Published proximate analyses, heat values, and sulfur contents of representative Wyoming coals were compared by sample types (face, tipple, and delivered) and by mining methods (underground and strip). These comparisons suggest that the quality of thick, potentially strippable Wyoming coals should not be characterized too stringently from published proximate analyses and heat values without consideration of detailed background information on each analysis. Minimally, the type of sample, date of analysis, sizes sampled, description of coal, thickness and part of coal sampled and/or discarded, type of mine, mining equipment, preparation facility, processing, and even customer identification should be known.

This precaution is deemed necessary for the following reasons.

1. Although analyses of face samples best characterize a coal bed in its natural state, most published analyses of Wyoming coals are either very old face samples from abandoned underground mines or they are tipple and delivered samples.

2. Most available face, tipple, and delivered samples of thick coals (35-118 ft thick) are only representative of one fourth to one half of the entire thickness of such beds.

3. For a given coal bed, there are not enough surface mines for which analyses are available to characterize

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reliably the quality of strippable reserves.

4. For a given coal bed, tipple and delivered samples from strip mines tend to exhibit lower average moisture contents (as-received basis), higher average ash contents (dry basis), as well as greater ranges in ash contents, and less predictable average heat values (dry basis) than expected.

5. Although for many coals tipple and delivered samples are available from both surface and deep mines, analyses of these types of samples are so dependent on the type and use of mining equipment, preparation facilities, processing, and contract specifications that they may only by chance bear a close resemblance to the coal in its natural state.

Apparently only a coal's sulfur content can be characterized accurately from existing published analyses of face, tipple, or delivered samples, as no significant differences were noted in any of the comparisons.

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