GEOLOGIC MAPPING AND FIELD OBSERVATIONS OF THE MODE AND OCCURRENCE OF MN-OXIDE IN THE DOE RIDGE CULMINATION, MOUNTAIN CITY, TN

Manganese oxides, hydroxides, and oxyhydroxides (herein referred to as Mn-oxides) are commonly found as discrete and disseminated deposits below the middle Ordovician unconformity throughout the Valley and Ridge from GA to VA. While deposits have been mapped and locally mined, the exact relationship between Mn-oxides and associated structures, primarily thrust faults, is unknown. The purpose of this project was to conduct detailed geologic mapping (1:12,000) to confirm previous work by King and Ferguson (1960) and to elucidate the details of Mn-oxide occurrence. This research focuses on Neoproterozoic-Cambrian Erwin-Shady-Rome sequences that are folded and faulted to form the Doe Ridge Culmination southwest of Mountain City, TN. Our mapping confirms that Mn-oxide deposits are dominantly associated with brecciated jasperoid and residual clays of the Shady dolomite exposed in the hanging wall of northeast trending thrust faults and is juxtaposed atop Erwin Formation quartzites.

Mn-oxides primarily occur as matrix material and coatings on jasperoid breccia and as vug infillings, with minor occurrences crosscutting and parallel to preserved bedding planes. Mn-oxides exhibit a variety of morphologies: pellets, botryoidal nodules, dendrites, shrubs, drusy coatings, and laminae. Crosscutting relationships suggest that the Mn-oxides postdate formation of jasperoid breccia. Crystal structures and growth patterns also suggest a biological role in Mn-oxide formation. XRD, SEM, and TEM analyses show that Mn-oxide mineralogy is primarily romanechite and solid solutions of cryptomelane-hollandite . Additional outcrop-scale mapping coupled with Ar/Ar age dating of cryptomelane will enable paleoreconstruction of fluid flow pathways and better constrain the origin of Mn-rich ore fluids.