Iron Mask

Occurrences, Inactive

Alternative names


Commodities and mineralogy

Main commodities Au
Other commodities Cu; Pb; Zn
Ore minerals arsenopyrite; chalcopyrite; galena; gold; sphalerite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale SR
Quadrangle map, 1:63,360-scale C-7
Latitude 60.6649
Longitude -149.5904
Nearby scientific data Find additional scientific data near this location
Location and accuracy This map site is located in the SW1/4 section 26, T. 7 N., R. 2 W., of the Seward Meridian. It is situated at about 3,300 feet of elevation on the divide between Colorado and Fresno Creeks. This site represents two occurrences, the Iron Mask and the Mascot, which are mislocated on the 1951 Seward C-7 topographic map. This location is accurate to within a quarter of a mile. This is location 21 of Cobb and Richter (1972), locations 41 and 42 of Tysdal (1978 (MF-880-A)), location 29 of MacKevett and Holloway (1977), and location S-263 of Jansons and others (1984).

Geologic setting

Geologic description

This occurrence consists of two dikes, the Mascot and Iron Mask (Martin and others, 1915). The deposits in both dikes are auriferous, sulfide-bearing, quartz-calcite veins similar to those at the Gilpatrick Dike mine (SR136). The Mascot dike crops out at the head of the creek on a ridge between Colorado and Fox Creeks. This dike strikes north, dips vertically, and is traceable for several hundred feet. At the discovery monument, the dike is 40 inches wide; 3 feet to the east is a smaller dike that ranges from 3 inches to 1 foot wide (Martin and others, 1915). On the spur to the north, the main dike has split into six distinct stringers.
The Iron Mask dike crops out on the Colorado Creek slope between the Mascot dike and the Gilpatrick dike. It is 4 feet wide at the discovery monument. The mineralization of both dikes is similar to that in the Gilpatrick dike.
The quartz-calcite veins heal fractures in the felsic dikes and contain gold, arsenopyrite, galena, sphalerite and possibly chalcopyrite. The dikes are probably Eocene; the country rock is sedimentary strata of the Valdez Group of Late Cretaceous age (Tysdal, 1978 [MF-880-A]).
Geologic map unit (-149.592560563141, 60.6643303235361)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Eocene or younger; the dikes are probably Eocene in age.

Production and reserves

Workings or exploration There are mining claim discovery monuments on both dikes (Martin and others, 1915), but no workings are reported. The U.S. Bureau of Mines searched for the occurrences in 1980 but did not locate them (Hoekzema and Sherman, 1983).
Indication of production None


MRDS Number A010414


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 1/23/2000