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Unnamed (southwest Bostwick Inlet)

Occurrence in Alaska, United States with commodities Zinc, Silver
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Geologic information

Identification information

Deposit ID 10307667
Record type Site
Current site name Unnamed (southwest Bostwick Inlet)

Geographic coordinates

Geographic coordinates: -131.71777, 55.19874 (WGS84)
Relative position This unnamed occurrence is on the southwest shore of Bostwick Inlet, near its mouth, about 0.9 mile north of the south-projecting point at the north entrance of Seal Cove. The site is in section 16, T. 77 S., R. 91 E., of the Copper River Meridian. It corresponds to loc. 309 in Maas and others (1995). The location is accurate within 0.1 mile.
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Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Zinc Primary
Silver Secondary

Materials information

Materials Type of material
Pyrite Ore
Sphalerite Ore

Mineral occurrence model information

Model code 184
USGS model code 28a
Deposit model name Massive sulfide, kuroko
Mark3 model number 93

Nearby scientific data

(1) -131.71777, 55.19874
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Comments on the geologic information

  • Geologic Description = Southern Gravina Island is underlain by an assemblage of undivided Silurian or Ordovician metamorphosed bedded and intrusive rocks; a stock and associated dikes of Silurian trondhjemite that cuts the metamorphic assemblage; and a sequence of Upper Triassic carbonate, clastic, rhyolitic, and basaltic strata that unconformably overlies the older rocks (Berg, 1973, 1982; Berg and others, 1988). The rocks are complexly folded and are cut by high-angle faults and by low-angle thrust faults. In many places, the Triassic rhyolite and the rocks beneath it are permeated by microscopic particles of hydrothermal hematite, giving them a pink, purple, or red hue (Berg, 1973, p. 14). This occurrence consists of stratiform layers, up to 1.6 feet thick, of massive pyrite and sphalerite in Upper Triassic rhyolite at its depositional contact with overlying Upper Triassic carbonaceous slate (H.C. Berg, unpublished field data, 1968; Maas and others, 1995, p. 227). The contact strikes west and dips steeply to the north, and is truncated by a NW-striking, high-angle fault along the southwest shore of Bostwick Inlet (Berg, 1973). Samples collected by Maas and others (1995, p. 229) across about 10 feet of mineralized rock contained up to 1.6% Zn and small amounts of Ag. The characteristics and setting of this occurrence indicate that it is a stratiform, volcanogenic massive-sulfide deposit of Late Triassic age. As such, it is the southernmost known occurrence of a belt of Upper Triassic, stratabound, volcanogenic massive-sulfide deposits in southeastern Alaska (Berg, 1981).
  • Age = Late Triassic.

Economic information

Economic information about the deposit and operations

Development status Occurrence

Comments on exploration

  • Status = Inactive

Mining district

District name Ketchikan

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF KC126

Bibliographic references

  • Deposit

    Berg, H.C., 1973, Geology of Gravina Island Alaska: U.S. Geological Survey Bulletin 1373, 41 p.

  • Deposit

    Berg, H.C., 1982, The Alaska Mineral Resource Assessment Program; guide to information about the geology and mineral resources of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Circular 855, 24 p.

  • 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.

  • 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.

Comments on the references

  • Primary Reference = Maas and others, 1995

General comments

Subject category Comment text
Deposit Model Name = Kuroko massive sulfide (Cox and Singer, 1986; model 28a)

Reporter information

Type Date Name Affiliation Comment
Reporter 05-JUL-99 H.C. Berg U.S. Geological Survey