Londevan

Site Name

Primary: Londevan
Secondary: Lon-De-Van
Secondary: Telegraph group

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Commodity

Primary: Silver
Primary: Lead
Primary: Zinc
Secondary: Gold
Secondary: Copper

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Location

State: Alaska
District: Ketchikan

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Prospect
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Model Name: Polymetallic veins

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Small amounts of pyrite are disseminated in the country rocks adjacent to the veins.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Pyrite
Ore: Galena
Ore: Chalcopyrite
Gangue: Quartz
Gangue: Calcite
Gangue: Albite

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Comments

Comment (Production): Production Notes = Some ore was mined in the early 1900s and stockpiled at the water's edge, but not shipped (Cobb and Elliott, 1980, p. 68).

Comment (Workings): Workings / Exploration = The deposit was discovered in the early 1900s and originally referred to as the Telegraph group. By 1913, a 4350-foot-long adit had been abandoned, apparently due to oxygen-poor air (Maas and others, 1995, p. 202). Efforts as recent as the 1980s to examine or reopen the mine also have been hampered or abandoned because of bad air. Sampling of the main vein system by Maas and others (1995, p. 209-210) was limited by bad air and caving. A chip sample of a subparallel vein about 650 feet into the adit contained 237.7 ppm Ag, 4300 ppm Pb, and 1.84% Zn across 3.5 feet; and a selected sample of the same vein contained 936 ppm Ag and 6.43% Zn. Two samples across a 12-foot-thick portion of quartz in the main drift averaged 5 ppm Ag and 68 ppb Au, along with minor Pb and Zn.

Comment (Geology): Age = The fissure veins probably are Cretaceous or younger in age.

Comment (Deposit): Model Name = Polymetallic veins (Cox and Singer, 1986; model 22c)

Comment (Geology): Geologic Description = The country rocks in this part of Revillagigedo Island are marine, pelitic phyllite and schist that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by a stock and probably related plugs of Tertiary gabbro (Berg and others, 1988). The strata and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time. These regionally metamorphosed rocks subsequently were locally contact metamorphosed to hornblende hornfels near the contacts of Cretaceous granodiorite plutons that were emplaced after the regional metamorphism, and then more widely remetamorposed to hornblende hornfels near the contacts of the Tertiary gabbro. The premetamorphic age range of the pelitic strata is uncertain. Berg and others (1988) assign them a Mesozoic or (Late) Paleozoic age; Brew and Ford (1998) and Crawford and others (in press) assign them to the Gravina belt, of Late Jurassic or Cretaceous age. ? the Londevan deposit consists of sulfide-bearing quartz-calcite(-albite?)-fissure veins in dark gray, graphitic, pelitic phyllite and argillite. The country rocks locally are intruded by dikes or sills of feldspar-porphyritic granodiorite (Wright and Wright, 1988, p. 150; Cobb and Elliott, 1980, p. 68). The main vein and several subparallel, smaller veins dip steeply and strike NW, parallel to the foliation of the country rocks. Many of these veins are adjacent to the granodiorite intrusions. The main vein is about 3 feet thick; the other veins are up to about a foot thick. These veins generally contain 5% or less of pyrite, sphalerite, and galena, and traces of chalcopyrite, silver, and gold. Slickensides and sulfide minerals are common along the footwall portions of these veins. Small amounts of pyrite also are disseminated in the metapelite country rocks. The veins have been traced on the surface for several hundred feet along strike, and the main vein was followed in underground workings for about 2100 feet. Another set of quartz veins that is older than the main vein system follows an anastomosing shear zone that strikes east and dips steeply south (Maas and others, 1995, p. 203). Brooks (1902, p. 63) describes a set of east-west fissure veins, the largest of which is 12 feet thick. These veins contain pyrite, and, locally, considerable argentiferous galena.? the deposit was discovered in the early 1900s and originally referred to as the Telegraph group. By 1913, a 4350-foot-long adit had been abandoned, apparently due to oxygen-poor air (Maas and others, 1995, p. 202). Efforts as recent as the 1980s to examine or reopen the mine also have been hampered or abandoned because of bad air. Some ore was mined in the early 1900s and stockpiled at the water's edge, but not shipped (Cobb and Elliott, 1980, p. 68). Sampling of the main vein system by Maas and others (1995, p. 209-210) was limited by bad air and caving. A chip sample of a subparallel vein about 650 feet into the adit contained 237.7 ppm Ag, 4300 ppm Pb, and 1.84% Zn across 3.5 feet; and a selected sample of the same vein contained 936 ppm Ag and 6.43% Zn. Two samples across a 12-foot-thick portion of quartz in the main drift averaged 5 ppm Ag and 68 ppb Au, along with minor Pb and Zn.

Comment (Reference): Primary Reference = Wright and Wright, 1908; Maas and others, 1995

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References

Reference (Deposit): Wright, F.E., and Wright, C.W., 1908, The Ketchikan and Wrangell mining districts, Alaska: U.S. Geological Survey Bulletin 347, 210 p.

Reference (Deposit): Brooks, A.H., 1902, Preliminary report on the Ketchikan mining district, Alaska, with an introductory sketch of the geology of southeastern Alaska: U.S. Geological Survey Professional Paper 1, 120 p.

Reference (Deposit): Crawford, M.L., Crawford, W.A., and Gehrels, G.E., 2000, Terrane assembly and structural relationships in the eastern Prince Rupert quadrangle, British Columbia, in H.H. Stowell and W.C.McClelland, eds., Tectonics of the Coast Mountains, southeastern Alaska and British Columbia: Boulder, Colorado, Geological Society of America Special Paper 343, p. 1-21.?

Reference (Deposit): Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p.

Reference (Deposit): Brew, D.A., and Ford, A.B., 1998, The Coast Mountains structural zones in southeastern Alaska--descriptions, relations, and lithotectonic significance, in Gray, J.E., and Riehle, J.R., eds., The U.S. Geological Survey in Alaska--geological studies in Alaska by the U.S. Geological Survey in 1996: U.S. Geological Survey Professional Paper 1595, p. 183-192.

Reference (Deposit): Berg, H.C., Elliott, R.L., and Koch, R.D., 1988, Geologic map of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Mineral Investigations Series Map MF-1807,27 p., scale 1:250,000.

Reference (Deposit): Cobb, E.H., and Elliott, R.L., 1980, Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 80-1053, 154 p.

Reference (Deposit): Elliott, R.L., Berg, H.C., and Karl, Susan, 1978, map and table describing metalliferous and selected nonmetalliferous mineral deposits, Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-file Report, 78-73-B,17 p., scale 1:250,000.

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