Coal Distribution and Resources

Coal deposits are broadly categorized into resources and reserves. Resources refer to the quantity of coal that may be present in a deposit or coalfield but may not take into account the feasibility of mining the coal economically. Reserves generally tend to be classified as proven or measured and probable or indicated, depending on the level of exploration of the coalfield. The basis for computing resources and reserves varies between countries, which makes it difficult for direct comparisons. Walker [5] discusses the various measurement criteria used by the major coal-producing countries in the world in detail. Figure 1-5 illustrates the relationship between resources and reserves in the United States as of January 1, 1997 [16]. The United States has a total of nearly 4000 billion short tons of coal resources, with approximately 19 billion short tons classified as recoverable reserves at active mines out of 275 billion short tons that are economically recoverable.

The various categories shown in Figure 1-5 are defined as:

• Total resources—Coal that can currently, or potentially may, be extracted economically;

• Measured resources—Quantity of coal that has been determined to a high degree of geologic assurance;

• Indicated resources—Quantity of coal that has been determined to a moderate degree of geological assurance;

FIGURE 1-5. United States coal resources and reserves in billion short tons. (From EIA, U.S. Coal Reserves: 1997 Update, U.S. Department of Energy, Energy Information Administration, Washington, D.C., February 1999, p. 5, Appendix A.)

Depths and Thickness)

Identified Resources (Measured, Indicated, and Inferred)

Total Resources (Identified and Undiscovered)

FIGURE 1-5. United States coal resources and reserves in billion short tons. (From EIA, U.S. Coal Reserves: 1997 Update, U.S. Department of Energy, Energy Information Administration, Washington, D.C., February 1999, p. 5, Appendix A.)

• Inferred resources—Quantity of coal that has been determined with a low degree of geologic assurance;

• Recoverable reserves—Coal that can be recovered economically with technology currently available or in the foreseeable future.

Terminology also varies among countries and can contribute to confusion when comparing coal resources and reserves. For purposes of discussion in this chapter and to lessen confusion, recoverable coal reserves will primarily be used when comparing world coal deposits.

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