| Basis for focus area |
Potential areas of interest are: 1) along the western edge of the Blue Ridge mountains where Mn mining in the United States was at its peak in the early 1900s (for example, Stose and others, 1919), and 2) in the central Shenandoah Valley where REE deposits may also occur in conjunction with the youngest known Eocene-age igneous intrusive rocks in the eastern United States. An aeromagnetic survey centered on Staunton, Virginia was conducted by the USGS in 1963 (Johnson and Watkins, 1963) and showed the presence of igneous dikes and plugs within the Shenandoah Valley, but did not cover the magmatic zone further north or west. This focus area also includes an area in eastern West Virginia outlined as permissive for undiscovered supergene Mn deposits (Cannon and Force, 1983). |
| Identified resources |
Identified resources and historical production of manganese from cobalt-bearing manganese veins, veinlets, and stringers in Cambro-Ordovician carbonate rocks of the Valley and Ridge. |
| Production |
Alabama: Reported 264 (short) tons of Mn ore produced in 1917 and 1,152 (short) tons of Mn ore produced in 1918 (Wingard, 1921); 40 (short) tons of Mn ore produced in 1919 and 58 (short) tons of Mn ore produced in 1920 (Wingard, 1922); 475 (short) tons of Mn ore produced in 1922 and at least 694 (short) tons of Mn ore produced in 1923 (Jones, 1925); 611 (short) tons of Mn ore produced in 1924 (Jones, 1926b); 938 (short) tons of Mn ore and 298 (short) tons of ferruginous Mn ore produced in 1925 and 896 (short) tons of Mn ore and 1,018 (short) tons of ferruginous Mn ore produced in 1926 (Barksdale, 1929); Virginia: Historical Mn production between 1867 and 1950 estimated to be about 378 thousand tons of ore grading >35% Mn, plus 164 thousand tons grading 10-35% Mn. |
| Status |
Past mining. |
| Estimated resources |
Unknown. |
| Geologic maps |
Carmichael and others (2017), scale 1:200,000; Johnson and Watkins (1963), scale 1:62,500; Stose and Miser (1922), scale 1:500,000; Osborne and others (1989), scale 1:500,000; Causey (1965a), scale 1:63,360; Reynolds and Neathery (1982), scale 1:126,720; Rheams (1990), scale 1:126,720. |
| Geophysical data |
Inadequate Rank 3 to 5 aeromagnetic and Rank 5 aeroradiometric coverage. |
| Favorable rocks and structures |
Alabama: Cobalt-bearing manganese veins/veinlets within Cambrian and/or Ordovician carbonate rocks, with secondary concentration in overlying residuum; see for example, Gibson (1893); Rheams (1992). Virginia Eastern belt: lower contact of Cambrian-age Shady Dolomite with underlying Erwin Formation; Virginia Western belt: lower Devonian Oriskany Formation and Helderburg Formation. |
| Deposits |
Districts include at least 43 mines and 83 prospects. Tennessee: Shady Valley district, Mountain City district, Butler district, Stony Creek district, Hampton district, Unicoi district, Embreeville and Bumpass Cove districts; Virginia: Mineral Ridge, Strange mine, Arms mine, Round Mountain mine. |
| Evidence from mineral occurrences |
MRDS; Rheams (1992); Geological Survey of Alabama's FY19 NGGDPP-Priority 3 critical minerals database. |
| Geochemical evidence |
Several Mn deposits in Alabama have between 1.59 to 4.84% Co: see Reynolds and Neathery (1982), Rheams (1990), Rheams (1992). |
| Geophysical evidence |
Inadequate aeromagnetic and aeroradiometric data (aeromagnetic data rank 4; radiometric rank 5), but useful for geologic framework and to help identify the extent/distribution of cobalt- and manganese-bearing source rocks. |
| Evidence from other sources |
Geologic mapping. |
| Comments |
Study area overlaps with FEDMAP and STATEMAP projects. A recent investigation (Carmichael and others, 2017) suggested that these elements may have been emplaced by hypogene hydrothermal fluids along zones of structural weakness, and later concentrated by supergene weathering processes. Veins may be hydrothermal or supergene, or a hybrid of both. Vein cement has undergone mineralogical changes. Vein ages indicate that there is coincidence with igneous occurrences and possibly the Chesapeake impact event. Carbonates can be juxtaposed against quartz-rich sandstones. There is evidence of faulting (breccias) in a zone between Woodstock and Harrisonburg, Virginia. Ore-bearing units may be along strike of lower economic potential than mines. New USGS mapping is currently being done in areas (for example, Shenandoah Valley area) that were mined for Mn in the past. Ananja Shah (USGS) states that aeromagnetic data could be helpful for "indirect" delineation of mafic volcanic units associated with Mn mineralization. Virginia Energy (formerly the Virginia Department of Mines, Minerals and Energy) are working and collaborating with USGS mapping work in the area. Alabama Geological Survey may want geochemistry for this deposit type in that state. Manganese is mobile in reduced settings and breccias may contain primary phases or preliminary phases. Manganese also can reprecipitate as nodules. Veins with K-bearing minerals can be rich in Co (up to 100s of ppm), Be, some REE and can occur in the Valley and Ridge area from New York to Alabama, and in Virginia, Tennessee, and North Carolina. |
| Cover thickness and description |
Exposed bedrock to thin cover. |
| Authors |
Arthur J. Merschat, Bernard E. Hubbard, John P. Whitmore, Dane S. VanDervoort, Peter J. Lemiszki. |
| New data needs |
Geophysical data, geologic mapping, and geochemical analyses. Only 5 out of 26 7.5-minute (scale 1:24,000) geologic quadrangle maps have been completed for this area in Alabama. |
| Geologic mapping and modeling needs |
The Geological Survey of Alabama has published detailed mapping for much of the Valley and Ridge province as a result of the STATEMAP program; however, geochemical analyses are needed in order to assess the quality and economic potential of the cobalt-bearing manganese deposits. |
| Geophysical survey and modeling needs |
New high resolution geophysical surveys may help locate manganese oxide deposits that host the Co and mafic dikes across the Valley and Ridge, which might have unrecognized economic potential. |
| Digital elevation data needs |
Full QL2 lidar is available for portions covering the states of Alabama, Tennessee, North Carolina and Pennsylvania. Nearly complete coverage in Virginia except for the South-central portion of the state No lidar coverage within portions covering Georgia. |
