Rat Fork-Base

The Rat Fork-Base is a lead, zinc, 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: Rat Fork-Base

Commodity

Primary: Lead
Primary: Zinc
Primary: Copper
Primary: Silver
Secondary: Cadmium
Secondary: Cobalt
Secondary: Iron

Location

State: Alaska
District: McGrath

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: Skarn Zn-Pb

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: Surface oxidation of massive pyrite and pyrrhotite formed a pronounced ferricrete gossan.

Rocks

Role: Associated
Age Type: Associated Rock
Age in Years: 30.000000+-5.000000
Age Young: Oligocene
Age Old: Eocene

Analytical Data

Not available

Materials

Ore: Sphalerite
Ore: Pyrrhotite
Ore: Pyrite
Ore: Chalcopyrite
Gangue: Johannsenite
Gangue: Garnet
Gangue: Epidote
Gangue: Clinopyroxene

Comments

Comment (Reference): Primary Reference = Smith and Albanese, 1985

Comment (Exploration): Status = Inactive

Comment (Geology): Age = Chronological age is for a similar dike swarm in Tin Creek area.

Comment (Geology): Geologic Description = The Rat Fork-Base prospect consists of disseminated sulfides in a calc-silicate hornfels and marble adjacent to an extensive, east-west-trending, granodiorite sill and dike swarm, the same plutonic complex that is exposed at the Rat Fork-Headwall (MG059) prospect. At the Rat Fork-Base prospect, the calc-silicate zone, which consists of garnet, epidote, and clinopyroxene in arkosic, metaclastic rocks, has been intruded by several mafic sills that are parallel to bedding. The plutonic rocks intrude the Lower Paleozoic Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The zone of disseminated mineralization trends roughly east-west, varies from 1 to 10 meters thick , and can be traced along the strike for about 40 meters. Principle sulfide minerals include abundant pyrite and pyrrhotite, and minor amounts of chalcopyrite and sphalerite. . Surface sampling of massive sulfide talus below a diamond drill station contained 0.31 percent copper, 1.85 percent zinc, 6.5 grams/tonne silver, 158 ppm cobalt, 161 ppm cadmium, and 41.4 percent iron (Smith and Albanese, 1985).

Comment (Deposit): Model Name = Lead-zinc (copper) skarn (Cox and Singer, 1986; model 18c).

Comment (Deposit): Other Comments = Similar to Rat Fork-Headwall (MG059), Tin Creek North (MG041), Tin Creek Midway (MG043), Smith Lake (MG055), and Bowser Creek Main (MG068) skarn deposits in the Farewell Mineral belt, McGrath Quadrangle.

Comment (Workings): Workings / Exploration = A single drill station was sited by Falconbridge Minerals through their operator St. Eugene Mining Company sometime in the late 1960s and early 1970s (records for time of activities are poorly known). The results of these exploration efforts are unknown. Surface sampling of massive sulfide talus below the diamond drill station contained 0.31 percent copper, 1.85 percent zinc, 6.5 grams/tonne silver, 158 ppm cobalt, 161 ppm cadmium, and 41.4 percent iron (Smith and Albanese, 1985).

Comment (Geology): Age = Unknown; inferred to be 25 to 35 Ma, based on age of similar dike swarm in Tin Creek area (Solie and others, 1991).

References

Reference (Deposit): Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 pages, one sheet, scale 1:125,000.

Reference (Deposit): Reed, B.L. and Elliott, R.L., 1968, Geochemical anomalies and metalliferous deposits between Windy Fork and Post River, southern Alaska: U.S. Geological Survey Circular 596, 22 pages.

Reference (Deposit): Reed, B.L. and Elliott, R.L., 1968, Geochemical anomalies and metalliferous deposits between Windy Fork and Post River, southern Alaska: U.S. Geological Survey Circular 596, 22 pages.

Reference (Deposit): Solie, D.N., Bundtzen, T.K., and Gilbert, W.G., 1991, K-Ar ages of igneous rocks in the McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File Report 160, 17 pages, one sheet, 1:250,000 scale.

Reference (Deposit): Smith, T.E., and Albanese, M.D., 1985, Preliminary prospect examinations in the McGrath B-2, A-3, and A-4 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 85-54, 19 pages.

Reference (Deposit): Bundtzen, T.K., Kline, J.T., and Clough, J.G., 1982, Preliminary geologic map of the McGrath B-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File report 149, 22 pages, one sheet, scale 1:63,360.

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