Blue Ridge VMS deposits

Region East, Southeast
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Volcanic and stratified massive sulfides occur in many locations throughout the complexly deformed metavolcanic and metasedimentary rocks of the eastern Blue Ridge, Virginia, North Carolina, South Carolina, Georgia, and Alabama. Many locations were mined extensively, for example, Gossan-Lead district, Virginia, and Ore Knob, North Carolina. Many other deposits vary from past producer to prospects to undiscovered. This focus area includes several Late Neoproterozoic to Early Paleozoic metavolcanic and metasedimentary rocks of the eastern Blue Ridge accretionary complex and associated terranes. Massive sulfides are hosted in the Nacoochee Formation schist and amphibolite of the Helen Group in the Dahlonega gold belt in the Chestatee mine in Lumptin County, Georgia. Other possible massive sulfide deposits are associated with Ordovician volcanic rocks in the belt. Polygon based on Hibbard and others (2006); Alabama polygons based on Osborne and others (1989): North Carolina and Virginia polygons for units in the Ashe Formation and based on North Carolina Geological Survey (1985) and Virginia Division of Mineral Resources (1993), respectively.
Identified resources Historical production of copper, iron, sulfur and zinc.
Production Combined amounts of past production and remaining sulfide within 150 to 300 m of the surface in the Gossan-Lead district have been estimated at 20 million tons. However, the volume of sulfide within 500 m of the surface may be 5 times to as much as 10 times greater than this (Gair and Slack, 1984). The Ore Knob mine was first worked for Fe, but the wrought iron forged from the ore contained too much Cu and S, so production at the mine was shifted to Cu.
Status Past mining. Most mine and prospects are abandoned; Ore Knob is a superfund site. Active exploration.
Estimated resources Ore Knob (1944): In-situ 30,000 mt @ 2% Cu, 105.7 g/mt Ag, 12.16 g/mt Au, and 0.05% Co.
Geologic maps Hibbard and others (2006), scale 1;500,000; North Carolina Geological Survey (1985), scale 1:500,000; Nelson and others (1998), scale 1:250,000; Nelson (1991, 1992), scale 1:24,000; Hadley and Nelson (1971), scale 1:250,000; Rankin and others (1972), scale 1:250,000; Espenshade and others (1975), scale 1:259,999; Nelson and others (1998), scale, 1:250,000; Higgins and others (2003), scale 1:100,000; Stose and Stose (1957), scale 1:62,500; Osborne and others (1989), scale 1:250,000; Beg (1987, 1988), scale 1:126,720; Dean and Clarke (1988), scale 1:126,720; Neathery (1977), scale 1:126,720; Neathery and Szabo (1974), scale 1:126,720; Reynolds and Neathery (1982), scale 1:1216,720; Rheams (1986), scale 1:126,720; Wade (1985), scale 1:126,720; Neathery and Reynolds (1975), scale 1:24,000.
Geophysical data Inadequate Rank 4 aeromagnetic and aeroradiometric coverage over much of the area. Rank 1 geophysics to be collected over the Alabama Blue Ridge and Piedmont (proposed FY22 funding).
Favorable rocks and structures Massive sulfides hosted by metavolcanic and metasedimentary rocks of the Ashe Metamorphic Suite (Formation), Wills Ridge Formation, and Lynchburg Formation and equivalents. Neoproterozoic to Lower Paleozoic Au- and sulfide-bearing mafic rocks and associated quartz veins within the western Blue Ridge (such as the Hillabee Greenstone), eastern Blue Ridge (for example, Mitchell Dam Amphibolite, Ketchepedrakee Amphibolite, and Beaverdam Amphibolite), and Inner Piedmont (for example., Waresville Schist and Ropes Creek Amphibolite) terranes (see Neathery, 1975; Whittington, 1982; Stow and others, 1984; Neilson and Stow, 1986).
Deposits Virginia: Gossan-Lead district (MRDS dep_id: 10307220), including Better Baker, Copperas Hill, Iron Ridge, Howard-Huey-Bumbarger; North Carolina: Ore Knob mine (MRDS dep_id: 10150868); Georgia: Jenny Stone prospect (MRDS dep_id: 10067498), Little Bob mine, Tallapoosa; Alabama: Pyriton area (MRDS dep_id: 10136009), Stone Hill.
