Rat Fork-Headwall

Site Name

Primary: Rat Fork-Headwall

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Commodity

Primary: Zinc
Primary: Lead
Primary: Silver
Primary: Copper
Secondary: Arsenic
Secondary: Cadmium

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Location

State: Alaska
District: McGrath

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

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

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Physiography

Not available

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Mineral Deposit Model

Model Name: Skarn Zn-Pb

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Extensive oxidation of pyrite-rich areas to ferricrete gossan.

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Rocks

Role: Host
Age Type: Associated Rock
Age in Years: 30.000000+-5.000000
Dating Method: K-Ar
Age Young: Late Oligocene
Age Old: Middle Eocene

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Analytical Data

Not available

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Materials

Ore: Pyrrhotite
Ore: Chalcopyrite
Ore: Galena
Ore: Pyrite
Ore: Marmatite
Ore: Sphalerite
Gangue: Clinopyroxene
Gangue: Epidote
Gangue: Garnet

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Comments

Comment (Geology): Geologic Description = The Rat Fork-Headwall prospect consists of disseminated to massive sulfide veins in a calc-silicate skarn zone within an extensive, east-west-trending, granodiorite dike swarm more than 1.5 kilometers wide (Bundtzen Kline, and Clough, 1982). The dike swarm cuts Lower Paleozoic clastics and carbonates of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The dikes are not dated at the prospect site, but are similar to dikes that are spatially related to the Tin Creek-Midway prospect (MG043) to the northeast, which has yielded K-Ar ages ranging in age from 25 to 35 Ma (Solie and others, 1991; Bundtzen, Harris, and Gilbert, 1997). ? the calc-silicate skarns, which are composed of garnet, epidote, and low temperature clinopyroxene (johannsenite) occur mainly in arenaceous, recrystallized limestone. The sulfide bearing vein parallels a pervasive joint set which cuts various calc-silicate rocks and limestone (Smith and Albanese, 1985). The sulfide vein trends N85W, dips 85S, varies from 0.5 to 3 meters thick, and can be traced for about 22 meters along strike. Principle sulfide minerals in the vein consist of pyrite, sphalerite (iron-rich marmatite), galena, and chalcopyrite. Sulfides locally compose up to 45 percent of the vein, even in thickened areas. Chip-channel samples taken across the vein at three intervals contained up to 0.56 percent copper, 11.10 percent lead, 14.10 percent zinc, 301 grams/tonne silver, 3.80 percent arsenic, 0.12 percent cadmium, and 42.40 percent iron (Smith and Albanese, 1985).

Comment (Workings): Workings / Exploration = In the late 1960s and early 1970s (records are unclear), Falconbridge Minerals through exploration operator St. Eugene Mining Company, conducted a limited amount of diamond core drilling from two stations near the sulfide vein. Based on drill hole orientations, the exploration drilling attempted to intersect the vein at depth. The results of this exploration work are unknown.? Surface sampling has been conducted by Reed and Elliott (1968, C 596), Bundtzen, Kline, and Clough (1982) and Smith and Albanese (1985).

Comment (Geology): Age = Unknown; inferred to be 25 to 35 Ma, based on K-Ar dating of similar granodiorite dike swarms elsewhere in McGrath quadrangle.

Comment (Geology): Age = Chron age is for a similar granodiorite dike swarms elsewhere in McGrath quadrangle.

Comment (Exploration): Status = Inactive

Comment (Deposit): Other Comments = the Rat Fork-Headwall prospect is part of a widespread polymetallic mineral belt similar to other deposits in the Farewell Mineral belt, including Tin Creek North (MG041), Tin Creek South (MG044), Bowser Creek-Main (MG068), Bowser Creek Northeast (MG067), and Smith Lake (MG055) prospects.

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

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

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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): 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): Cobb, E.H., 1972, Metallic mineral resources map of the McGrath quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-379, 1 sheet, 1:250,000 scale.

Reference (Deposit): Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Iliamna, Lake Clark, Lime Hills, and McGrath quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-485, 101 p.

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): 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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