The most productive mines and most of the significant prospects on western Chichagof Island are in the approximately 4-square-mile area centered on Doolth Mountain that extends from Klag Bay to south of Kimshan Cove (Reed and Coats, 1941; Bittenbender and others, 1999). The rocks in the area are Cretaceous Sitka Graywacke that consists of massive, thick-bedded, and slaty graywacke, locally interbedded with lenticular layers of recrystallized basalt ('greenstone') (Johnson and Karl, 1985). The strata generally strike northwest and dip steeply southwest. They are intruded by felsic and mafic dikes, but no granitic plutons are exposed in the area. All of the rocks are regionally metamorphosed to prehnite-pumpellyite grade, and some of the dikes are silicified near the orebodies (Reed and Coats, 1941).

The principal structures in the area are numerous northwest-striking, steeply-dipping faults. Two of them, the Hirst and Chichagof faults, along with splays ('splits') from them, localized the principal orebodies, particularly where variations at the intersections of faults and the bedding created potential openings that allowed increased fluid migration and mineralization (Bittenbender and others, 1999).

The deposits are auriferous quartz veins containing pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, and native gold, most of which is free-milling. The quartz is accompanied by a little calcite, and a little gold occurs in the wallrocks of the veins. The productive veins feature ribbon structure, characterized by graphitic partings, and the veins commonly are accompanied by graphitic gouge. Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler, 1995; Goldfarb, 1997; Goldfarb and others, 1997).

The Chichagof Mine opened in 1905, and from 1906 to 1942 it produced 660,000 ounces of gold and 195,000 ounces of silver from more than 600,000 tons of ore (Reed and Coats, 1941; Still and Weir, 1981; Bittenbender and others, 1999). The mine closed in 1942, but small amounts of tailings were reworked from 1942 to 1973. The mine and adjacent area are covered by 29 patented claims. In 1978 and 1979, the U.S. Bureau of Mines examined the surface and accessible underground workings (Still and Weir, 1981). They describe the ore zones as irregular bodies whose long dimension plunges south and whose short dimension is parallel to their northwest strike. The ore zones are up to 15 feet wide, 1,000 feet in strike length, and 1,800 feet high. One 14-foot stope averaged 6 ounces of gold per ton, but the average ore tenor for the life of the mine was 1.0 ounce of gold per ton. Mining reached a depth of 2,700 feet below sea level. The underground workings extended along the Chichagof Fault for 4,800 feet in a horizontal direction and 4,300 feet vertically, and twenty-three percent of the workings were mined. The workings, almost all of which are inaccessible, included an adit with 5 levels totaling 9,950 feet, and 6 shafts to a depth of 2,750 feet below sea level.

The U.S. Bureau of Mines estimated the resources to be 76,600 tons of material with an average grade of 0.4 ounce of gold per ton; 463,000 tons with an average grade of 0.30 ounce of gold and 0.09 ounce of silver per ton; and 456,000 tons of tailings with an average grade of 0.11 ounce of gold and 0.03 ounce of silver per ton (Still and Weir, 1981).