On a Unified Core Characterization Methodology to Support the Systematic Assessment of Rare Earth Elements and Critical Minerals Bearing Unconventional Carbon Ores and Sedimentary Strata

Abstract

A significant gap exists in our understanding and ability to predict the spatial occurrence and extent of rare earth elements (REE) and certain critical minerals (CM) in sedimentary strata. This is largely due to a lack of existing, systematic, and well-distributed REE and CM samples and analyses in United States sedimentary basins. In addition, the type of sampling and characterization performed to date has generally lacked the resolution and approach required to constrain geologic and geographic heterogeneities typical of subsurface, mineral resources. Here, we describe a robust and systematic method for collecting core scale characterization data that can be applied to studies on the contextual and spatial attributes, the geologic history, and lithostratigraphy of sedimentary basins. The methods were developed using drilled cores from coal bearing sedimentary strata in the Powder River Basin, Wyoming (PRB). The goal of this effort is to create a unified core characterization methodology to guide systematic collection of key data to achieve a foundation of spatially and geologically constrained REEs and CMs. This guidance covers a range of measurement types and methods that are each useful either individually or in combination to support characterization and delineation of REE and CM occurrences. The methods herein, whether used in part or in full, establish a framework to guide consistent acquisition of geological, geochemical, and geospatial datasets that are key to assessing and validating REE and CM occurrences from geologic sources to support future exploration, assessment, and techno-economic related models and analyses.

A Geo-Data Science Method for Assessing Unconventional Rare-Earth Element Resources in Sedimentary Systems

“…Future scenarios in which sufficient data and information are available could support quantitative estimates of resources using the URC assessment method, primarily at the mine or seam scale, depending upon the data qualities. Key to this effort would be core data characterizing not only the vertical and lateral distribution of REEs, but also host rock mineral phases, geochemical composition, and lithostratigraphy to develop paragenetic relationships and identify potential enrichment mechanisms (Montross et al, 2022). Adequate and consistent spatial coverage and sampling resolution of cores would also be required to minimize the influence of sampling bias and ensure recording of small-scale variations.…”

“…where C m is the confidence for mechanism m, PE m is the PE score for mechanism m, LaCeY xi are the geochemical concentrations for La, Ce, and Y for a single coal sample, LaCeY x are the geochemical concentrations for La, Ce, and Y for all coal samples within the study area. The sum of La, Ce, and Y concentrations is used as a proxy for total REEs given the analogous geochemical behavior (Montross et al, 2022) and the fact that many samples lack measurements for total REEs. The confidence metric outputs range from zero to one, which translates as low to high confidence in PE scores, respectively.…”

Rare-Earth Element Phase Associations in Four West Virginia Coal Samples

“…Scanning electron microscopy-energy-dispersive X-ray spectroscopy: Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) were used to identify REY-bearing mineral phases in representative coal sample chips. The analysis was performed following the methods outlined in Montross et al [29] and is briefly summarized below. Portable X-ray fluorescence (pXRF) was used as a screening tool to identify the most promising sample chips for SEM-EDS.…”

“…The element concentrations determined by pXRF are shown in Table 3. Although pXRF measurements of trace elements may not be highly accurate, the relative concentrations can be used to select the most promising REY-bearing samples for SEM-EDS analysis [29]. Rare-earth element bearing minerals identified using SEM-EDS are described in Table 4.…”