Prospect, Inactive

Commodities and mineralogy

Main commodities Ag; Au
Other commodities As; Cu; Hg; Pb; Sb; Zn
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrite; sphalerite; tetrahedrite
Gangue minerals chalcedony; quartz

Geographic location

Quadrangle map, 1:250,000-scale PM
Quadrangle map, 1:63,360-scale B-3
Latitude 55.307
Longitude -160.728
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is located on western Unga Island approximately 1.5 miles west of the head of Zachary Bay (MacKevett and Holloway, 1977, locality 16; Wilson and others, 1988, locality 16). The map site is at an elevation of 1,100 feet, 0.25 mile south-southwest of peak 1965. The location is accurate.

Geologic setting

Geologic description

This prospect is in volcanic rocks of the late Oligocene to middle Miocene Unga Formation (Wilson and others, 1995). The rocks include volcanic flows, tuffs, ash-flow tuffs, volcaniclastic rocks, and hornblende porphyry.
Anomalous gold and silver values have been traced in surface samples for more than 2,300 feet (Peterson and others, 1982; 1983). A northwest-trending mineralized breccia zone appears to have controlled high-grade ore shoots where it intersects northeast-trending structures. The host for the gold-silver mineralization is volcanic breccia. The breccia varies from fractured silica- veined rock to a polymictic breccia, that may in part be intrusive. The highest grade mineralization is associated with the polymictic breccia. The mineralization is accompanied by intense silicification and pyritization. Sparse amounts of arsenopyrite(?), chalcopyrite, galena, sphalerite, and tetrahedrite occur locally.
The highest precious metal values were obtained from the discovery outcrop, where samples assayed 4.75 ppm gold and 268 ppm silver (Peterson and others, 1982; 1983). One drill hole intersected 33 feet of breccia containing 1.26 ppm gold and 11.7 ppm silver. This intersect includes 6 feet of breccia containing 2.38 ppm gold and 16.5 ppm silver. Several other holes cut rock having lower grade precious metal values. Surface exposures of other mineralized breccia returned values of as much as 4.69 ppm and 1.47 ppm gold.
Geologic map unit (-160.730034702149, 55.3061697720747)
Mineral deposit model Epithermal gold veins
Age of mineralization Oligocene or younger.
Alteration of deposit Alteration locally is zoned outward from silicic to argillic to propylitic. The silicified zones contain quartz veins, amethystine quartz, chalcedony, massive quartz, and pyrite. Argillic minerals include montmorillonite, illite, and a green chloritic clay containing 1 to 10 percent pyrite (Peterson and others, 1982; 1983).

Production and reserves

Workings or exploration In 1983 Unc Teton Exploration Drilling Company drilled six core holes for a total of 1,350 feet, cut 475 feet of trenches, ran 12,350 feet of VLF-EM surveys, collected more than 400 samples of various types for geochemical analysis, and did 20,000 feet of gridding. The U.S. Geological Survey collected a few samples of this deposit in the mid-1980s. Battle Mountain Exploration Company examined the prospect in 1986.
Indication of production None

Additional comments

This prospect is on land patented by, or interim-conveyed to, the Aleut Corporation.


MRDS Number 10308123


Peterson, R.J., Handverger, P., Rosenkrans, D., Bartels, E, and Woolston, D., 1983, Shumagin Islands precious metal exploration program southwest Alaska: UNC Teton Exploration Drilling Company report, 61 p. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Peterson, R.J., Lemmers, J., Handverger, P., Gallagher, J., Pilcher, R., East, J., Macleod, T., Bartels. E., 1982, Geology and precious metals potential Unga, Popof, and Korovin Islands, Shumagin Group, Aleutian Chain, Alaska: UNC Teton Exploration Drilling Company report, 127 p., 5 map sheets, various scales. (Report held by the Aleut Corporation, Anchorage, Alaska.)
Reporters S.H. Pilcher
Last report date 1/4/2001