
15-2B
A'
Flowers-Goodale pinchout(this study)
GL 3255 ft31-111LD
GL 3217 ft31-109LD
GL 3095 ft7-3B
GL 3140 ft7-33B
GL 3290 ft7-36B
15-6BGL 3789 ft
Total depth7825 ft
15-1BGL 4131 ft
15-2BGL 3420 ft
Lebo Member
Tullock Member(part)
24-2BGL 3811 ft
24-6B
GL 3884 ft
3100
3000
2900
2800
2700
2600
2500
2400
2300
2200
2100
2000
1900
3200
3300
3400
3500
3600
3700
3800
3900
4000
4100
4200
North South
Otter
Wall ?
Poker Jim
Poker JimOdell
Odell
Otter Otter
Brewster-Arnold
Ferry
CookCookCook
Flowers-Goodale (lower split)**
Flowers-Goodale (upper split)**
Terret
Stag
No
Rec
ord
No
Rec
ord
Total depth7247 ft
Total depth7584 ft
Total depth7466 ft
A A'
Elevation (in feet) above MSL
Cross section datum is MSL
Witham
Kendrick
Split line BMain coal-bed
split area
Nance
Nance
Nance
King (Sawyer)
Calvert
Flowers-
Goodale
King (Sawyer)
King (Sawyer)
?
?
??
Flowers-Goodale*
Tert
iary
(pa
rt)
For
t U
nion
For
mat
ion
(par
t)
Tong
ue R
iver
Mem
ber
(par
t)
NG
NG
NG
NG
NG
NG
NG
NG
NG
NG
SP RES
SP RES
1.2mi
2.2mi
1.3mi
2.5mi
8.0mi
1.3mi
4.5mi
5.4mi
3.7mi
Nance ?
Knobloch coal bed
Knobloch coal bed
2-5BRGL 3791 ft
"Mirrored" natural-gammalog traces (arrows indicatedecreasing natural-gamma) Spontaneous potential (SP) and
resistivity (RES) log traces (arrowsindicate negative (-) SP deflection and increasing resistivity.
Coal bed with parting
Coal bed 0
100 feet
Drill hole point IDSurface elevation (feet above MSL)
Drill-hole records
GL, Ground level (in feet)MSL, Mean sea level
Knobloch coal resource unit
Knobloch coal zone
Knobloch
King (Sawyer)
Coal bed name (alternate nomenclature)
Coal bed name
KCRU
KCRU
KCRU
KCRU
Knz
Knz
Knz
Knz
** Alternative Flowers-Goodale correlation and terminology of McClellan and Biewick (1988)
*Alternative Flowers-Goodale correlation and terminology of Culbertson and Saperstone (1987)
Explanation
Figure PA-8. North-south cross section A-A' showing proposed coal bed correlations, Ashland coalfield and vicinity,southeast Montana. Coal-bed and coal-zone terminology modified from unpublished drill-hole information (1996)of W.C. Culbertson and L.R.H. Biewick in the National Coal Resources Data System (NCRDS) of the U.S.Geological Survey. Location of the main coal-bed split area and split line B is highly inferred and modified fromCulbertson and Saperstone (1987).
No Record
Flowers-Goodale pinchout(this study)
Sawyer
Sawyer
Odell
Cook
Wall coal zone(or equivalent)
Otter
Odell (Cache)Brewster-Arnold
Witham
Witham
Terret
Knobloch coal bed (Sawyer )
Nance ?
Flowers-Goodale
Flowers-Goodale** (Broadus ?)
Kendrick (?)
31-34LDGL 3304 ft
31-33LDGL 3330 ft
32-145LDGL 3148 ft
32-15LDGL 3305 ft
32-144LDGL 3231 ft
8-1BGL 3558 ft
GL 3983 ft
GL 3791 ft2-5BR
3000
3100
3200
3300
3400
3500
2500
2400
2600
2700
2800
2900
3600
3700
3800
3900
4000
West East
No
Rec
ord
No
Rec
ord
No
Rec
ord
Total depth6400 ft
Total depth6836 ft
Total depth7128 ft
1-21BR
Poker Jim (Pawnee)
Poker Jim
B B'
Elevation (in feet) above MSL
Cross section datum is MSL
Tert
iary
(pa
rt)
For
t U
nion
For
mat
ion
(par
t)
Tong
ue R
iver
Mem
ber
(par
t)
Nance
NGNG
NG
NG
NG
NG
NGSP RES
2.8mi
3.1mi
1.7mi
3.0mi
3.8mi
3.4mi
4.2mi
Knobloch coal bed KCRU
KCRU
KCRU
NG
SP RES
2-5BRGL 3791 ft
"Mirrored" natural-gammalog traces (arrows indicatedecreasing natural-gamma) Spontaneous potential (SP) and
resistivity (RES) log traces (arrowsindicate negative (-) SP deflection and increasing resistivity.
