REEY CONTENT OF SHALES, FIRECLAYS, CARBONATE NODULES, AND TONSTEINS ASSOCIATED WITH PENNSYLVANIAN AGED COAL BEDS IN WESTERN WEST VIRGINIA: POTENTIAL SOURCES

Rare Earth Elements and Yttrium (REEY) are considered among the “critical minerals” due to their economic importance to high tech industries. Shales, fireclays, and coal ash have been identified as potential sources for REEY extraction. The high concentration of REEY in such rocks has been attributed to either enrichment through fluid flow and adsorption onto the clay mineral surfaces, or original enrichment in detrital monazite and xenotime during deposition.

Fifty-six samples from 15 outcrops of Pennsylvanian aged shales, fireclays, siderite nodules, and tonsteins associated with coals in southwestern West Virginia were analyzed for trace and REEY using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). For 3 of the samples from the middle Kanawha, the clay fraction was separated, fused with flux, dissolved, and analyzed for REEY. Samples with high REEY values (>300 ppm) were then examined using a Scanning Electron Microscope (SEM) with an energy dispersive spectrometer (EDS) to identify the minerals hosting REEY and their textural relations.

The results show that the highest ΣREEY contents were recorded for the Freeport and Lower Kittanning members (370-430 ppm), Kanawha (448 ppm), and the Pittsburgh coal seam (279-360 ppm). Siderite nodules within shale, and silty samples from the Dingess and Crummies Shale of the Lower Kanawha formation also record high values (> 400 ppm REEY). The clay fractions separated from two siderite nodules and one shale showed lower concentrations of REEY (250-350 ppm). All samples were light rare earth element – enriched. Back scatter imaging and EDS analysis for samples with REEY > 400 ppm showed a significant amount of detrital grains of monazite, xenotime (and zircon), whereas the common clay minerals (kaolinite and illite) did not contain any REEY. On the other hand, a tonstein sample had no detrital monazite or xenotime. These results suggest that although some REEYs may have been transported by fluid as evidenced by the high REEY contents of the siderite nodules, most of the REEY enrichment is due to a high modal content of detrital monazite and xenotime in shales and siltstones.