Author ORCID Identifier:
Date of Graduation
7-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Geosciences (PhD)
Degree Level
Graduate
Department
Geosciences
Advisor/Mentor
Potra, Adriana
Committee Member
Dumond, Gregory
Second Committee Member
Samuelsen, John
Third Committee Member
Hays, Phillip
Fourth Committee Member
McGilvery, Thomas (Mac)
Keywords
Clumped isotopes; Lead isotopes; Mississippi Valley-type (MVT) deposits; Sequential chemical separation; Shale
Abstract
The linear Pb isotope trend defined by Mississippi Valley-type (MVT) Pb–Zn deposits in the US midcontinent has been conventionally interpreted as evidence of mixing between discrete crustal Pb sources, including shale. However, the role of shale as metal reservoirs has been difficult to evaluate due to possible dilution of isotopically distinct organic and inorganic phases by the whole-rock isotope signature. This study develops a sequential chemical separation method that isolates bitumen, kerogen concentrate, and inorganic fractions from shale for independent Pb isotope analysis. Separated fractions carry systematically different, isotope signatures masked in bulk-rock data. Applied across shales of varying age, maturity, and organic/metal content from the Forest City-Cherokee, Ouachita, and Ozark regions, this approach shows that shale Pb isotope composition evolves predictably with thermal maturation. The Pb isotope signature of a few shale fractions overlap or approach those of the Ozark MVT ores, suggesting that the ore isotope trend could be explained, at least in part, as progressive Pb release during shale maturation. A complementary clumped-isotope (Δ47) study of ore-related carbonates across six MVT districts provides the first multi-district, fluid-independent temperature constraints on these deposits, showing hot (~107–173 °C), 18O-enriched brines during main-stage mineralization, followed by cooling and meteoric dilution during late-stage calcite formation. Overall, these results support shale as a potential source for MVT mineralization and link their maturation history to the thermal and hydrologic evolution of the basinal fluids that formed the ores.
Citation
Herath, H. K. (2026). A Multi-Proxy Geochemical Investigation of the Mississippi Valley-Type Mineralization in the U.S Midcontinent: Constraints on Metal Sources and Thermal Evolution of the Ore-Forming Fluids. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6396
