Central Region Energy Resources Team


Coal availability in the Hilight quadrangle, Powder River Basin, Wyoming: a prototype study in a western coal field

by Carol L. Molnia, Laura R. H. Biewick, Dorsey Blake, Susan J. Tewalt, M. Devereux Carter (US Geological Survey), and Charlie Gaskill (Bureau of Land Management)

Open-File Report 97-469

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, product, or company names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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Background and Purpose of Study
Geologic Setting and Coal Mining
Factors Affecting Availability of Coal Resources
      Unsuitability Criteria Determinations for the Hilight Quadrangle
            (a) Unsuitability Criteria that are Restrictions to Mining
            (b) Unsuitability Criteria that are Considerations in Mining and Mine Planning
      Other Considerations to Mining (in addition to those in the Unsuitability Criteria)
            (a) Multiple-Use Issues
            (b) Technologic Factors
Grouping of Constraints to Mining in the Hilight Quadrangle
Major Coal Zones Studied
Computer Techniques
      Coal Availability Calculation   Using Category 1 Restrictions (Likely restrictions to mining)
      Coal Availability Calculation  Including Category 2 Restrictions   (Considerations that probably will be mitigated)
Comparison to Other Coal Availability Studies
Comparison to Other Coal Resource Calculations for the Quadrangle

Table 1. List of possible restrictions
Table 2. Constraints to mining in the Hilight quadrangle
Table 3. Summary of coal resources and available coal, by coal bed

Tables 4 -13. Coal Resource tables: the following 3 tables [a,b,c] for each bed listed below; for both Category 1 restrictions [present land-use and technologic restrictions] and Category 2 restrictions [possible additional land-use and technologic restrictions].

Figure 1. Map showing location of the Powder River Basin and the Hilight 7 1/2 -minute quadrangle.

Figure 2. Map showing locations of surface coal mines near the Hilight 7 1/2 -minute quadrangle.

Figure 3. Map showing data points used for this study.

Figure 4. Generalized composite stratigraphic section for the Hilight quadrangle.

Figure 5. Map of Hilight quadrangle showing area underlain by the Wyodak coal bed, and areas not available for surface mining because of land-use and technologic restrictions.

Figure 6. Map of Hilight quadrangle showing area underlain by the Wyodak coal bed, and showing other land-use and technologic considerations that would need to be resolved before surface mining could occur.

Figure 7. Map showing additional land-use features of the Hilight quadrangle.

Figure 8. Map of Hilight quadrangle showing areas where overburden for the Main Wyodak coal bed is less than 300 ft thick.

Figure 9. Coal correlation diagram showing representative sections from the Hilight study area.

Figure 10. Coal-correlation diagram A- A', showing coal beds in the Wyodak coal interval.

Figure 11. Enlargement of coal-correlation diagram A- A'.

Figure 12. Chart showing total original coal resources in the Hilight quadrangle.

Figure 13. Chart showing amount of available coal in Hilight quadrangle (Category 1 restrictions).

Figure 14. Chart showing proportions of Main, Rider, and Lower Wyodak coal beds that together make up the available coal for the Hilight quadrangle (Category 1 restrictions).

Figure 15. Chart showing three divisions of the Main Wyodak coal bed resources: available coal; coal restricted by land-use considerations; and coal restricted by technologic considerations (Category 1 restrictions).

Figure 16. Chart showing three divisions of the Rider Wyodak coal bed resources: available coal; coal restricted by land-use considerations; and coal restricted by technologic considerations Category 1 restrictions).

Figure 17. Chart showing three divisions of the Lower Wyodak coal bed resources: available coal; coal restricted by land-use considerations; and coal restricted by technologic considerations (Category 1 restrictions).

Figure 18. Chart showing land-use restrictions for the Main Wyodak coal bed (Category 1 restrictions).

Abbreviations and Conversions

To convert from

Inches (in.)
Feet (ft)
Miles (mi)
Short tons (2,000 lbs.)