Evidence from mineral occurrences MRDS; Feiss and Slack (1989); Mosier and others (2009); Geological Survey of Alabama's FY19 NGGDPP-Priority 3 critical minerals database.
Geochemical evidence Reported average compositions of amphibolite from the Alabama Piedmont indicate: Mitchell Dam Amphibolite: 62 ppm Ba, 39 ppm Co, 283 ppm Cr, 81 ppm Cu, 19 ppm Li, 142 ppm Ni, 1 ppm Pb, 207 ppm Sr, 221 ppm V, and 86 ppm Zn; Ketchepedrakee Amphibolite: 0 ppm Ba, 40 ppm Co, 338 ppm Cr, 63 ppm Cu, 18 ppm Li, 109 ppm Ni, 19 ppm Pb, 163 ppm Sr, 252 ppm V, and 88 ppm Zn; Beaverdam Amphibolite: 0 ppm Ba, 37 ppm Co, 301 ppm Cr, 113 ppm Cu, 10 ppm Li, 96 ppm Li, 0 ppm Pb, 189 ppm Sr, 270 ppm V, and 114 ppm Zn; Waresville Schist: 0 ppm Ba, 37 ppm Co, 248 ppm Cr, 49 ppm Cu, 8 ppm Li, 77 ppm Ni, 0 ppm Pb, 271 ppm Sr, 288 ppm V, and 83 ppm Zn; Ropes Creek Amphibolite: 36 ppm Ba, 39 ppm Co, 248 ppm Cr, 72 ppm Cu, 15 ppm Li, 78 ppm Ni, 0 ppm Pb, 183 ppm Sr, 316 ppm V, and 99 ppm Zn (Stow and others, 1984). Mines in the Gossan-Lead district, Virginia, reported to average 0.5% Cu, 0.1% Pb, 2% Zn.
Geophysical evidence Anomaly associated with mafic rocks (amphibolite).
Evidence from other sources Geologic mapping.
Comments This includes a large area where there is potential for other massive sulfide deposits associated with mafic meta-volcanic rocks in the eastern Blue Ridge. Volcanogenic massive sulfide deposits in Alabama's eastern Blue Ridge equivalents will be covered by FY 2022 Earth MRI aeromagnetic survey. Geophysical data are likely to be helpful in determining the extent of the source rocks. Geochemical analyses likely to be very helpful. Some EDMAP bedrock geologic mapping of focus area already available. Identified Cr-, Co-, Li-, Ni-, Sr-, V-, and Zn-bearing mafic rocks in the Alabama. Piedmont terranes include the Mitchell Dam Amphibolite, Ketchepedrakee Amphibolite, Beaverdam Amphibolite, Waresville Schist, and Ropes Creek Amphibolite. The mafic rocks of the Alabama Piedmont have never been mined for their critical mineral resources. There are few modern chemical analyses of polymetallic sulfide deposits in the Gossan-Lead district in Virginia, which has enormous resource potential. Native Bi, arsenopyrite, ilmenite, and rutile are commonly noted in the sulfide mineralogy.
Cover thickness and description Cover less than 10 m. Gossan at Ore Knob is 12-18 m thick.
Authors Arthur J. Merschat, Nora K. Foley, Bernard E. Hubbard, Dane S. VanDervoort, Elizabeth M. Bollen, John P. Whitmore, William L. Lassetter.
New data needs Geologic mapping, geochemistry and geophysics.
Geologic mapping and modeling needs Detailed geologic mapping of various mafic bodies. Geologic mapping, sampling, and analyses of mafic metavolcanic rocks and mica gneisses and schists to determine extent and distribution of metals.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage. Aeromagnetic data expected to image mafic rocks and associated structures, radiometric data can help with geologic mapping in vegetated terrane; alteration may be imaged. Electromagnetic methods may help image sulfides.
Digital elevation data needs Lidar coverage is fairly complete with QL1, Ql2, or QL3.