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Author ORCID Identifier

[https://orcid.org/0009-0007-1217-0241]

Date Available

5-16-2026

Year of Publication

2026

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College

Arts and Sciences

Department/School/Program

Earth and Environmental Sciences (Geology)

Faculty

Georgina Lukoczki

Faculty

Andrea Erhardt

Abstract

Critical minerals are vital to the United States economy and national security, yet their supply chains are at risk. Common minerals in Mississippi Valley-type (MVT) deposits, such as sphalerite, galena, fluorite, and barite, host critical metals such as barium, gallium, germanium, and zinc, which are essential for energy technologies. An investigation of three MVT mineral districts in Kentucky elucidated previously unrecognized systematics, genetic relationships, and sources of ore components using stable and radiogenic isotope geochemistry, particularly from galena, sphalerite, barite, and gangue minerals (e.g., carbonates). The localization and dominant type of mineralization in each district are potentially influenced by deep crustal magnetic boundaries that occur in the vicinity of these three mineral districts. These deep crustal boundaries may act as conduits for mineralizing fluids and have a more significant influence on MVT mineralization than previously recognized.

Sulfur isotope data of sulfide and barite samples from the Kentucky-Tennessee Mineral District (KTMD), Central Kentucky Mineral District (CKMD), and Illinois-Kentucky Fluorspar District (IKFD) show overlapping values, indicating that sulfur brought to these districts mostly originated from evaporite minerals hosted in shallower strata. In the CKMD and KTMD, bacterial, whereas in the IKFD thermochemical sulfate reduction reactions acted as the primary process that reduced the sulfates to sulfides, which then mixed and interacted with metal-bearing fluids to precipitate out sulfide minerals. Sulfates that were unaffected by these processes interacted with the metal-bearing fluids and precipitated sulfate minerals.

Comparisons of lead (Pb) isotope ratios against distance from the nearest deep crustal boundary show a moderate correlation, with more radiogenic Pb closer to the boundaries, suggesting a stronger input of radiogenic Pb from Precambrian carried by basement-derived fluids. Similar comparisons with gallium (Ga) and germanium (Ge) abundance indicate that a larger concentration of these metals occur in minerals farther away from the boundaries suggesting that most Ga and Ge were leached from basin shales and delivered to the site of mineralization by basin brines. Strontium (Sr) isotope ratios from the three mineral districts did not reveal a spatial relationship with the deep crustal boundaries and show that most Sr likely originated either from a seawater-derived source, with contributions of more radiogenic Sr originating from Precambrian basement rocks or Sr-rich clays and minerals. Overall, isotope analyses showed that basement-derived fluids likely used deep crustal boundaries as conduits, influencing the localization and migration of MVT mineralizing fluids. This suggest that deep crustal boundaries may exist as a useful proxy for finding undiscovered MVT deposits across the United States.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2026.190

Archival?

Archival

Funding Information

Funded by the United States Geological Survey (Earth Mapping Resource Initiative Program) 2024–2026: This grant supported work as a research assistant, lab expenses for stable and radiogenic isotope work, and travel.

Travel grant, Geological Society of America: This grant supported travel to Memphis, Tennessee to present this research.

Travel grant, Brown-McFarland Fun: This grant supported travel to Memphis, Tennessee to present this research.

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