New Insight Into The Origin Of Manganese Oxide Ore Deposits In The Appalachian Valley And Ridge Of Northeastern Tennessee And Northern Virginia, USA

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Sarah K. Carmichael Ph.D., Assistant Professor of Geology (Creator)
Appalachian State University (ASU )
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Abstract: Manganese oxide deposits have long been observed in association with carbonates within the Appalachian Mountains, but their origin has remained enigmatic for well over a century. Ore deposits of Mn oxides from several productive sites located in eastern Tennessee and northern Virginia display morphologies that include botryoidal and branching forms, massive nodules, breccia matrix cements, and fracture fills. The primary ore minerals include hollandite, cryptomelane, and romanèchite. Samples of Mn oxides from multiple localities in these regions were analyzed using electron microscopy, X-ray analysis, Fourier transform infrared spectroscopy, and trace/rare earth element geochemistry. The samples from eastern Tennessee have biological morphologies, contain residual biopolymers, and exhibit REE signatures that suggest the ore formation was due to supergene enrichment (likely coupled with microbial activity). In contrast, several northern Virginia ores hosted within quartz-sandstone breccias exhibit petrographic relations, mineral morphologies, and REE signatures indicating inorganic precipitation, and a likely hydrothermal origin with supergene overprinting. Nodular accumulations of Mn oxides within weathered alluvial deposits that occur near to breccia-hosted Mn deposits in Virginia show geochemical signatures that are distinct from the breccia matrices, and appear to reflect remobilization of earlier-emplaced Mn and concentration within supergene traps. Based on the proximity of all of the productive ore deposits to mapped faults or other zones of deformation, we suggest that the primary source of all of the Mn may have been deep-seated, and that Mn oxides with supergene and/or biological characteristics result from the local remobilization and concentration of this primary Mn.

Additional Information

Carmichael, S. K., Doctor, D. H., Wilson, C. G., Feierstein, J., and McAleer, R. J., 2017, New insight into the origin of manganese oxide ore deposits in the Appalachian Valley and Ridge of northeastern Tennessee and northern Virginia, USA: Geological Society of America Bulletin 129 (9-10), p. 1158-1180. The copy of record is available from GSA Bulletin, Publisher version of record available at:
Language: English
Date: 2017
Appalachians, geochemistry, cryptomelane hollandite mineral deposits, genesis metal ores, manganese ores, manganese oxides, metals, oxides, Tennessee, Virginia, United States, North America, rare earth

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