RARE EARTH ELEMENT VARIABILITY WITHIN THE FIRE CLAY COAL BED IN EASTERN KENTUCKY

Samples of the Fire Clay coal from exploration drill cores and active mines were examined geochemically to determine the amounts and variability of rare earth elements in the coal and associated rock strata. The Fire Clay is a significant coal resource in eastern Kentucky and is unique among central Appalachian coal beds in that it contains a distinctive flint-clay parting that represents an altered volcanic ash deposit. The flint-clay parting, which usually occurs in lower parts of the coal, effectively divides the coal into lower and upper benches. Whereas the lower bench varies in thickness and extent, the upper bench is more uniform in distribution.

The analyzed coal samples have an average total REYSc (i.e., the rare earth elements, yttrium and scandium) concentration of 1,447 ppm (ash basis); light rare earth elements and yttrium (REY, avg. 1,046 ppm, ash basis) are more abundant than heavy REY (avg. 350 ppm, ash basis). Associated rock samples, which include seat rock, roof rock, carbonaceous shale, and the flint-clay parting, collectively have an average REYSc concentration of 400 ppm (ash basis), with a similar bias toward light REY (light REY/heavy REY = 6.2). Among the different types of rock that were sampled and analyzed, roof-rock samples contained the least total REYSc (avg. 331 ppm, ash basis), followed by seat-rock samples (avg. 384.1 ppm, ash basis). Flint-clay and carbonaceous samples had average REYSc concentrations of 447 and 603 ppm (ash basis), respectively, and all lithologies were biased toward light REY.

The Fire Clay is low in ash (avg. 7.5 percent, dry basis) and sulfur (avg. 1.0 percent, dry basis), which enhances its value as a thermal coal for electricity generation. However, these low ash and sulfur values decrease the average REYSc concentration from 1,447 ppm (ash basis) to 109 ppm when considered on a whole-coal basis as the organic matter acts as a diluent. For this reason, rock lithologies that are mined with the coal, separated in coal-preparation plants and ultimately discarded, represent the principal REYSc resource in the Fire Clay coal. A volumetric analysis of two refuse areas from a preparation plant in the study area indicates the presence of more than 300 million cubic feet, or about 24 million tons, of refuse material that may have potential for future REYSc processing and recovery.