Portage Bay mine

Mine, Probably inactive

Alternative names

Portage Gold mines

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Cu; Pb; Zn
Ore minerals chalcopyrite; galena; gold; pyrite; pyrrhotite; sphalerite
Gangue minerals graphite; quartz

Geographic location

Quadrangle map, 1:250,000-scale SR
Quadrangle map, 1:63,360-scale D-5
Latitude 60.8641
Longitude -148.5348
Nearby scientific data Find additional scientific data near this location
Location and accuracy The mine workings are located at an elevation of 1,500 feet at the head of the valley opening into Poe Bay, in the SE1/4 section 15, T. 9 N., R. 5 E., of the Seward Meridian. The location shown on the Seward D-5 1:63,000-scale map is where the mill site and camp were located. This is location 131 of Condon and Cass (1958), location 58 of Cobb and Richter (1972), location 88 of MacKevett and Holloway (1977), location 138 of Cobb and Tysdal (1980), and location S-168 of Jansons and others (1984). Cobb and Tysdal (1980) summarized the relevant references under the name of Portage Bay Mine Co. This location is accurate to within 300 feet.

Geologic setting

Geologic description

The country rocks at the Portage Bay mine (labeled Portage Mine on the map) are slate of the Valdez Group of Late Cretaceous age and Oligocene granite dikes (Cobb and Tysdal, 1980). The deposit consists of sulfide-bearing, banded quartz veins in a shear zone at the contact between the slate and the granite. In addition to gold, the veins contain as much as about 1 percent sulfides, including pyrite, pyrrhotite, chalcopyrite, galena, and sphalerite. Graphite inclusions impart a banding to the veins. Spotty gold values occur both in the quartz and along graphitic bands (Roehm, 1936 [PE 95-5]). The principal vein is exposed for 150 feet, averages about 12 inches wide, strikes N60E, and dips 60NW. It is reported to average 1.5 ounces of gold per ton (Roehm, 1936 [PE 95-5]).
The workings consist of 278 feet of crosscut and 345 feet of drift with 220 feet of stopes and 240 feet of raises. One raise, 160 feet in length, reaches the surface at about 1,700 feet above sea level.
Geologic map unit (-148.536909737907, 60.8635127137451)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Oligocene or younger; the veins cut Oligocene intrusive rock.
Alteration of deposit According to Roehm (1936 [PE 95-5]), the dikes intruding the slate are altered to a greenish color, but he did not identify the type of alteration.

Production and reserves

Workings or exploration
The workings consist of 278 feet of crosscut and 345 feet of drift with 220 feet of stopes and 240 feet of raises. One raise, 160 feet in length, reaches the surface at about 1,700 feet elevation. The equipment used in mining consisted of a type 40 Ingersoll-Rand compressor that delivered 150 cubic feet of air per second and Gardner-Denver drills with detachable bits (Roehm, 1936 [PE 95-5]).
In 1980, the U.S. Bureau of Mines collected 13 chip, channel, and grab samples Their assays ranged from a trace to 0.6 ounce of gold per ton and from a trace to 0.16 ounce of silver per ton (Jansons and others, 1984). According to company records, there are reserves of 10,000 tons of ore with a grade of 0.6 ounce of gold per ton (Hoekzema and Sherman, 1983).
Indication of production Yes; small
Reserve estimates Total resources indicated by company records are 10,000 tons of ore containing 0.6 ounce per ton gold (Steiner, 1965).
Production notes Total recorded production is 490 ounces of gold and 60 ounces of silver (Jansons and others, 1984).

Additional comments

This mine location shown on the Seward D-5 USGS topographic map is the site of the mill and support buildings.



Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p.
Reporters Jeff A. Huber (Anchorage)
Last report date 5/12/2000