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Rat Fork-Base

Prospect in Alaska, United States with commodities Silver, Copper, Lead, Zinc, Cadmium, Cobalt, Iron
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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 10307862
Record type Site
Current site name Rat Fork-Base

Geographic coordinates

Geographic coordinates: -153.87284, 62.31848 (WGS84)
Relative position The Rat Fork-Base prospect is located near the base of the cirque that defines the head of the Rat Fork of Sheep Creek; it is at an elevation of 4,175 feet (1,273 m) in the NW1/4 sec. 26, T. 26 N., R. 25 W., of the Seward Meridian. An active rock glacier forms the southern boundary of the prospect area. The location is accurate; 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
Cadmium Secondary
Cobalt Critical Secondary
Iron Secondary

Materials information

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

Alteration

  • (Local) Surface oxidation of massive pyrite and pyrrhotite formed a pronounced 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 Associated
    Rock type
    Stratigraphic age (youngest) Oligocene
    Stratigraphic age (oldest) Eocene
    Chronological age 30

Nearby scientific data

(1) DSbr
ListMap

Economic information

Comments on the geologic information

  • 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).
  • Age = Unknown; inferred to be 25 to 35 Ma, based on age of similar dike swarm in Tin Creek area (Solie and others, 1991).
  • Age = Chronological age is for a similar dike swarm in Tin Creek area.

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Inactive

Mining district

District name McGrath

Comments on the workings information

  • 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).

Reference information

Comments on the references

  • Primary Reference = Smith and Albanese, 1985

General comments

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

Reporter information

Type Date Name Affiliation Comment
Reporter 06-NOV-98 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.