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. |