Groundhog Basin

Prospect in Alaska, United States with commodities Silver, Lead, Tin, Zinc, Gold, Copper, Molybdenum, Tin

Geologic information

Identification information

Deposit ID 10000272
MRDS ID A010316
Record type Site
Current site name Groundhog Basin
Related records 10283078

Geographic coordinates

Geographic coordinates: -132.06378, 56.51475 (WGS84)
Relative position Coordinates are for the approximate center of a group of prospects, adits, and occurrences in an area about 1/4 mile long in upper Groundhog Basin. The site is in the NW1/4, section 7, T. 62 S., R. 86 E. between an elevation of 2,000 and 2,500 feet. Gault and other (1953) includes an excellent detailed geologic map of the site.
(click for info)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Silver Primary
Lead Primary
Tin Primary
Zinc Primary
Gold Secondary
Copper Secondary
Molybdenum Secondary
Tin Secondary

Comments on the commodity information

  • Gangue = various calcsilicate skarn minerals
  • Ore Material = tetrahedrite-tennanite

Materials information

Materials Type of material
Arsenopyrite Ore
Cassiterite Ore
Chalcopyrite Ore
Cubanite Ore
Fluorite Ore
Galena Ore
Magnetite Ore
Pyrrhotite Ore
Sphalerite Ore
Tennantite Ore
Tetrahedrite Ore
Pyroxene Gangue
Quartz Gangue

Alteration

  • (Local) Deposits associated with formation of pyroxene-epidote-garnet skarn.

Mineral occurrence model information

Model code 44
USGS model code 14c
Deposit model name Replacement Sn

Host and associated rocks

  • Host or associated Associated
    Rock type Plutonic Rock > Mafic Intrusive Rock > Diorite
    Rock unit name Coast Range Batholith
    Rock description Coast Range Batholith
  • Host or associated Host
    Rock type Metamorphic Rock > Gneiss

Nearby scientific data

(1) -132.06378, 56.51475

Comments on the geologic information

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

Economic information

Economic information about the deposit and operations

Development status Prospect
Commodity type Both metallic and non-metallic

Comments on exploration

  • Status = Active

Mining district

District name Petersburg

Comments on the production information

  • Production Notes = No record of production.

Reserves and resources

  • Type In-situ
    Estimate year 1943
    Remarks Entry carried over from Old MRDS or added later (i.e. it did not originate in ARDF)
    Commodity Subtype Grade units Group Importance Year
    Zinc Zn 7.37 wt-pct Zinc Major 1943
    Lead Pb 2.21 wt-pct Lead Minor 1943
    Silver Ag 0.049 g/mt Silver Minor 1943

Comments on the reserve resource information

  • 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.

Comments on the workings information

  • 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.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS A010316
USGS Alaska Resource Data File ARDF PE040

Bibliographic references

  • Deposit

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

  • Deposit

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

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

Comments on the references

  • Primary Reference = Gault and others, 1953; Newberry and Brew, 1989

General comments

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

Reporter information

Type Date Name Affiliation Comment
Reporter 01-NOV-98 H.C. Berg U.S. Geological Survey
Reporter 01-NOV-98 D.J. Grybeck U.S. Geological Survey