Explained by John F. Slack, Sandra H.B. Clark, John D. Peper, and Howard A. Pohn
On the choice of deposit models
No major sandstone-hosted lead-zinc deposits are known in the United States, and deposits of this type are of relatively minor economic importance by world standards. The only significant deposit in the United States was developed at the Goose Creek mine in the Indian Creek district of southeast Missouri (Kyle and Gutierrez, 1988). The importance of some deposits, such as the large (80 million metric tons) Laisvall lead-zinc deposit in northern Sweden, shows that potential must be considered for the occurrence of similar deposits in geologically analogous settings. Sandstone-hosted lead-zinc deposits are stratabound concentrations of galena and generally minor sphalerite that occur within quartz-rich sandstone and quartzite overlying feldspathic basement rocks (Rickard and others, 1979; Bjørlykke and Sangster, 1981). The origin of sandstone-hosted lead-zinc deposits by transport of metals through permeable channels to an environment with sufficiently high H2S content to precipitate sulfides from groundwater or basinal brines resembles that of sediment-hosted copper and Mississippi Valley deposits.
Clastic sedimentary sequences that occur near underlying basement rocks are potential hosts for lead-zinc deposits in which metals were concentrated by groundwater leaching from feldspar-rich basement rocks. Although no deposits are known in the United States Appalachians, several occurrences have been described from the Quebec Appalachians to the north (Schrijver and Beaudoin, 1987), suggesting potential for mineralization of the Cheshire Quartzite and correlative units of Early Cambrian age that overlie feldspathic basement rocks. Galena samples from the Rossie veins of western New York have lead isotope compositions and fluid inclusions (Ayuso and others, 1987) that are compatible with an origin from a Paleozoic basinal brine that migrated into fractures during tectonism. The migration of base-metals in brines suggests the possibility for the formation of sandstone-hosted lead-zinc deposits in favorable host rocks such as the Upper Cambrian Potsdam Sandstone that forms a basal unit overlying the Grenvillian basement of the Adirondacks.
For sandstone-hosted lead-zinc deposits that form as a result of the tectonically driven flow of metal-bearing brines, proximity to basement rocks may not be a critical factor, and all clastic sequences that were present at the time of the Alleghenian deformation are potential host rocks. An occurrence of this deposit type has been recognized in Silurian rocks of the Tuscarora Quartzite in southwestern Virginia (J.R. Craig, oral commun., 1980). This occurrence was discovered by A. Hayes during construction of the I-77 highway tunnel under Walker Mountain, 10 km north-northwest of Wytheville. Representative parts of the galena-cemented samples were given to J.E. Gair, USGS, by J.R., Craig in 1980. Ore samples from the Laisvall mine (see Rickard and others, 1979; Lindblom, 1986) collected by J.E. Gair and J.F. Slack in 1979, are nearly identical in texture and mineralogy to the samples collected by Hayes from the I-77 tunnel.
Other occurrences of lead or zinc in Silurian to Devonian sandstone or quartzite are known in Pennsylvania, Virginia, and West Virginia (Martens, 1964; Smith, 1977; Clark, 1987; Cannon and others, 1994), and sandstone hosts the galena-sphalerite veins of the Shawangunk district of New York (Crawford and Beales, 1983). Occurrences of lead are known also in sandstones of the Upper Devonian and Lower Mississippian Pocono Group in Pennsylvania and West Virginia (Smith, 1977; Clark, 1987; Cannon and others, in press). These occurrences, along with the major base-metal deposits in Appalachian Zn deposits, record the passage of metal-bearing fluids through sedimentary rocks of the Appalachian basin and show that conditions were favorable for precipitation locally in clastic host rocks ranging in age from Cambrian through Mississippian.
On the delineation of permissive tracts
The permissive tract includes the Lower Cambrian and Lower Cambrian(?) basal clastic sequences, the Silurian clastic sequence (Shawangunk Formation, Bloomsburg Formation, Tuscarora Quartzite, and stratigraphically equivalent clastic units) and the Upper Devonian and Lower Mississippian Pocono Group (sandstone) and its stratigraphic equivalents that are predominantly sandstone. The Cambrian basal clastic sequences, including the Cheshire Quartzite in Vermont, the Potsdam Sandstone in New York, and other stratigraphically equivalent units, are considered permissive for the occurrence of sandstone-hosted lead-zinc deposits because of their predominantly clastic composition and position overlying feldspathic basement rocks.
Boundaries for this tract, where exposed at the surface, were derived from contacts on the map showing the generalized geologic setting for metal deposits in the Appalachians (J.D. Peper, written commun.; see Gair and others, 1987) and from State geologic maps. Contacts were projected to 1 km beneath the surface by structural interpretation by John Peper and Howard Pohn and by interpretation of stratigraphic sections and lithofacies maps of the Mississippian System (Dally, 1956; deWitt and others, 1979; Craig and Conner, 1979) by Antoinette Geoly. The western limit of the permissive tract was drawn where sedimentary rocks of the Osage Series of the Mississippian System that are composed of greater than 80 percent detrital components have sandstone:shale ratios of less than 1:1.