Metric tons (2,204.6 lbs.)
Multiply by


     The U.S. Geological Survey (USGS), in cooperation with the Bureau of Land Management (BLM), Geological Survey of Wyoming, and U.S. Bureau of Mines (USBM), has produced an estimate of the amount of available coal in an area about 35 miles south of Gillette, Wyo., where the Wyodak coal bed is, in places, more than 100 ft thick. Available coal is the quantity of the total coal resource that is accessible for mine development under current regulatory, land-use, and technologic constraints. This first western coal availability study, of the Hilight 7 1/2-minute quadrangle, indicates that approximately 60 percent (2.7 billion short tons) of the total 4.4 billion tons of coal in-place in the quadrangle is available for development. (There has been no commercial mining in the Hilight quadrangle.) Approximately 67 percent (1.9 billion tons) of the Main Wyodak coal bed is considered available. All tonnage measurements in this report are given in short tons.

     Coal-development considerations in the quadrangle include dwellings, railroads, pipelines, power lines, wildlife habitat (eagles), alluvial valley floors, cemeteries, and the Hilight oil and gas field and gas plant. Some of these considerations could be mitigated so that surface mining of the coal may proceed; others could not be mitigated and would preclude mining in their vicinity. Other technological constraints that influence the availability of the coal include overburden thickness, coal beds too thin, and areas of clinker.

     We could not have successfully completed this project without the help of Vickie L. Clark, the U.S. Geological Survey computer system administrator. Employees of the U.S. Bureau of Mines Coal Recoverability Program -- Timothy J. Rohrbacher, Lee M. Osmonson, Gerald L. Sullivan, David C. Scott, and Dale D. Teeters -- were extremely helpful with describing local mining practice and assisting with GIS (geographic information systems) software. The Wyoming State Geological Survey supplied information and helped with project logistics. James E. Fassett and Timothy J. Rohrbacher reviewed the manuscript and offered thoughtful and constructive comments. Sally J. Dyson, Robert K. Wells, Cheryl W. Adkisson, and Richard P. Walker assisted in preparing a digital version of this report to appear as a World Wide Web release.

Background and Purpose of StudyContents
     Traditional Federal and State coal resource estimates have not taken into account the multitude of land-use, environmental, regulatory, technologic, and economic restrictions to coal mining and coal resource recoverability. This has led some Federal, State, and local planners to overestimate the future supply of the Nation's coal. A cooperative program, referred to as "Coal Availability," between the U.S. Geological Survey and other Federal agencies and State geological surveys, was initiated in 1986 to identify major constraints on the availability of coal resources for development and to estimate the amount of remaining coal resources that may be accessible for development under those constraints (Carter and Gardner, 1989, 1994; Eggleston and others, 1990). Coal availability studies have been done at the 7 1/2-minute-quadrangle scale; the results are modeled statistically and can be indicative of larger areas that have similar developmental restrictions and geologic conditions.

     The data generated during the coal availability studies were shared with the U.S. Bureau of Mines for use in their coal recoverability studies, where recovery and cost factors were applied to the estimated available coal resources. This results in an estimate of the amount of economically recoverable coal [coal reserves], which is usually far less than the amount available for development (Rohrbacher and others, 1994).

     The coal availability program was first conducted in the Eastern United States. The results there (see Comparison to Other Coal Availability Studies section of this report) were useful to the coal mining industry and other resource managers. Seventeen quadrangles were modeled in the central Appalachian region of West Virginia, Kentucky, and Virginia. Coal availability studies have expanded into the northern Appalachian region, the Illinois Basin, and the Western United States. There was great interest in extending the program to western coal fields to see what factors would be involved and how the process could be applied to the different geologic and mining conditions in the Western United States. The Hilight quadrangle study is the first coal availability study in the western United States.

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U.S. Geological Survey Open-File Report 97-469


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