Groundhog Basin

Site Name

Primary: Groundhog Basin

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Commodity

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

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Location

State: Alaska
District: Petersburg

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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: Replacement Sn

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Deposits associated with formation of pyroxene-epidote-garnet skarn.

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Magnetite
Ore: Tetrahedrite
Ore: Pyrrhotite
Ore: Sphalerite
Ore: Arsenopyrite
Ore: Cassiterite
Ore: Chalcopyrite
Ore: Cubanite
Ore: Fluorite
Ore: Galena
Ore: Tennantite
Gangue: Quartz
Gangue: Pyroxene

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Comments

Comment (Geology): Age = 15-17 Ma based on genetic tie to a dated zinnwaldite 'tin' granite nearby (Newberry and Brew, 1989).

Comment (Geology): Geologic Description = The country rocks in the area of the prospects include Tertiary to Cretaceous biotite schist, biotite-garnet-quartz schist, quartzofeldspathic gneiss, and minor marble and calcsilicate gneiss (Brew, 1997 [OF 97-156-H]). The metamorphic rocks near the prospects are cut by several large Tertiary felsic dikes and sills that have been dated elsewhere at about 20 m.y. (see PE043), and by a large Cretaceous tonalite pluton that intrudes the metamorphic section less than 3,000 feet west of the Groundhog Basin deposits. The deposits are also genetically related to a zinnwaldite 'tin' granite plug nearby (Newberry and Brew, 1989). ? Four distinct steeply-dipping 'ore beds' have been defined, the most extensive of which is 4 feet thick and extends horizontally for about 3,700 feet through a vertical distance of about 1,500 feet (Gault and others, 1953). The ore beds consist of a) masses of ore minerals up to several feet thick, mainly of sphalerite, pyrite, pyrrhotite, galena, chalcopyrite, magnetite, and cubanite(?); and b) layers containing the same assemblage of ore minerals disseminated through the metamorphic host rock. The ore beds are interlayered with steeply-dipping, medium- to high-grade pelitic and quartzofeldspathic schist and gneiss, and locally with banded calcsilicate gneiss. Garnet, pyroxene, and epidote are common near the ore beds, and locally form skarns. ? Newberry and Brew (1989) identified tin as cassiterite as a major constituent of the ore beds and has classified the deposits as Ag-Sn-Pb-Zn skarns that replace calcareous beds in the schist and gneiss. They also genetically tie the skarns to a 15-17 Ma, zinnwaldite 'tin' granite that crops out north of the deposits. Near this zinnwaldite granite, massive sulfide samples commonly contain several percent tin and selected samples contain up to 18%. The sequence of depositional events is: 1) formation of pervasive albite-zinnwaldite gneiss in the cupola of an evolving granite with formation of pyroxene-garnet in adjacent biotite schist and mafic dikes; 2) lower temperature zinnwaldite-sphalerite-cassiterite veins in the granite and formation of the Ag-Sn-Pb-Zn ore bodies in Groundhog Basin by replacement of calcareous layers in the schist and gneiss; and 3) peripheral sphalerite-galena-fluorite veins as distal, lower temperature manifestation of the granite-related hydrothermal system. ? the molybdenite-fluorite deposits that overlap this site are described separately at PE043; they are almost certainly related to the Tertiary felsic dikes and sills here and may well be part of the same series of events that formed the zinnwaldite 'tin' granite described by Newberry and Brew (1989).

Comment (Deposit): Other Comments = Gault and other (1953) provide detailed maps of the underground workings as well as a detailed surface geologic map that covers Groundhog Basin and extends southward to Glacier Basin.

Comment (Commodity): Gangue = various calcsilicate skarn minerals

Comment (Exploration): Status = Active

Comment (Commodity): Ore Material = tetrahedrite-tennanite

Comment (Production): Production Notes = No record of production.

Comment (Reference): Primary Reference = Gault and others, 1953; Newberry and Brew, 1989

Comment (Deposit): Model Name = Banded Ag-Sn-Pb-Zn skarn (Cox and Singer, 1986; model 14c)

Comment (Reserve-Resource): Reserves = Gault and others (1943, p. 23-27), document various attempts to define the ore reserves and resources of the deposit and to quantify the size and grade of certain portions of the 'ore beds.' They conclude, however, that there is insufficient information to justify making detailed estimates of the ore reserves in Groundhog Basin. However, in summary, they state, '...it appears reasonably certain that several hundred thousand tons each of solid and disseminated ore are present.' the solid ore contains about 8 percent of zinc, 1.5 percent of lead, and 1.5 ounces of silver per ton. The disseminated ore contains about 2.5 percent of zinc and 1 percent of lead.? Newberry and Brew (1989) have estimated the deposit contains about 1 million tonnes of ore containing 0.8% tin but emphasize the great uncertainty in the estimate.

Comment (Workings): Workings / Exploration = The deposits were discovered in 1904 and were extensively explored, mainly in 1916-1917 and the early 1940's by surface trenching, about 450 feet of underground workings from four adits, and at least 600 feet of diamond drill holes. Claims are still active on the property in 1998.

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References

Reference (Deposit): Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Petersburg quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-870, 53 p.

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): Gault, H.R., Rossman, D.L., Flint, G.M., Jr., and Ray, R.G., 1953, Some lead-zinc deposits of the Wrangell district, Alaska: U.S. Geological Survey Bulletin 998-B, p. 15-58.

Reference (Deposit): Grybeck, D.J., Berg, H.C., and Karl, S.M., 1984, Map and description of the mineral deposits in the Petersburg and eastern Port Alexander quadrangles: U.S. Geological Survey Open-File Report 84-837, 86 p., 1 sheet, scale 1:250,000.

Reference (Deposit): Buddington, A.F., 1923, Mineral deposits of the Wrangell district; U.S. Geological Survey Bulletin 739, p. 51-75.

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Petersburg quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-415, 1 sheet, scale 1:250,000.

Reference (Deposit): Brew, D. A., Ovenshine, A. T., Karl, S. M., and Hunt, S. J., 1984, Preliminary reconnaissance geologic map of the Petersburg and parts of the Port Alexander and Sumdum 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 84-405, 43 p., 2 sheets, scale 1:250,000.

Reference (Deposit): Newberry, R.J., and Brew, D.A., 1989, Epigenetic hydrothermal origin of the Groundhog Basin-Glacier Basin silver-tin-lead-zinc deposits, southeastern Alaska: U.S. Geological Survey Bulletin 1903, p. 113-121.

Reference (Deposit): Brew, D.A., 1997, Reconnaissance geologic map of the Petersburg C-1 quadrangle, southeastern Alaska: U.S. Geological Survey Open-File Report 97-156-H, 23 p., 1 sheet, scale 1:63,360.

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