Data Analysis of the Enrichment of Rare Earth Elements in Illinois Basin Coal Seams

Author

Ian Wilson Bennett, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2025

Degree Name

Master of Science

Department

Geology

First Advisor

Lefticariu, Liliana

Second Advisor

Elrick, Scott

Third Advisor

Hummer, Daniel

Abstract

As the United States attempts to move away from using foreign sources of rare earth elements (REEs), it is crucial to find domestic sources to aid with this transition. New, unconventional sources of these elements that yield high enough amounts to make said sources economically viable to mine are sought after. Several recent projects from the Department of Energy have examined coal and coal by-products from U.S. coal basins as an unconventional source for these elements. One group of projects has focused on the geochemical characteristics of the Illinois Basin coal seams.

However, these projects do not answer how enriched the REEs are, nor if other elements found alongside them are enriched as well. To find this out, multiple datasets were acquired from the Illinois State Geological Survey (ISGS). These datasets, each comprising of a multitude of coal samples and the various attributes they were originally tested for, were arranged and structured based on their coal seam and the ISGS-defined region of the Illinois Basin. The data analysis consists of determining enrichments compared to the coal’s Clarke values and the values of the Upper Continental Crust (UCC), and the statistical analysis of the correlations that could be identified among oxides, potential hydrothermal elements, and REEs. These results were then inserted into heatmaps and box plots, and analyzed to determine the concentration of the elements and their enrichment, what minerals are potentially present in the basin’s coal, and how the chemical index of alteration varied throughout the seams and regions, all to give a better understanding of the REEs’ distribution and the relationships that they possess among the elemental and mineralogical matter that is found in the Illinois Basin.

These results show that there is a slight enrichment of REEs in the Illinois Basin’s coal, as compared to their Clarke values. The significant positive correlations between the oxides of Al2O3, SiO2, and TiO2, and the REEs can be used to suggest a possible terrigenous enrichment for the REEs, but there are uncertainties due to differing enrichment calculations. There are also enrichments in nickel, zinc, and lead, as compared to their Clarke values, which can be used to suggest hydrothermal enrichments. However, because there were few significant positive correlations between the hydrothermal elements and the REEs, it can be said that these fluids did not contribute to the overall enrichment of the REEs. Additionally, by further analysis the relationships found in the data, it can be concluded that a wide range of minerals, such as quartz, calcite, rutile, pyrite, sphalerite, galena, and REE-baring minerals such as monazite and xenotime, are present throughout the coal found in the basin. However, numerous limitations, such as the absence of several pieces of data from one of the datasets used, an unequal sample distribution among the seams and regions tested, and uncertainty involving the overall impact outliers had on the data and the results, created multiple sets of issues that require the instillation of standardized methods that will help with processes and understanding similar sets of data better. But overall, these findings will help to further the understanding of the depositional conditions and processes that occurred in this region that has led to the coal found in the state of Illinois today.