Windy Bay

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu; Mo
Other commodities Au; Pb; Zn
Ore minerals chalcopyrite; galena; gold; molybdenite; pyrite; pyrrhotite; sphalerite
Gangue minerals chlorite; quartz

Geographic location

Quadrangle map, 1:250,000-scale CG
Quadrangle map, 1:63,360-scale A-3
Latitude 56.143
Longitude -158.779
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is approximately 2 miles west of the head of the north arm of Windy Bay and includes the headwaters of streams draining into that head of the bay (Cox and others, 1981, locality 9). The site is accurate as plotted.

Geologic setting

Geologic description

The geologic setting at this site consists of a quartz diorite stock which has intruded sedimentary units of the Jurassic Naknek Formation (Fields, 1977). These units include grits, graywacke, siliceous siltstone, and black shale.
A discontinuous color anomaly is present along the inferred contact zone (Fields, 1977). The sediments near the contact have been hornfelsed and contain pyrrhotite, pyrite, rare chalcopyrite, and magnetite as disseminations and as veinlet and fracture fillings. Total sulfide content is 1-5 percent. Sulfides occur up to 1000 feet from the contact.
The sulfide content of the intrusive is 1 percent or less. Chalcopyrite is present on fracture surfaces and in quartz-chlorite and pyrite veinlets. These strike approximately N 25 W and cover an area of 1000 by 4000 feet.
Samples of the mineralized intrusive contained up to 424 ppm copper, 0.13 ppm gold, 32 ppm lead, 25 ppm molybdenum, and 9 ppm zinc (Fields, 1977).
The intrusive exhibits local chloritization along with scattered patches of epidote and secondary biotite. The hornfelsed sediments have been silicified and contain secondary biotite and minor chlorite.
Geologic map unit (-158.781016871225, 56.1422138672518)
Mineral deposit model Porphyry copper; porphyry copper-gold; porphyry copper-molybdenum (Cox and Singer, 1986; models 17, 20c, 21a).
Mineral deposit model number 17, 20c, 21a
Age of mineralization Tertiary.
Alteration of deposit Alteration in the intrusive consists of local zones containing chlorite, epidote, and secondary biotite. The sediments near the intrusive contact have been hornfelsed, silicified, and contain chlorite and secondary biotite.

Production and reserves

Workings or exploration
Bear Creek Mining Company briefly explored this site during the period 1975-1976. The few samples collected contained up to 424 ppm copper, 0.13 ppm gold, 32 ppm lead, 25 ppm molybdenite, and 9 ppm zinc (Fields, 1977).
Resource Associates of Alaska briefly sampled this occurrence in 1979 (Anderson and others, 1979).
Indication of production None

Additional comments

This site is partially on land selected by the Bristol Bay Native Corporation. The remainder is within the Alaska Peninsula National Wildlife Refuge.

References

MRDS Number A012450
Reporters S.H. Pilcher (Anchorage)
Last report date 2/8/2000