Warner Bay

Prospect, Inactive

Alternative names

Prospect Bay

Commodities and mineralogy

Main commodities Ag; Au; Cu; Mo; Pb; Zn
Other commodities Sn; W
Ore minerals chalcopyrite; galena; gold; molybdenite; pyrite; sphalerite; wolframite
Gangue minerals calcite; chlorite; hematite; quartz; zeolites

Geographic location

Quadrangle map, 1:250,000-scale CG
Quadrangle map, 1:63,360-scale A-2
Latitude 56.15
Longitude -158.41
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is at or near sea level on the west side of Warner Bay just to the south of the spit (Berg and Cobb, 1967, locality 3; Cobb, 1972: MF-374; Cobb, 1980: OFR 80-909, locality 3; MacKevett and Holloway, 1977, locality 3; Cox and others, 1981, locality 11; Nokleberg and others, 1987, locality AP 9). Site location as plotted is accurate to within 1 mile.

Geologic setting

Geologic description

This prospect is within the northeast part of the Devils Bay batholith (Detterman and others, 1981). This pluton is a multiphase granodiorite to tonalite which intrudes sediments of the Cretaceous Hoodo Formation. Potassium-argon dates of the pluton indicate a range of between 5 and 10 million years (Wilson, 1980).
Atwood (1911) first described this prospect as a 50-foot wide crushed zone containing chalcopyrite, galena, pyrite, quartz and sphalerite. Later, more extensive investigation has shown that mineralization is exposed mostly in vertical cliffs extending down to sea level. Chalcopyrite and molybdenite occur as veinlets on joint surfaces spaced 5 to 10 centimeters apart (Cox and others, 1981). The extent of this mineralization has not been reported. Four samples collected by Resource Associates of Alaska in 1979 assayed as follows: 520 to 16,000 ppm copper, 280 to 9,110 ppm molybdenum, 0.4 to 2.5 ppm silver, 20 ppm tin, and 9-128 ppm tungsten. Cox and others (1981) list the grade of this mineralization at 0 to 0.07 percent molybdenum with a trace of copper. Nokleberg and others (1987) list an average grade of 0.03 percent copper with values up to 0.7 percent.
Massive sulfide veins, ranging in width from 2 inches to 4 feet occur filling a northwest-trending nearly vertical fracture system. These are spaced approximately 100 feet apart over a distance of 3500 feet along the beach. Assays of this material by Resource Associates of Alaska returned values of up to 5.7 percent copper, 0.312 ounce gold per ton, 0.91 percent molybdenum, 1.25 percent lead, 395 ppm tungsten, and 10.8 percent zinc (Anderson and others, 1979). One sample reported 3000 ppm lanthanum.
A breccia pipe, approximately 3 meters in diameter, occurs at the extreme north end of the showing. It contains clasts of propylitically altered granodiorite cemented by galena, pyrite, sphalerite, calcite, chlorite, and zeolites. The small tonnage in sight is estimated at more than 10,000 tonnes. Anderson and others (1979) give values for a high-grade sample as follows: 1600 ppm copper, 0.1 ppm gold, 4000 ppm lead, 2.3 ppm silver, 8 ppm tungsten, 400 ppm zinc.
Four holes were drilled on the prospect in 1965 and 1966 by Pan American Exploration (now Amoco) for a total of 2432 feet Cobb (1980: OFR 80-909) reports drilling as recent as 1977.
Geologic map unit (-158.412027940191, 56.1492213866075)
Mineral deposit model Porphyry copper-molybdenum; polymetallic vein (Cox and Singer, 1986; models 21a, 22c).
Mineral deposit model number 21a, 22c
Age of mineralization The age of mineralization is estimated at less than 6.5 million years (Wilson, 1980).
Alteration of deposit Alteration of granodiorite host rock is limited to partial alteration (?) of amphibole to biotite and slight chloritization of biotite. Clasts of granodiorite in the breccia pipe exhibit propylitic alteration. Biotitic and sericitic alteration occur as thin selvages along veinlets.

Production and reserves

Workings or exploration Two short adits were driven in the early 1900s (Atwood, 1911). In the 1960s four holes were drilled for a total of 2432 feet. Some drilling has been reported as late as 1977. Bear Creek Mining Company visited the property in 1975 and Resource Associates mapped and sampled there in 1979.
Indication of production None

Additional comments

This site is located on land patented by or interim conveyed to the Bristol Bay Native Corporation.

References