Four Bear

Prospect in Alaska, United States with commodities Silver, Gold, Copper, Lead, Zinc, Arsenic, Mercury

Geologic information

Identification information

Deposit ID 10308093
Record type Site
Current site name Four Bear
Alternate or previous names Pmrgx-28

Geographic coordinates

Geographic coordinates: -161.10244, 55.60623 (WGS84)
Relative position The Four Bear prospect is located on the Alaska Peninsula approximately 5 miles southeast of Mount Dana. The map site is at an elevation of about 2,250 feet, near the center of sec. 8, T. 53 S., R. 77 W., Seward Meridian. It is referred to as PMRGX-28 in Wilson and others (1988, locality 76). The location is accurate to within 1,200 feet.
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Geographic areas

Country State
United States Alaska


Commodity Importance
Silver Primary
Gold Primary
Copper Primary
Lead Primary
Zinc Primary
Arsenic Secondary
Mercury Secondary

Materials information

Materials Type of material
Pyrite Ore
Sphalerite Ore
Calcite Gangue
Opal Gangue
Quartz Gangue
Tourmaline Gangue


  • (Local) Alteration ranges from propylitic to argillic to sericitic, along with local silicification.

Mineral occurrence model information

Model code 53
USGS model code 17
Deposit model name Porphyry Cu
Mark3 model number 4
Model code 78
USGS model code 20c
Deposit model name Porphyry Cu-Au
Mark3 model number 34

Nearby scientific data

(1) -161.10244, 55.60623

Comments on the geologic information

  • Geologic Description = At the Four Bear prospect, siltstone, shale, sandstone, and conglomerate of the Upper Cretaceous Hoodoo Formation are cut by intrusive rocks that include diorite and rhyolite-rhyodacite quartz porphyry (Wilson and others, 1995). The diorite exhibits propylitic, argillic, and sericitic alteration. The younger rhyolite-rhyodacite quartz porphyry forms the central part of the prospect area. It contains as much as 20 percent disseminated pyrite and is pervasively sericitized. Locally, it is silicified and contains small stockworks of thin pyrite veins. Quartz and quartz-calcite veins 0.25 to 2 inches wide occur in widely scattered shears (Freeport Exploration Company, 1985). Pebble and breccia dikes occur in the intrusives and in the surrounding sedimentary rock. Opal and sphalerite occur in the dikes. Tourmaline is present in a breccia pipe. The sedimentary rocks are intensely hornfelsed and iron stained up to 1,000 feet from the intrusive rocks. Resource Associates of Alaska outlined a gold soil anomaly area of approximately 1,000 by 2,000 feet and an arsenic soil anomaly area of 3,000 by 3,500 feet (Trujillo and others, 1983). Their soil samples contained as much as 0.21 ppm gold, and their rock samples contained as much as 0.08 ppm gold, 5.5 ppm silver, 273 ppm copper, 450 ppm lead, 544 ppm zinc, 595 ppm arsenic, and 0.08 ppm mercury. Freeport Exploration Company collected six rock samples that had anomalous gold values. The tourmaline-bearing breccia contained 0.11 ppm gold and 1.4 ppm silver.
  • Age = Tertiary.

Economic information

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Inactive

Mining district

District name Alaska Peninsula

Comments on the workings information

  • Workings / Exploration = In 1983, Resource Associates of Alaska mapped the prospect and collected 87 rock and soil samples. The highest metal values in their rock samples were as much as 0.08 ppm gold, 5.5 ppm silver, 273 ppm copper, 450 ppm lead, 544 ppm zinc, 595 ppm arsenic, and 0.08 ppm mercury. In 1984, Freeport Exploration Company mapped the prospect and took 41 rock and 106 soil samples. Six samples contained anomalous gold values.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF PM015

Bibliographic references

  • Deposit

    Trujillo, R.S., Farnham, S., and Anderson, G.,1983, Exploration and evaluation of precious metal potential of the Aleut Corporation 14(h)8 lands, southwest Alaska: Resource Associates of Alaska report, 25 p., 11 map sheets, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.)

  • Deposit

    Freeport Exploration Company, 1985, 1984 report of activities, Canoe Bay joint venture: Freeport Exploration Company, 25 p. (Report held by the Aleut Corporation, Anchorage, Alaska.)

  • Deposit

    Angeloni, L.M., Wilson, F.H., and Sutlet, S., 1985, Map and tables showing preliminary rock geochemical data, Port Moller, Stepovak Bay, and Simeonof Island quadrangles, Alaska: U.S. Geological Survey Open-File Report 85-470, 179 p., 1 map sheet, scale 1:250,000.

  • Deposit

    Wilson, F.H., White, W.H., and DuBois, G.D., 1988, Brief descriptions of mines, prospects, and mineral occurrences in the Port Moller and Stepovak Bay quadrangles, Alaska Peninsula: U.S. Geological Survey Open-File Report 88-666, 128 p., scale 1:250,000.

  • Deposit

    Wilson, F.H., Detterman, R.L., Miller, J. W., and Case, J.E., 1995, Geologic map of the Port Moller, Stepovak Bay, and Simeonof Island quadrangles, Alaska: U.S. Geological Survey Miscellaneous Investigation Series Map I-2272, 1 map sheet, scale 1:250,000.

Comments on the references

  • Primary Reference = Freeport Exploration Company, 1985

General comments

Subject category Comment text
Deposit Model Name = Porphyry Cu, Porphyry Cu-Au (Cox and Singer, 1986; models 17, 20c)
Deposit Model Number = 17, 20c
Deposit Other Comments = the site is located on land patented by, or interim-conveyed to, the Aleut Corporation.

Reporter information

Type Date Name Affiliation Comment
Reporter 25-JAN-01 S.H. Pilcher U.S. Geological Survey