Lucky Four

The Lucky Four is a copper 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: Lucky Four
Secondary: Hump Island

Commodity

Primary: Copper
Secondary: Gold

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: Porphyry Cu

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: Locally intense silicification, argillization, and sericitization. Local iron-staining and oxidation of copper minerals.

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Chalcopyrite
Ore: Molybdenite
Ore: Pyrite
Gangue: Quartz

Comments

Comment (Workings): Workings / Exploration = Assays of samples of sulfide-bearing veins and altered country rocks collected in the early 1990s by the U.S. Bureau of Mines ranged from 806-3080 ppm Cu (average: 2064 ppm Cu) and 6-236 ppm Mo (average: 69 ppm Mo), along with as much as 3.6 ppm Ag, 3837 ppb Au, 172 ppm Bi, and 11 ppm Te (Maas and others, 1995, p. 278 and fig. 73). Other samples of sulfide-bearing altered rocks contained up to 2.0% Cu, 10 ppm Ag, 30 ppm Mo, and 500 ppm Co (Elliott and others, 1978, loc. 41).

Comment (Geology): Age = Probably Late Cretaceous.

Comment (Deposit): Model Name = Metamorphosed porphyry Cu deposit (Cox and Singer, 1986; model 17)

Comment (Geology): Geologic Description = The country rocks on and near Hump Island consist chiefly of flyschlike metasedimentary rocks and subordinate andesitic and basaltic metavolcanic rocks that are intruded by Cretaceous feldspar-porphyritic granodiorite stocks, sills, and dikes (Berg and others, 1988). The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time (Brew, 1996, p. 27). Near some of the granodiorite contacts, the phyllite and semischist were subsequently contact metamorphosed to hornblende hornfels (Berg and others, 1988). The premetamorphic age range of the strata is unknown; Berg and others (1988, p. 17) note that they closely resemble Upper Jurassic and mid-Cretaceous marine flysch and volcanic rocks nearby on Gravina Island.? Hump Island consists largely of intensely hydrothermally altered and locally sulfide-bearing rocks. Maas and others (1995, p. 277) describe the island as a small, foliated, Cretaceous quartz diorite or quartz monzonite pluton that intrudes Jurassic or Cretaceous mafic to felsic volcanic rocks and interbedded pelitic sedimentary rocks. Weak porphyry copper mineralization accompanied emplacement of the pluton, along with silicic and argillic alteration of the surrounding country rocks. The east side of the island is underlain by felsic volcanic rocks that have been altered to quartz-sericite-pyrite schist with a high silica content. The west side is intensely argillized pelitic schist. ? the deposit consists of pyrite, chalcopyrite, and minor molybdenite that form veinlets and disseminations in the hydrothermally altered rocks. Locally, chalcopyrite, and possibly other sulfides, occur as small masses in quartz veinlets (Maas and others, 1995, p. 278). Assays of samples of sulfide-bearing veins and altered country rocks collected in the early 1990s by the U.S. Bureau of Mines ranged from 806-3080 ppm Cu (average: 2064 ppm Cu) and 6-236 ppm Mo (average: 69 ppm Mo), along with as much as 3.6 ppm Ag, 3837 ppb Au, 172 ppm Bi, and 11 ppm Te (Maas and others, 1995, p. 278 and fig. 73). Other samples of sulfide-bearing altered rocks contained up to 2.0% Cu, 10 ppm Ag, 30 ppm Mo, and 500 ppm Co (Elliott and others, 1978, loc. 41). Maas and others (1995, p. 278) classify the prospect as a metamorphosed porphyry Cu deposit, and note that it is the only one known in the Ketchikan district.

Comment (Reference): Primary Reference = Maas and others, 1995

References

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): 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.

Reference (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.

Reference (Deposit): Brew, D.A., 1996, Geologic map of the Craig, Dixon Entrance, and parts of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2319, 53 p., 1 sheet, scale 1:250,000.

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