Coal bed with parting
Coal bed 0
100 feet
Drill hole point IDSurface elevation (feet above MSL)
Drill-hole records
GL, Ground level (in feet)
MSL, Mean sea level
Knobloch coal resource unit
Knobloch coal zone
Knobloch
King (Sawyer)
Coal bed name (alternate nomenclature)
Coal bed nameKCRU
Knz
Knz
Knz
** Alternative Flowers-Goodale correlation and terminology of McClellan and Biewick (1988)
Explanation
Figure PA-9. West-east cross section B-B' showing proposed coal bed correlations, Ashland coalfield andvicinity, southeast Montana. Coal-bed and coal-zone terminology modified from unpublished drill-holeinformation (1996) of W.C. Culbertson and L.R.H. Biewick in the National Coal Resources Data System(NCRDS) of the U.S. Geological Survey. Location of the main coal-bed split area is highly inferred andmodified from Culbertson and Saperstone (1987).
Main coal-bedsplit area
2.5-10 ft
30-40 ft
50-60 ft
40-50 ft
60-70 ft
> 70 ft (maximum = 71 ft)
10-20 ft
20-30 ft
Explanation
Net coal thickness (in feet)
Custer National Forest (part)
Northern Cheyenne Indian Reservation (part)
Main coal-bed split area
Split line B
106° 00'106° 30'
106° 30' 106° 00'
45° 30'45° 30'
45° 45'45° 45'
45° 15'45° 15'
0 5 10 Miles
Stacey
Birney
Otter
Brandenberg
Ashland
T.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
R.42E. R.44E. R.46E. R.48E.
RosebudCounty
RosebudCounty
CusterCounty
Powder RiverCounty
Big Horn County
Main coal-bedsplit area
Split line B
Main coal-bedsplit area
North
Powde
r Rive
r
Tongue River
Tong
ue R
iver
Montana
Study Area
Ashland coalfieldboundary
Northern Cheyenne IndianReservation (part)
Figure PA-10. Net coal thickness (isopach) map of the Knobloch coal resource unit,Ashland coalfield, southeast Montana.
Custer National Forest(part)
Custer National Forest(part)
?
Drill hole (public data)
County line
Explanation
Overburden thickness (in feet)
0-100 ft
100-200 ft
200-500 ft
500-1000 ft
> 1000 ft
106° 00'106° 30'
106° 30' 106° 00'
45° 30'45° 30'
45° 45'45° 45'
45° 15'45° 15'
0 5 10 Miles
Stacey
Birney
Otter
Brandenberg
Ashland
T.1N.
T.1S.
T.2S.
T.3S.
T.4S.
T.5S.
T.6S.
T.7S.
R.42E. R.44E. R.46E. R.48E.
RosebudCounty
RosebudCounty
CusterCounty
Powder RiverCounty
Big Horn County
North
Powde
r Rive
r
Tongue River
Tong
ue R
iver
Montana
Study Area
Ashland coalfieldboundary
Northern Cheyenne IndianReservation (part)
County line
Custer National Forest (part)
Northern Cheyenne Indian Reservation (part)
Figure PA-11. Overburden thickness (isopach) map for the Knobloch coal resource unit,Ashland coalfield, southeast Montana.
