Map showing lithostratigraphic and structural setting of stratabound (massive) sulfide deposits in the U.S. Appalachians

Strata-bound sulfide deposits at Ducktown, Tennessee, have many characteristics of volcanogenie exhalative deposits but occur in an overwhelmingly sedimentary environment. Lead isotope ratios of galenas and massive pyritic and pyrrhotitic ores fall into three distinct groups that are not related to wall-rock type, type of ore, or to orebody. A positive correlation between the lead and sulfur isotope ratios of galena indicates a relation between sulfur and lead that does not seem to be an effect of metamorphism but is rather an original feature of the ore. The groupings of lead isotope ratios and a possible bimodality of sulfur isotope compositions, as well as the above-mentioned positive correlation, suggest that Ducktown lead and sulfur represent the mixing of two sources. The dominant source of lead was probably U/Pb-enriched clastic sediments. Seawater sulfate may have dominated sulfur contributions from this source. The second source could have been a deep-seated, mafic igneous source tapped by a deep fault associated with late Precambrian rift basin development. The deep source could have provided heat to drive the hydrothermal cell in the sediments, a relatively nonradiogenic component of lead, sulfur with/i34Sz -• 0 per mil, a considerable amount of Cu and Zn, as well as the small amphibolite pods at Ducktown and along strike. Lead isotope studies of contemporaneous rift volcanics, the Mount Rogers Formation, indicate that lead in Ducktown ores could not have been derived from a similar source. Mount Rogers felsic volcanics contain lead derived from a relatively U/Pb-poor, Th/Pbenriched source that appears to have been (granulitized?) Grenville-age basement.Lead-isotope ratios of galenas from the Gossan Lead are similar to those at Ducktown. Other Blue Ridge massive sulfide deposits have less radiogenic 2ø6Pb/2ø4Pb values, but none contain any discernable basement component similar to that of Mount Rogers. Reconnaissance sulfur isotope ratios from other Blue Ridge massive sulfides suggest a tendency toward heavier values than those at Ducktown.

Section: The Dashed Lines Inmentioning

confidence: 98%

Lead and sulfur isotopes and a model for the origin of the Ducktown Deposit, Tennessee

LeHuray¹

1984

“…2). Rocks farther to the southwest, bet.ween the Hayesville thrust and the Brevard zone (formerly designated as the Ashland-Wedowee belt and now in part, the Sandy Springs and New Georgia Groups-- Abrams and McConnell, 1984), may be equivalent to the Ashe Formation and contain a number of small massive sulfide deposits (Hurst and Crawford, 1970;Gair and Slack, 1979). These rocks also are southeast of the Grenvillian core of the Blue Ridge uplift across much of North Carolina, but in the southwestern part of the state the uplifted basement rocks pinch out, possibly passing beneath the Hayesville thrust (Fig.…”

mentioning

confidence: 98%

Deformation, geochemistry, and origin of massive sulfide deposits, Gossan Lead District, Virginia

