Unnamed (western Gravina Island)

The Unnamed (western Gravina Island) is a copper and silver mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Unnamed (western Gravina Island)

Commodity

Primary: Copper
Primary: Silver
Secondary: Molybdenum

Location

State: Alaska
District: Ketchikan

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

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

Physiography

Not available

Mineral Deposit Model

Model Name: Polymetallic veins

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: Limestone locally is dolomitized, and rhyolite locally contains conspicuous hydrothermal hematite. Local iron- and copper-staining.

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Pyrite
Ore: Chalcopyrite
Ore: Hematite
Ore: Molybdenite
Gangue: Dolomite
Gangue: Quartz

Comments

Comment (Workings): Workings / Exploration = In 1970, workings consisted of a water-filled adit that probably was driven in the early 1900s. An analysis of a sample of the mineralized breccia showed 1.5 ppm Ag and 2% Cu (Koch and Elliott, 1978 [OFR 78-156A]). Prospecting in this area in the 1960s and 70s reportedly revealed disseminated chalcopyrite and pyrite, and traces of molybdenite and secondary copper minerals in complexly sheared, hydrothermally altered metamorphic and intrusive country rocks (Berg, 1973, p. 37).

Comment (Geology): Age = Late Cretaceous or younger.

Comment (Geology): Geologic Description = The country rocks at this prospect consist of Upper Triassic rhyolite and rhyolite tuff (Berg, 1973, Berg and others, 1988). This formation is depositionally overlain by, and locally in fault contact with, Upper Triassic carbonate, clastic, and basaltic volcanic rocks. The strata were regionally metamorphosed to prehenite-pumpellyite or to low-greenschist grade in Late Cretaceous time. Locally, the limestone is dolomitized, and the rhyolite contains conspicuous hydrothermal hematite. ? the deposit is in iron-stained metarhyolite(?) and consists of a ten-foot-wide breccia zone containing quartz, hematite, dolomite, chalcopyrite, and pyrite (Berg, 1973, p. 37). An analysis of a sample of the mineralized breccia showed 1.5 ppm Ag and 2% Cu (Koch and Elliott, 1978; OFR 78-156A). In 1970, workings consisted of a water-filled adit that probably was driven in the early 1900s. Prospecting in this area in the 1960s and 70s reportedly revealed disseminated chalcopyrite and pyrite, and traces of molybdenite and secondary copper minerals in complexly sheared, hydrothermally altered metamorphic and intrusive country rocks (Berg, 1973, p. 37). Assuming that the mineralized breccia postdates the regional metamorphism, the deposit is Late Cretaceous or younger.

Comment (Reference): Primary Reference = Berg, 1973

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

References

Reference (Deposit): Berg, H.C., 1973, Geology of Gravina Island Alaska: U.S. Geological Survey Bulletin 1373, 41 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.

Reference (Deposit): Koch, R.D., and Elliott, R.L., 1978, Analyses of rock samples from Ketchikan quadrangle, southeastern Alaska: U.S. Geological Survey Open-File Report 78-156-A, 162 p., 1 sheet, scale l:250,000.

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.

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