Unnamed (south of Zachary Bay)

Prospect, Inactive

Commodities and mineralogy

Main commodities Au; Cu
Other commodities Mo
Ore minerals chalcocite; chalcopyrite; molybdenite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale PM
Quadrangle map, 1:63,360-scale B-2
Latitude 55.254
Longitude -160.633
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is located on Unga Island approximately 2 miles south of Zachary Bay (Christie, 1974, color anomaly 92; Wilson and others, 1988, locality 48). The map site is at an elevation of 700 feet, about 0.4 mile west of the enter of sec. 3, T. 57 S., R. 75 W., Seward Meridian. The location is accurate to within 1,000 feet.

Geologic setting

Geologic description

This prospect is marked by a color anomaly measuring 2,000 by 5,000 feet. The rocks consist of a series of andesitic volcanic rocks and interbedded volcanic sediments intruded by quartz diorite and feldspar porphyry. A diorite plug forms the core of the anomaly. The diorite is only slightly altered and contains 1 percent disseminated pyrite. Andesites in contact with this intrusive carry pyrite and a trace of chalcopyrite. The volcanic rocks belong to the late Eocene to early Oligocene Popof volcanic rocks (Wilson and others, 1995). A potassium argon date on sericite from the diorite was determined to be 14.6 Ma (Wilson and others, 1994).
Copper-gold mineralization occurs in scattered outcrops in an area (including cover) 4,000 feet in diameter. Chalcopyrite is the only primary copper mineral. The other primary sulfides are pyrite and molybdenite. Chalcocite is generally present in outcrops containing 500 ppm copper or greater. The main showing consists of 150 feet of hornfels containing 0.36 percent copper, 0.004 percent molybdenum, 0.08 ounce of silver per ton, and 0.16 ounce of gold per ton (Christie and Richards, 1974). Peripheral outcrops contain much lower metal values.
Approximately 600 feet northeast of the main showing, an outcrop of quartz-veined and pyritic feldspar porphyry carries as much as 0.76 percent copper and 0.10 ounce of gold per ton. The sulfides at this outcrop have been almost totally leached. An outcrop to the south carries as much as 1,720 ppm copper (Dircks and Richards, 1976). Three of four holes drilled in 1975 penetrated only short intervals grading 0.1 percent copper. The other hole was drilled through 383 feet grading 0.11 percent copper and 0.28 ppm gold.
Geologic map unit (-160.635043517028, 55.2531697342329)
Mineral deposit model Porphyry Cu, Porphyry Cu-Au (Cox and Singer, 1986; models 17, 20c)
Mineral deposit model number 17, 20c
Age of mineralization Miocene or younger.
Alteration of deposit
Propylitic alteration consisting of various combinations of epidote, chlorite, pyrite, and magnetite is widespread. Quartz-sericite-pyrite, magnetite-plagioclase, and potassic (biotite) assemblages are also present.
Alteration zoning is poorly understood due primarily to lack of outcrop. One zoning sequence of increasing intensity consists of epidote-pyrite to chlorite-pyrite to chlorite-magnetite.

Production and reserves

Workings or exploration
This prospect was mapped and sampled by an Aleut-Quintana-Duval joint venture in 1974. They collected more than 150 rock, silt, and soil samples. In 1975 they conducted a magnetometer survey and drilled four holes for a total of 955 feet. They reported channel samples assays of 0.36 percent copper, 0.004 percent molybdenum, 0.016 ounce of gold per ton, and 0.08 ounce of silver per ton over 150 feet. Drill hole Z-1 intersected 383 feet grading 0.11 percent copper and 0.28 ppm gold.
Resource Associates of Alaska relogged, split, and assayed the core in 1981. They were interested primarily in gold values. The results were not encouraging (Trujillo and others, 1981). Battle Mountain Exploration company briefly sampled the area in 1986.
Indication of production None

Additional comments

This prospect is located on land selected by the Aleut Corporation.

References

MRDS Number 10308130

References

Christie, J.S., 1974, Aleut-Quintana-Duval 1974 joint venture, final report: Unpublished Quintana Minerals Corporation report, 24 p., 3 appendices, 2 maps. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Christie, J.S., 1975, Aleut-Quintana-Duval 1975 joint venture, preliminary report: Quintana Minerals Report, 6 p., 9 map sheets, scales 1:63.360 and 1 inch equals 800 feet. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Christie, J.S., and Richards, G.G., 1974, Zachary Bay color anomaly and copper-gold prospect Unga Island Alaska, Port Moller B-2 quadrangle: Quintana Minerals Report, 9 p. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Dircks, N.J., and Richards, G.G., 1976, Final report on Zachary Bay project Unga Island, Alaska Port Moller B-2 quadrangle: Quintana Minerals, 10 p. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Trujillo, R.S., Andersen, G.D.,, MacLeod, T., Hendrick, K., Farnham, S., Peterson, J., 1981. Exploration and evaluation of the Unga-Popof-Korovan Islands portion of lands leased from Aleut Native Corporation: Resource Associates of Alaska report, 70 p., 38 map sheets, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Reporters S.H. Pilcher
Last report date 1/18/2001