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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Unnamed (western Gravina Island) MRDS details
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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