Gair¹,

Slack²

1984

Self Cite

The Gossan Lead district is a 28-km-long, northeast-trending belt of discontinuous massive sulfide deposits in the Blue Ridge province of southwestern Virginia. The deposits, hosted by the Ashe Formation of late Proterozoic age, consist of strata-bound lenses and layers of massive pyrrhotite, minor chalcopyrite, sphalerite, and pyrite, and rare arsenopyrite and galena. Deposits were mined principally in the Iron Ridge and Betty Baker segments, respectively, at the southwestern and northeastern ends of the belt. Detailed mapping of the Gossan Howard, Huey, and Bumbarger pits in the Iron Ridge segment indicates that the deposits occur at one horizon and have been variously folded and brecciated after sulfide deposition. The Gossan Howard consists of a single, gently dipping lens of sulfide. The Huey deposit is complexly folded and locally contains tectonically thickened ore. The Bumbarger deposit is a lens as much as 40 m thick--the thickest known in the district. This deposit contains abundant coarse breccia fragments of wall rock around which the massive sulfide has flowed (during deformation and metamorphism), probably thickening the original deposit significantly. In the northeastern part of the district, drill holes intersect several sulfide layers that possibly are structurally repeated. The Ashe Formation in the district is a sequence of metasedimentary rocks and local conformable lenses of amphibolite and actinolite-chlorite schist. The metasedimentary rocks include metapelite, quartz-feldspar granofels (metagraywacke), and minor quartziteand carbonaceous schist, and are interpreted as marine turbidites. The amphibolites and other mafic rocks have chemical compositions similar to low Ti tholeiitic basalt, with a high Y/Nb (>10) and high average contents of Co (40 ppm), Cr (403 ppm), Ni (211 ppm), and V (247 ppm). Immobile trace element signatures (Ti-Y-Zr; Th-Hf-Ta; Ti-Cr) suggest a magmatic affinity with midocean ridge basalt (MORB); rare earth elements (REE) have low abundance levels (10)<-15)< chondrite), broadly fiat patterns [(La/Yb)N --0.7-1.1], and a slight depletion in the light elements similar to midocean ridge basalts. An amphibolite from a much higher stratigraphic level, south of the district, differs significantly from the mafic rocks closer to the sulfide zone in having the chemical signature of a transitional, slightly alkalic tholeiite with high TiO• (3.87 wt %), Fe•O3 (16.4 wt %), and P•O5 (0.56 wt %), low Y/Nb (3.3), and a highly fractionated rare earth element distribution [(La/Yb)N = 3.9] similar to continental basalt. Some silicate wall rocks of the deposits are mineralogically and chemically unusual, and differ substantially from the clastic metasediments of the Ashe Formation. Such rocks are composed mainly or wholly of plagioclase feldspar, biotite, chlorite, muscovite, or spessartinerich garnet. The unusual lithologies form local strata-bound lenses in the footwall and/or hanging wall of the deposits, typically within 10 m of massive sulfide. The plagioclase rocks (3.4-7.6 wt % Na•...

“…Other deposits and occurrences: Besides the above described deposits, numerous other smaller massive sulfide deposits are associated with the mafic and felsic volcanic rocks within the Talladega, Ashland, and Wedowee lithotectonic terranes (Table 2) (Shearer and Hull, 1918;Adams, 1930;Kinkel, 1967;Hurst and Crawford, 1970;Tull et al, 1978; and Gair and Slack, 1979). Many of these deposits contain massive pyrite or pyrrhotite with minor base and precious metal values; some of the metal values, though, are associated with disseminated pyrite.…”

Section: Besshi-type Depositmentioning

confidence: 96%

Volcanogenic sulfide deposits in the southernmost Appalachians

Neathery

Hollister²

1984

Volcanogenic massive sulfide deposits in the southernmost Appalachians of east-central Alabama and west-central Georgia are associated with metamorphosed submarine basalts and felsic rocks of the Ashland, Wedowee, and Talladega lithotectonic terranes. These three terranes lie between the Brevard fault on the south and the Talladega-Cartersville and Hayesville faults on the north. The oldest sulfide deposits occur in a regional setting characterized by a thick sequence of metamorphosed Eocambrian to lower Paleozoic continentally derived clastic and intercalated submarine metavolcanic rock. The metamorphosed elastic rocks represent the basal section of a rifted margin prism, whereas the metavolcanic rocks represent rhyolites, andesites, and basalts which were probably erupted along rift zones of a spreading back-arc basin. Most of the volcanogenie massive sulfide deposits are localized within metavolcanic rocks and are rare or absent in the enclosing or interbedded metasedimentary rock. The youngest sulfide deposits occur in the distal part of a volcanic arc sequence of the Talladega terrane, which terminated sediment deposition and volcanic activity in the region. Talladega terrane sulfide deposits appear anomalously young (Devonian) respective to other deposits in the eastern United States.Three types of massive sulfide host rock associations have been recognized in the southernmost Appalachians; Kuroko-type deposits associated with predominantly felsic volcanic assemblages, Anyox-type deposits associated with predominantly mafic volcanic assemblages, and Besshi-type deposits associated with interbedded assemblages of elastic sedimentary and marie volcanic rocks.