Four Bear

Prospect, Inactive

Alternative names

PMRGX-28

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Zn
Other commodities As; Hg
Ore minerals pyrite; sphalerite
Gangue minerals calcite; opal; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale PM
Quadrangle map, 1:63,360-scale C-4
Latitude 55.607
Longitude -161.1
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

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.
Geologic map unit (-161.102013554018, 55.6061702069904)
Mineral deposit model Porphyry Cu, Porphyry Cu-Au (Cox and Singer, 1986; models 17, 20c)
Mineral deposit model number 17, 20c
Age of mineralization Tertiary.
Alteration of deposit Alteration ranges from propylitic to argillic to sericitic, along with local silicification.

Production and reserves

Workings or 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.
Indication of production None

Additional comments

The site is located on land patented by, or interim-conveyed to, the Aleut Corporation.

References

MRDS Number 10308093

References

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.)
Trujillo, R.S., Tapper, C.J., Alvarez, T.J., Porterfield, Ben, and Toupe, W.M., 1982, Exploration and evaluation of precious metal potential of portions of Aleut Corporation lands, southwest Alaska 1982: Resource Associates of Alaska unpublished report, 91 p, 33 maps, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Reporters S.H. Pilcher
Last report date 1/25/2001