Mount Coxcomb

Prospect, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag
Ore minerals chalcopyrite; pyrite
Gangue minerals chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale UN
Quadrangle map, 1:63,360-scale C-2
Latitude 53.8846
Longitude -166.476
Nearby scientific data Find additional scientific data near this location
Location and accuracy Mineralized area on the northwest side of Mount Coxcomb extends for approximately 2 km along coast of Iliuliuk Bay, immediately southwest of Summer Bay and extends into Summer Bay on its west side. Equivalent to anomaly no. 17 of Christie (1974).

Geologic setting

Geologic description

Alteration and mineralization occurs in rocks of the Unalaska Formation (see Drewes and others, 1961), composed of volcanic breccia, volcaniclastic sedimentary rocks, debris flows, and rare lava flows. The dominant lithology within the altered zone appears is regionally propylitized andesitic tuff and flows (Randolph, 1991). A number of hypabyssal dioritic stocks, possibly cupolas related to emplacement of the Captain's Bay pluton, intrude the prospect areas. Emplacement of the stocks generated hydrothermal systems, which filled structures and fractures with cockscomb quartz, presumably related to stock emplacement (Randolph, 1991). Randolph (1991) reports two styles of mineralization at Mt. Coxcomb. Most common is a wide-spaced quartz vein system characterized by scattered emplacement of non-brecciated comb quartz over a large area. Veins fill open space fractures, 3 inches to 3 feet (0.7 to 1 m) wide, 10 to 20 feet (3 to 6 m) long, spaced a few to tens of feet apart. Veining is spatially related to hypabyssal stocks and faulting. Ore grade gold is restrict to the quartz veining. The veins occasionally yield pyrite or arsenopyrite, but have low silver, mercury, and base metal values. The second style of mineralization is in large-scale vein systems that are composite emplacement of brecciated cockscomb quartz along major structural breaks. The structures are typically 10 to 40 feet (3 to 12 m) thick and more than 1,000 feet (300 m) long. These display no wall rock alteration, except for silicification within the anastomosing zones. Gold values can reach or grade, silver, mercury and arsenic are only weakly anomalous and the veins are sulfide-free.
Geologic map unit (-166.477896644063, 53.8837375634403)
Mineral deposit model Epithermal gold vein; disseminated gold
Mineral deposit model number 25
Age of mineralization Late Tertiary or younger
Alteration of deposit Regional propylitic alteration overprinted by silicic and sericitic alteration is common, as is the introduction of pyrite throughout the altered volcanic breccia. Area is highly iron-stained, apparently derived from weathering of pyrite.

Production and reserves

Workings or exploration Battle Mountain Exploration Co. (BMEC) established three sampling grids over part of area. The C1 and C3 grids were located on wide-spaced vein systems as described above although a zone of the large-scale vein system also crosses the C1 grid. The C1 grid produced gold values to 776 ppb and first-pass gold-in-rock values of 0.36 oz/t (12 ppm) and greater than 50 ppm arsenic; mineralization appeared to be restricted to wide-spaced cockscomb quartz veins and not to pervasively silicified or 'crackle-brecciated' tuffs. A geophysical survey of the grid indicated a major north dipping mineralizing structure, localized on a mapped fault, runs through the grid. Channel sampling along the trend outlined at least 322 feet (100 m) of 0.06 oz/t gold. The C2 grid produced no significant gold values. The C3 grid, located approximately 1 km north of the C1 grid, yielded significantly higher gold-in-soil than C1 at 3,500 ppb and significantly lower arsenic than the C1 grid. Sampling of quartz veins produced gold and silver values as high as 2.932 oz/t (102 ppm) and 14.3 ppm. A geophysical survey outlined a NNW-trending anomaly within the north central portion of the grid. Rock sampling along this anomaly averaged 0.75 oz/t (26 ppm) gold and defined an open-ended trend measurely roughly 100 by 200 feet (30 by 60 m). BMEC reported that gold had been panned in the vicinity of Mt. Coxcomb since before 1900 and BMEC mapping crews found several prospect pits and tunnels in the area.
Indication of production Undetermined

Additional comments

At north end of altered zone, along Summer Bay road, the ruins of what may have been a tramway come down a steep gully. During WWII, Mount Coxcomb was the site of a major shore battery and the tramway may be related to that installation rather than any workings.

References

MRDS Number A106000

References

Christie, J.S., 1974, Aleut-Quintana-Duval 1974 joint venture, final report: Unpublished Quintana Minerals Corporation report, 24 p., 3 appendices, 2 maps. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Randolph, D.B., 1991, Unalaska project, 1990 final report: Battle Mountain Exploration Company, Alaska District, 62 p., 5 appendices, 15 plates, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Reporters F.H. Wilson
Last report date 5/6/1996