Prospect, Undetermined

Commodities and mineralogy

Main commodities Au
Other commodities As
Ore minerals arsenopyrite; gold; pyrite
Gangue minerals calcite or dolomite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale A-5
Latitude 57.2098
Longitude -135.5478
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Krestof prospect is at sea level on the northwest coast of Krestof Island, about a mile south of the Sound Islands. The prospect is at the southeast corner of sec. 3, T. 54 S., R. 62 E. It is location P-107 of Bittenbender and others (1999) and MAS no. 0021140052 (U.S. Bureau of Land Management, 2002). The location is accurate.

Geologic setting

Geologic description

The Krestof prospect was discovered in 1937 from gold-bearing float along the beach. It was optioned to the Hirst-Chichagof Mining Company who brought a small diamond-drill to the property and drilled a few holes in 1938 (Roehm, 1938 [PE 114-12]; Smith, 1939 [B 910-A]; Smith, 1939 [B 917-A]). The results of the drilling were not encouraging and the property was dropped by 1939. Apparently there has been no work on the property since.
The rocks in the vicinity are part of the Jurassic and Cretaceous, Sitka Graywacke which is mainly graywacke and argillite that in this area has been hornfelsed by a nearby Tertiary granodiorite intrusion to the south (Loney and others, 1975). The rocks generally strike N45W and dip 60-70NE.
The deposit consists of three showings about 1,500 feet apart (Roehm, 1938 [PE 114-12]). One showing consists of three quartz veins No 1 vein is exposed for 80 feet and passes into water at both ends. It strikes N60E, dips 60SE, and is 4 to 6 inches thick. No 2 vein is exposed in a trench for 50 feet. It strikes N55E, dips 70NW, and is 6 to 8 inches thick. No. 3 vein is exposed for 35 feet; it strikes N83E and dips nearly vertically. At another showing, a small banded quartz vein up to 7 inches thick is exposed for 300 feet in five trenches. Numerous quartz boulders also occur along the beach nearby and there are several exposures of quartz stringers that are exposed in graywacke and argillite along the beach. All of the veins consist mainly of slightly-banded, white milky quartz with minor amounts of calcite or dolomite, sericite, and altered pieces of wallrock. The veins commonly contain small amounts of arsenopyrite, pyrite, and visible gold. Roehm (1938 [PE 114-12]) collected 3 samples 6 to 8 inches long across the veins. they contained nil to 0.03 ounce of gold per ton and nil silver.
Bittenbender and others (1999) collected 3 samples of quartz vein material and sheared graywacke; one had 1 percent arsenopyrite. The samples contained 45 to 8,050 parts per billion gold.
Geologic map unit (-135.54957111209, 57.2094449772965)
Mineral deposit model Low-sulfide gold-quartz veins (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization Jurassic or younger based on the age of the host rock.
Alteration of deposit The wallrocks are at least locally altered.

Production and reserves

Workings or exploration The veins were explored by several trenches and a few holes were diamond drilled in 1938.
Indication of production None