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Igneous characterization and geologic hydrogen implications from the Serpentine deposit, Duluth Complex, Minnesota, U.S.A., integrating continuous XRF core scanning and automated mineralogy
Pelren, Joseph Fisher
Pelren, Joseph Fisher
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2025
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Abstract
This study presents a novel, data-driven workflow for assessing subsurface mineralogical characteristics relevant to geologic hydrogen generation, using drill core from the Serpentine Deposit within the Duluth Complex, a large mafic to ultramafic layered intrusion in northeastern Minnesota. With growing interest in geologic hydrogen as a clean energy resource, there is increasing need for methodologies that can efficiently identify hydrogen-generating lithologies through detailed mineralogical and geochemical analysis. While current methods allow for fast and affordable measurements of downhole drill core geochemistry, there does not yet exist an analytical tool that can produce mineralogical data with comparable efficiency.
Approximately 2,000 meters of drill core were analyzed using high-resolution, continuous X-ray fluorescence (XRF) core scanning. These data were paired with targeted sub-sample analysis performed using scanning electron microscopy-based automated mineralogy and electron probe microanalysis (EPMA), enabling the derivation of mineral modes and mineral chemistry downhole. A new software tool applied bounded-variable least-squares regression to transform bulk geochemical data into interval-specific normative mineral assemblages.
Key variables relevant to hydrogen production—such as olivine and plagioclase modal abundances, bulk nickel concentration, and olivine composition—were extracted and used to generate continuous downhole profiles of hydrogen potential. The results highlight several intervals with favorable lithologies, characterized by plagioclase content below 35 vol.% and olivine content above 40 vol.%. These include dunites, peridotites, and select olivine-rich pyroxenites. Olivine compositions were further classified into fayalitic (Fo₆₀–Fo₀) and magnesian (Fo₉₀–Fo₇₀) types, corresponding to zones with low- and high-temperature hydrogen generation potential, respectively.
This study demonstrates that integrating geochemical scanning with mineralogical and mineral chemical data provides a robust framework for identifying hydrogen-favorable zones in ultramafic rocks. The resulting continuous profiles offer a powerful tool for advancing exploration strategies in geologic hydrogen and can be applied more broadly to subsurface resource assessments requiring high-resolution mineralogical insight.
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