Tomboy Ledge

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Cu; Pb
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrite
Gangue minerals carbonate; quartz

Geographic location

Quadrangle map, 1:250,000-scale SR
Quadrangle map, 1:63,360-scale D-4
Latitude 60.8736
Longitude -148.3606
Nearby scientific data Find additional scientific data near this location
Location and accuracy The mine is near the top of the divide that separates Pigot Bay and Pirate Cove. The adits are on the Pigot Bay side of the ridge, in the NE1/4 section 15, T. 9 N., R. 6 E., of the Seward Meridian. This is location 127 of Condon and Cass (1958), location 62 of Cobb and Richter (1972), location 85 of MacKevett and Holloway (1977), location 134 of Cobb and Tysdal (1980), and location S-162 of Jansons and others (1984). This location is accurate to within a quarter of a mile.

Geologic setting

Geologic description

The deposit at the Tomboy Ledge mine consists of a single 1- to 28-inch-wide quartz-carbonate vein in a shear zone that strikes N35E and dips 65W. The host rock is slate and siltstone of the Valdez Group of Late Cretaceous age, which here strikes N20E and dips 65NW (Nelson and others, 1985). Although not directly associated with the mineralization, numerous felsic dikes occur in the area (Hoekzema and Sherman, 1983). The vein contains arsenopyrite, pyrite, chalcopyrite, galena, and gold.
Johnson (1916) reported workings consisting of a 40-foot adit with a 20-foot winze, and a 35 -oot adit. The U.S. Bureau of Mines found a 105-foot adit (crosscut) with 40 feet of drift (Jansons and others, 1984).
The U.S. Bureau of Mines collected seven chip samples that contained a trace to 1.05 ounces of gold per ton and a trace to 0.02 ounce of silver per ton. They estimated reserves of 300 tons of ore containing 0.3 ounce of gold per ton and 0.06 ounce of silver per ton.
Recorded production is 219 ounces of gold and 9 ounces of silver (Jansons and others, 1984).
Geologic map unit (-148.362689496847, 60.8730112760426)
Mineral deposit model Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Cretaceous or younger; the vein cuts slate and siltstone of the Valdez Group of Late Cretaceous age.

Production and reserves

Workings or exploration
The deposit at this mine was discovered in 1912 by I. Westburg and J. Domenzet. In 1914 they drove a 40-foot adit with a 25-foot winze and a 35-foot adit (Johnson, 1914 [B 592-G, p. 233]). In 1982, an adit at 2,000 feet elevation was open (Jansons and others, 1984).
The U.S. Bureau of Mines visited the mine in 1981 (Hoekzema and Sherman, 1983). They mapped and sampled the adit located at 2,000 feet elevation. They collected a total of seven chip samples, three from the adit, and four from elsewhere on the property. The samples contained a trace to 1.05 ounces of gold per ton and a trace to 0.02 ounce of silver per ton.
Indication of production Yes; small
Reserve estimates The U.S. Bureau of Mines estimated a resource of 300 tons of ore having a grade of 0.3 ounce of gold per ton and 0.06 ounce of silver per ton (Jansons and others, 1984).
Production notes Total recorded production is 219 ounces of gold and 9 ounces of silver (Jansons and others, 1984).

References

MRDS Number A010557

References

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 3/9/2000