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Rat Fork-Headwall

Prospect in Alaska, United States with commodities Silver, Copper, Lead, Zinc, Arsenic, Cadmium
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Commodities
  6. Materials information
  7. Alteration
  8. Mineral occurrence model information
  9. Host and associated rocks
  10. Nearby scientific data
  11. Economic information about the deposit and operations
  12. Mining district
  13. Links to other databases
  14. Bibliographic references
  15. General comments
  16. Reporter information

Geologic information

Identification information

Deposit ID 10002591
MRDS ID A015028
Record type Site
Current site name Rat Fork-Headwall
Related records 10258685

Geographic coordinates

Geographic coordinates: -153.89173, 62.31837 (WGS84)
Relative position The Rat Fork-Headwall prospect is located just below the crest of a steep ridgeline near the head of a glacial cirque, the headward reaches of the Rat Fork of Sheep Creek; it is at about 5,500 feet (1,676 m) elevation, in the NW1/4 sec. 27, T. 26 N., R. 25 W., of the Seward Meridian. The prospect is accurately located; the reporter visited the site in 1982.

Site location context

Political divisions (FIPS codes)

Yukon-Koyukuk(Census area)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

McGrath B-2(quadrangle 1:63,360 scale)

McGrath SE(quadrangle 1:100,000 scale)

McGrath(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Upper Kuskokwim River(hydrologic accounting unit)

Southwest(hydrologic subregion)

Alaska(hydrologic region)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Silver Primary
Copper Primary
Lead Primary
Zinc Critical Primary
Arsenic Critical Secondary
Cadmium Secondary

Materials information

Materials Type of material
Chalcopyrite Ore
Galena Ore
Pyrite Ore
Pyrrhotite Ore
Marmatite Ore
Sphalerite Ore
Clinopyroxene Gangue
Epidote Gangue
Garnet Gangue

Alteration

  • (Local) Extensive oxidation of pyrite-rich areas to ferricrete gossan.

Mineral occurrence model information

Model code 60
USGS model code 18c
Deposit model name Skarn Zn-Pb
Mark3 model number 22

Host and associated rocks

  • Host or associated Host
    Rock type
    Stratigraphic age (youngest) Late Oligocene
    Stratigraphic age (oldest) Middle Eocene
    Chronological age 30
    Dating method K-Ar

Nearby scientific data

(1) -153.89173, 62.31837
ListMap

Economic information

Comments on the geologic information

  • 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).
  • Age = Unknown; inferred to be 25 to 35 Ma, based on K-Ar dating of similar granodiorite dike swarms elsewhere in McGrath quadrangle.
  • Age = Chron age is for a similar granodiorite dike swarms elsewhere in McGrath quadrangle.

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Comments on exploration

  • Status = Inactive

Mining district

District name McGrath

Comments on the workings information

  • 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).

Reference information

Bibliographic references

Comments on the references

  • Primary Reference = Smith and Albanese, 1985

General comments

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

Reporter information

Type Date Name Affiliation Comment
Reporter 30-OCT-1998 T.K. Bundtzen Pacific Rim Geological Consulting

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

Maps centered on this site

Authoritative Alaska resources

These are landing pages for further research — the state agencies don't currently expose per-mine deep links.