Prospects, Undetermined

Alternative names

East Ako
West Ako
Ako Saddle

Commodities and mineralogy

Main commodities As; Au; Cu; Mo
Other commodities Bi; Sb; W
Ore minerals arsenopyrite; chalcopyrite; gold; molybdenite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale BH
Quadrangle map, 1:63,360-scale B-2
Latitude 60.2802
Longitude -159.6964
Nearby scientific data Find additional scientific data near this location
Location and accuracy The exact locations of these three prospects is uncertain but they are generally along the western margin of the Crooked Mountain pluton between the upper parts of Swift and Akoswift Creeks. The likely center of these prospects is about 2.3 miles northeast of the center of (unnamed) lake 2050 on Akoswift River, and about 0.5 mile east-northeast of the center of section 9, T. 2 N., R. 60 W., of the Seward Meridian. The location is accurate to within a mile.

Geologic setting

Geologic description

The three prospects of this site are along the western margin of the Late Cretaceous, Crooked Mountain pluton, which has been dated at 69.8 Ma (Box and others, 1993). This composite pluton is about 10 kilometers in diameter. Its core of biotite granodiorite and granite is rimmed by a shell of gabbro and diorite. The pluton is bordered to the west by Late Cretaceous volcanic rocks and tuff that are hornfelsed near its contact.
The Ako prospects were found in the the late 1980s during a regional geochemical survey (Gold Crest Mines Inc., 2011 [summary]). They generally are associated with anomalous arsenic, antimony, bismuth and tungsten, and by iron-stained color anomalies.
The mineralization at the East Ako prospect consists of disseminated, fracture-controlled, and stockwork-veined zones in the Crooked Mountain pluton (Gold crest Mines Inc., 2011 [antimony]; Gold Crest Mines Inc., 2011 [gold]). Several zones of arsenopyrite-quartz veins with sparse molybdenite and chalcopyrite are well exposed. The veins are accompanied by argillic, propylitic, silic, and potassic alteration. The mineralization can be traced for about 150 meters and is up to 75 meters wide.
The mineralization at the West Ako prospect consists of intense biotite alteration, potassium-feldspar flooding, silicification, and quartz-sulfide stockworks along a resistant 'rib' in the pluton. The mineralized zone is 10 to 20 meters thick and can be traced for about 100 meters. Samples across 3 to 5 meters contained up to 0.4 gram of gold per tonne (Gold Crest Mines Inc., 2011 [rock samples]).
The Ako Saddle prospect coincides with a extensive rusty-orange color anomaly. Samples of pyritic, sericite-altered granodiorite had anomalous gold values.
Geologic map unit (-159.698651181925, 60.2794600246385)
Mineral deposit model Polymetallic veining and stockworks in the periphery of a granitic pluton.
Age of mineralization Late Cretaceous or younger. The veins cut a 69.9 Ma granitic pluton and may be genetically related to it.
Alteration of deposit The East Ako mineralization is accompanied by argillic, propylitic, silic, and potassic alteration. The West Ako mineralization is accompanied by intense biotite alteration, potassium-feldspar flooding, and silicification.

Production and reserves

Workings or exploration Several episodes of mapping and sampling from 1988 to 2007. Covered by regional geochemical and geophysical surveys.
Indication of production None


Reporters D.J. Grybeck (Contractor, USGS)
Last report date 2/28/2011