On the numerical estimates made
No estimates of undiscovered deposits were made for this tract because, while occurrences of galena are known in the region, large sandstone-hosted lead-zinc deposits are uncommon on a worldwide basis. The lack of any known large deposits in the eastern United States or other indications beyond appropriate geologic settings over broad areas were not considered an adequate basis for estimating undiscovered resources of this deposit type.
Ayuso, R.A., Foley, N.K., and Brown, C.E., 1987, Source of lead and mineralizing brines for Rossie-type Pb-Zn veins in the Frontenac axis area, New York: Economic Geology, v. 82, no. 2, p. 489-496.
Bjørlykke, A., and Sangster, D.F., 1981, An overview of sandstone lead deposits and their relation to red-bed copper and carbonate-hosted lead-zinc deposits, in Skinner, B.J., ed., Economic Geology Seventy-Fifth Anniversary Volume, 1905-1980: Lancaster, Pennsylvania, Economic Geology Publishing Company, p. 179-213.
Cannon, W.F., Clark, S.H.B., Lesure, F.G., Hinkle, M.E., Paylor, R.L., King, H.M., Simard, C.M., Ashton, K.C., and Kite, J.S., 1994, Mineral resources of West Virginia: U.S. Geological Survey Miscellaneous Investigations Series Map I-2364-A, scale 1:500,000, with pamphlet, 14 p.
Clark, S.H.B., 1987, Metallogenic map of zinc, lead, and barium deposits and occurrences in Paleozoic sedimentary rocks, east-central United States: U.S. Geological Survey Miscellaneous Investigations Series Map I-1773, scale 1:2,500,000 with pamphlet, 77 p.
Craig, L.C., and Connor, C.W., coordinators, 1979, Paleotectonic investigations of the Mississippian System in the United States: U.S. Geological Survey Professional Paper 1001, pt. III., plates 4-B and 9-B.
Crawford, M.J., and Beales, F.W., 1983, The Shawangunk mine—A possible sandstone-hosted Mississippi Valley-type ore deposit in New York, in Kisvarsanyi, Geza, Grant, S.K., Pratt, W.P., and Koening, J.W., eds., International conference on Mississippi Valley type lead-zinc deposits: Rolla, University of Missouri, p. 436-445.
deWitt, Wallace, Jr., and McGrew, L.W., 1979, The Appalachian basin region, in Craig, L.C., and Connor, C.W., coordinators, Paleotectonic investigations of the Mississippian System in the United States: U.S. Geological Survey Professional Paper 1001, pt. I, p. 13-48.
Dally, J.L., 1956, The stratigraphy and paleontology of the Pocono Group in West Virginia: New York, Columbia University, unpub. Ph.D. dissertation, 248 p.
Gair, J.F., Cannon, W.F., Peper, J.D., Cannon, S.S., and Martin, B., 1987, Appalachian metallogenic map (abs.), in Sachs, J.S., ed., USGS research on mineral resources—1987, Third Annual V.E. McKelvey Forum on Mineral and Energy Resources: U.S. Geological Survey Circular 995, p. 22–23.
Kyle, J.R., and Gutierrez, G.N., 1988, Origin of the Indian Creek sandstone-hosted lead deposits, southeast Missouri, USA, in Zachrisson, Ebbe, ed., Proceedings of the Seventh Quadrennial IAGOD Symposium, Luleå, Sweden, 1986: Stuttgart, E. Schweizerbart’sche Verlagsbuchhandlung, p. 669–684.
Lindblom, Sten, 1986, Textural and fluid inclusion evidence for ore deposition in the Pb-Zn deposit at Laisvall, Sweden: Economic Geology, v. 81, no. 1, p. 46-64.
Martens, J.H.C., 1964, Minerals of West Virginia: West Virginia Geological and Economic Survey, Educational Series 8, 41 p.
Peper, J.D., in prep., Map showing the generalized geologic setting for metal deposits in the Appalachians: U.S. Geological Survey Miscellaneous Investigations Series Map, 2 sheets, scale 1:1,000,000.
Rickard, D.T., Willdén, M.Y., Marinder, N.-E., and Donnelly, T.H., 1979, Studies on the genesis of the Laisvall sandstone lead-zinc deposit, Sweden: Economic Geology, v. 74, no. 5, p. 1255-1285.
Schrijver, K., and Beaudoin, G., 1987, Diverse occurrences of galena-cemented sandstones in the Paleozoic, northern Appalachians, Quebec: Canadian Institute of Mining and Metallurgy Bulletin, v. 80, no. 908, p. 54–62.
Smith, R.C., II, 1977, Zinc and lead occurrences in Pennsylvania: Pennsylvania Geological Survey, Mineral Resources Report 72, 318 p.