Custer National Forest(part)
Custer National Forest(part)
Table PA-1. Estimated net coal resources for the Knobloch coal resource unit reported by county, overburden, net coal thickness, andreliability categories. Resources are reported in millions of short tons (MST) and with two significant figures. Zeros (0) indicate thatno coal resources were calculated within those categories. Reported resources do not include areas within Custer National Forest.Columns may not sum correctly because of independent rounding
County Overburden Net Reliability categories (distance from data point)thickness coal thickness Measured
(<1/4 mi)Indicated
(1/4-3/4 mi)Inferred
(3/4-3 mi)Hypothetical
(>3 mi)Total
(MST)POWDER RIVER 0-100 ft 10-20 ft 1.8 7.8 10 0 20
20-30 ft 33 88 100 0 22030-40 ft 23 21 17 0 6140-50 ft 20 44 8.4 0 7350-100 ft 110 360 140 0 610
0-100 ft total 190 520 280 0 980100-200 ft 10-20 ft 0.27 0 34 2.0 36
20-30 ft 17 46 52 0 11030-40 ft 14 20 18 0 5240-50 ft 43 56 49 0 15050-100 ft 310 720 260 0.91 1,300
100-200 ft total 380 840 410 2.9 1,600200-300 ft 10-20 ft 0 0 35 0.11 35
20-30 ft 6.7 14 39 0 5930-40 ft 0 11 12 0 2340-50 ft 6.7 23 72 0 10050-100 ft 170 460 210 0 840
200-300 ft total 180 510 370 0.11 1,100300-400 ft 10-20 ft 0 1.4 37 0 38
20-30 ft 1.7 5.9 15 1.5 2430-40 ft 0 2.2 4.9 0 7.140-50 ft 0 0.67 11 0 1250-100 ft 9.3 64 140 0 220
300-400 ft total 11 75 210 1.5 300
Table PA-1. Net coal resources, Knobloch coal resource unit—continued.
County Overburden Net Reliability categories (distance from data point)thickness coal thickness Measured
(<1/4 mi)Indicated
(1/4-3/4 mi)Inferred
(3/4-3 mi)Hypothetical
(>3 mi)Total
(MST)POWDER RIVER 400-500 ft 10-20 ft 0 0 16 0 16
20-30 ft 1.6 0.41 6.0 0.082 8.130-40 ft 0 0 0.29 0 0.2940-50 ft 0 0 2.9 0 2.950-100 ft 0 6.0 66 0 72
400-500 ft total 1.6 6.4 92 0.082 100500-1000 ft 10-20 ft 0 2.1 24 0 26
20-30 ft 0 0 0.74 0 0.7440-50 ft 0 0 12 0 1250-100 ft 0 0.36 16 0 17
500-1000 ft total 0 2.4 53 0 55POWDER RIVER total 770 1,900 1,400 4.6 4,100ROSEBUD 0-100 ft 5-10 ft 0.19 0.30 0 0 0.48
10-20 ft 12 56 35 0 10020-30 ft 26 61 0 0 8730-40 ft 5.7 22 9.8 0 3840-50 ft 13 29 12 0 5350-100 ft 11 81 130 0 230
0-100 ft total 68 250 190 0 510100-200 ft 2.5-5 ft 0 0.30 0 0 0.3
5-10 ft 1.1 8.3 7.8 0 1710-20 ft 21 53 24 0 9820-30 ft 32 39 4.4 0 7630-40 ft 2.7 14 0.18 0 1740-50 ft 5.2 5.9 0.58 0 1250-100 ft 31 82 28 0 140
100-200 ft total 93 200 64 0 360
Table PA-1. Net coal resources, Knobloch coal resource unit—continued.
County Overburden Net Reliability categories (distance from data point)thickness coal thickness Measured
(<1/4 mi)Indicated
(1/4-3/4 mi)Inferred
(3/4-3 mi)Hypothetical
(>3 mi)Total
(MST)ROSEBUD 200-300 ft 2.5-5 ft 0.24 0.06 0 0 0.30
5-10 ft 0.36 8.8 17 0 2610-20 ft 9.4 46 59 0 11020-30 ft 3.2 17 2.1 0 2230-40 ft 2.1 17 0.61 0 2040-50 ft 0 0.35 0 0 0.3550-100 ft 17 78 15 0 110
200-300 ft total 32 170 94 0 290300-400 ft 2.5-5 ft 0.078 0.56 0.12 0 0.75
5-10 ft 2.8 9.6 38 0 5010-20 ft 4.1 29 61 0 9420-30 ft 0.98 11 1.7 0 1430-40 ft 0 3.7 2.5 0 6.250-100 ft 4.4 24 3.3 0 32
300-400 ft total 12 78 110 0 200400-500 ft 2.5-5 ft 0.42 1.7 0.74 0 2.9
5-10 ft 1.9 11 26 0 3910-20 ft 1.3 17 60 0 7820-30 ft 0 2.9 1.9 0 4.830-40 ft 0 0.44 2.2 0 2.650-100 ft 1.2 9.3 0 0 11
400-500 ft total 4.8 42 91 0 140500-1000 ft 2.5-5 ft 0.10 0.79 0.076 0 0.97
5-10 ft 1.0 20 120 0.042 14010-20 ft 2.3 22 180 4.2 21020-30 ft 0.37 2.0 3.0 0 5.430-40 ft 0 0 0.18 0 0.1850-100 ft 0 0.66 0 0 0.66
500-1000 ft total 3.8 45 300 4.2 360
Table PA-1. Net coal resources, Knobloch coal resource unit—continued.
