Report of Investigations--KGS


Bench samples of the Fire Clay coal bed, collected from 28 localities in a study area of eight 7.5-minute quadrangles in the Eastern Kentucky Coal Field, were analyzed geochemically, petrographically, and palynologically to determine any spatial or temporal trends among the studied parameters.

At most sample sites the Fire Clay is split by a flint-clay parting of probable volcanic origin. The upper bench of the Fire Clay coal generally is thick, laterally continuous, low in ash yield and sulfur content, has a moderate to high calorific value, and is high in total vitrinite content. In contrast, the lower bench generally is thin, laterally discontinuous, moderate to high in ash yield and sulfur content, has a low to moderate calorific value, and has high liptinite and inertinite contents. Rider coals, present at two sample sites, are thin, laterally discontinuous, and high in both ash yield and sulfur content.

Fire Clay coal extracted from underground mines typically contains roof and floor rock, which is separated by conventional coal-cleaning methods. The analytical data were grouped into categories of increasing coal purity to approximate a cleaned coal product. Results indicate that some parameters (Btu and total vitrinite content) increase along a trend from higher ash to lower ash coal. Other parameters (ash yield, total sulfur content, and several minor elements) decrease. Still others (thickness and total moisture) show no trend at all. A comparison of these data with previously accumulated data from 64 cleaned coal samples (collected from preparation plants) confirms these trends. This is significant, especially with regard to Titles III and IV of the Clean Air Act Amendments of 1990, in that many deleterious components of coal appear to be removable by conventional coal-cleaning methods prior to combustion in an industrial furnace. Examples of these undesirable constituents include pyrite, chromium, cobalt, and nickel.

The Fire Clay coal was grouped into four compositional categories for paleoecological interpretation. The categories are (1) a Lycospora-dominant group with high vitrinite contents that is interpreted to have formed in areas of the Fire Clay paleomire that were kept very wet, to the point of having standing water, a majority of the time (this group probably developed in areas of the mire that were dominantly rheotrophic and planar); (2) a mixed-palynoflora group with high vitrinite contents that is defined by having a more diverse palynoflora than the first group (increased percentages of small lycopsid, fern, and calamite spores), and high percentages of vitrinite (this group is also interpreted to have formed in areas that were very wet most of the time, and were predominantly rheotrophic and planar); (3) a mixed-palynoflora group with moderate to low vitrinite contents that contains increased percentages of inertinite compared to the first two groups and a diverse palynoflora, possibly because the mire became more ombrotrophic and domed; and (4) a mixed-palynoflora group with high ash yield whose palynoflora is marked by various mixtures of lycopsids (trees and small forms), ferns (tree-like and small forms), calamites, and cordaite spores; samples defined by this group contain elevated percentages of liptinite and inertinite macerals, as well as higher ash yields. The conditions under which group 4 formed probably were rheotrophic and planar. Group 4 defines all the samples in the lower bench of the Fire Clay coal bed.

Publication Date



Series XI

Report Number

Report of Investigations 14

Digital Object Identifier (DOI)


© 1999 Kentucky Geological Survey, University of Kentucky