**Coal Resource
Classification System of the U.S. Geological Survey**

By *Gordon H. Wood, Jr.,
Thomas M. Kehn, M. Devereux Carter, and William C. Culbertson*

GEOLOGICAL SURVEY CIRCULAR 891

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**CONTENTS**

1. Introduction
2. History of the
        classification system
3. Coal resource
        classification system
4. Glossary of coal
        classification system and supplementary terms
5. Criteria for coal
        resource classification
6. Applications of
        criteria
7. Specific criteria
8. Guidelines for
        estimating coal resources
9. General
        guidelines for classification of coal resources
10. Specific
        InstructionsRank of
                coal
            Overburden
            Thickness
                of coal categories
            Size of
                unit area
            Major
                categories of resources
            Coal
                bed maps
            Thickness
                of coal measurements
            Distribution
                of coal bed thickness measurements
            Measurement
                of areas
            Weight
                of coal per unit volume
            Calculation
                of coal resources
            Rounding
                of tonnage estimates
            Estimation
                of resources in the vicinity of where a coal bed
                bifurcates into two or more tongues
11. Rank of
                coal
12. Overburden
13. Thickness
                of coal categories
14. Size of
                unit area
15. Major
                categories of resources
16. Coal
                bed maps
17. Thickness
                of coal measurements
18. Distribution
                of coal bed thickness measurements
19. Measurement
                of areas
20. Weight
                of coal per unit volume
21. Calculation
                of coal resources
22. Rounding
                of tonnage estimates
23. Estimation
                of resources in the vicinity of where a coal bed
                bifurcates into two or more tongues
24. Estimation of
        hypothetical resourcesExtrapolated
                bed map method
            Extrapolated
                coal zone method
25. Extrapolated
                bed map method
26. Extrapolated
                coal zone method
27. Examples
        illustrating the basic geometric principles of
        constructing coal resource bed maps
28. Geophysical logs
        as a source of coal bed dataElectric logsSP log
                    Normal and lateral logs
                    Focusing-electrode and induction
                        logs
                    Discussion of electric logs
            Gamma ray log
            Density log
            Neutron log
            Acoustic velocity log
            Measurement of the coal bed thickness
            Composition and rank of coal
            Stratigraphy and structure
            Summary
29. Electric logsSP log
                    Normal and lateral logs
                    Focusing-electrode and induction
                        logs
                    Discussion of electric logs
30. SP log
31. Normal and lateral logs
32. Focusing-electrode and induction
                        logs
33. Discussion of electric logs
34. Gamma ray log
35. Density log
36. Neutron log
37. Acoustic velocity log
38. Measurement of the coal bed thickness
39. Composition and rank of coal
40. Stratigraphy and structure
41. Summary
42. Intended audience
43. References

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**ILLUSTRATIONS**

1. Format and
        classification of coal resources by reserves and
        subeconomic resources categories
2. Format and
        classification of coal resources by reserve and inferred
        reserve bases and subeconomic and inferred subeconomic
        resources categories
3. Flow chart
        showing hierarchy of coal resources and criteria for
        distinguishing resource categories
4. Diagram
        showing reliability categories based solely on distance
        from points of measurement
5. Coal fields
        of the conterminous United States
6. Coal fields
        of Alaska
7. Coal regions
        of the conterminous United States
8. Coal
        provinces of the conterminous United States
9. Determination
        of areas of reliability using coal thickness data only at
        points of measurement along outcrop line
10. Determination
        of areas of reliability from points of measurement on the
        outcrop line, supplemented by mine and drill-hole data
11. Determination
        of areas of reliability using coal thickness measurements
        taken along a continuously exposed, strip-mined bed,
        supplemented by drill-hole data
12. Determination
        of minimum thickness isoline
13. Determination
        of areas of reliability and overburden thickness
14. A ridge
        with construction of 14-inch minimum thickness limit
15. Same ridge
        as figure 14 with areas of reliability, coal thickness
        isopachs, and overburden contour
16. A simple
        valley reentrant with construction of 14-inch minimum
        thickness limit
17. Areas of
        reliability, overburden contours, and coal thickness
        isopachs to accompany figure 16.
18. A valley
        and ridge with part of coal bed less than minimum
        thickness but within determined 14-inch limit as
        illustrated in figure 16
19. Areas of
        reliability, overburden contours, and coal thickness
        isopachs to accompany figure 18
20. Coal
        categories in plane of coal bed, a structure section, and
        coal categories as viewed projected to the ground surface
        from plane of coal bed
21. Areas of
        resource categories for a flatlying coal bed based on
        data only from underground mined areas and drill holes
22. A small
        coal basin divided into areas of coal resource categories
23. A large,
        simple coal basin divided into areas of coal resource
        categories
24. Suggested
        form for recording coal resource data and calculated
        tonnage estimates
25. Suggested
        format for tabulating data and calculating tonnages
26. Early
        conventional electric log (1957) of the Owanah Kendrick
        No. 1 well, Big Horn County, Montana
27. Induction
        and conductivity geophysical logs (1960) of the
        Hose-Austin Drilling Company from Bone Brothers No. 1
        well, Rosebud County, Montana
28. Examples of
        oil- and gas-well geophysical logs from western Kentucky
        that can be used for coal bed correlations and coal
        resource evaluations
29. SP, gamma
        ray, acoustic velocity, normal resistivity, and induction
        conductivity logs (1971) from Davis Oil Grady Fed No. 1-2
        well, Sweetwater County, Wyoming
30. SP, gamma
        ray, density, dual induction-lateral log, and neutron
        logs (1978) from Getty Tri-County No. 1 well, Rosebud
        County, Montana
31. Five
        geophysical logs of a coal exploration drill hole showing
        response to coal and limestone

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**TABLES**

1. Classification of
        coals by rank
2. Average specific
        gravity and average weight of unbroken coal per unit
        volume of different ranks
3. Summary of coal
        resource criteria
4. Areas of reliability
        from figure 13 listed by overburden and coal thickness
        categories, and by counties
5. Areas of reliability
        from figure 15 listed in proper overburden and coal
        thickness categories
6. Areas of resource
        categories from figure 17 listed in proper reliability
        and thickness of coal and overburden categories
7. Areas of resource
        categories from figure 19 listed in proper reliability
        and thickness of coal and overburden categories

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