County Overburden Net Reliability categories (distance from data point)thickness coal thickness Measured
(<1/4 mi)Indicated
(1/4-3/4 mi)Inferred
(3/4-3 mi)Hypothetical
(>3 mi)Total
(MST)ROSEBUD 1000-1500 ft 5-10 ft 0 0 20 0 20
10-20 ft 0 0.16 4.4 0 4.520-30 ft 0 0 2.2 0 2.2
1000-1500 ft total 0 0.16 26 0 27ROSEBUD total 210 780 880 4.2 1900Grand total (MST) 980 2,700 2,300 8.8 6,000
Table PA-2. Net coal resources in the Knobloch coal resource unit reported by 7.5-minute quadrangle. Coal resources are reported inmillions of short tons (MST) and with two significant figures. Reported resources do not include areas within Custer National Forest.Column may not sum correctly because of independent rounding
7.5-minute quadrangle Total (MST)ASHLAND 330BIRNEY 620BIRNEY DAY SCHOOL 200BROWNS MOUNTAIN 280COLEMAN DRAW 1,000COOK CREEK RESERVOIR 300FORT HOWES 180GOODSPEED BUTTE 130GREEN CREEK 220KING MOUNTAIN 1,000POKER JIM BUTTE 56WILLOW CROSSING 1,400YAGER BUTTE 330Grand total (MST) 6,000
Table PA-3. Net coal resources in the Knobloch coal resource unit reported by county and by Federal coal and surface ownership.Resources within Custer National Forest are not included in the resource tabulation. Coal resources are reported in millions of short tons(MST) and with two significant figures. Column may not sum because of independent rounding
County Federal ownership Total (MST)POWDER RIVER No Federal coal or surface ownership 1,800
Federal coal, but no Federal surface ownership 2,100Federal coal and Federal surface ownership 200
POWDER RIVER total Federal coal 2,300POWDER RIVER total 4,100ROSEBUD No Federal coal or surface ownership 730
Federal coal, but no Federal surface ownership 790Federal coal and Federal surface ownership 360
ROSEBUD total Federal Coal 1,100ROSEBUD total 1,900Total Federal coal 3,400Grand total (MST) 6,000
Table PA-4. Computations of confidence intervals within reliability categories for the Knobloch coal resource unit, Ashland coalfield,Powder River Basin, Montana. Areas within Custer National Forest are not included in the table. Volume refers to the calculated resourcein millions of short tons (MST). NA, not applicable
Parameter Reliability category EntireMeasured Indicated Inferred Hypothetical area
Area (in square meters) 55,222,034 168,110,743 225,695,422 1,060,821 450,089,020Percent of area 12 37 50 0 100Acres 13,646 41,541 55,771 262 111,219SD (Standard deviation (in ft) from variogrammodel)
3.757 4.640 7.020 7.576 NA
Acre feet (Acres x SD) 51,264 192,732 391,488 1,986 NAVolume standard deviation (in millions of short tons(MST))
9 56 395 4 463
Pseudo n (Minimum number of points in the area) 109 37 3 1 NA
Table PA-5. Volume and estimates of uncertainty for resources in the Knobloch coal resource unit, Ashland coalfield, Powder RiverBasin, Montana with measurement error. Coal resources in the Custer National Forest are not included in the resource tabulation.Volume refers to the calculated resource in millions of short tons (MST). Resources are reported in millions of short tons (MST) withfour significant figures
Parameter Reliability Category EntireMeasured Indicated Inferred Hypothetical Area
Volume (MST) 979.5 2,729 2,285 8.800 6,003Lower 90% confidence bound (MST) 965.0 2,636 1,636 3.000 5,240Upper 90% confidence bound (MST) 994.0 2,822 2,934 14.60 6,764