Weasel Mountain

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu; Mo
Other commodities Ag; Au; Pb; Zn
Ore minerals chalcopyrite; galena; molybdenite; pyrite; sphalerite
Gangue minerals calcite; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale CG
Quadrangle map, 1:63,360-scale B-1
Latitude 56.49
Longitude -158.19
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is located approximately 2 miles northwest of Weasel Mountain and 2 miles west of Hook Bay in T. 42 and 43 S., R. 56 and 57 W., of the Seward Meridian (Cox and others, 1981, locality 4; MacKevett and Holloway, locality 25?). Location is accurate to within 1 mile.

Geologic setting

Geologic description

The area of this site is underlain by strata of the Cretaceous Chignik Formation and by the interbedded sediments, volcaniclastics, and andesite of the Oligocene-Pliocene Meshik Formation.
Fields (1977) describes two major intrusive systems, a diorite porphyry dike or sill and a younger quartz porphyry mass. The diorite is approximately 1/2 mile in width and extends in a northeast direction for more than a mile. The quartz porphyry intrudes the the diorite, extends in a northeast direction, and measures approximately 700 by 3000 feet in outcrop. Butherus (1981) reports these intrusive phases as occupying approximately two square miles. Large areas of hornfels have resulted from thermal metamorphism of the nearby sedimentary rock.
The site is marked by a color anomaly which contains 1 to 6 percent sulfides over an area 2 miles in long by 1 mile wide. Fields (1977) describes the sulfides as mostly fracture controlled, primarily along certain marginal zones of the diorite and quartz porphyry and in the metasediments to the west. Chalcopyrite and sparse molybdenite occur in the marginal areas of the diorite, mostly along northeast-trending fracture zones. The resulting copper anomaly is approximately 700 by 1500 feet and contains 500 to 2100 ppm copper. The molybdenum anomaly coincides in part with the copper but has a more easterly trend. This anomaly is approximately 1000 by 2000 feet and contains 22 to 160 ppm molybdenum. Low gold values (0.04 to 0.18 ppm) coincide with the molybdenum. Diffuse peripheral lead-zinc values are present.
Alteration is diffuse with no strong focus on a core. A broad sericitic zone exists within the area of higher sulfide content. Sericite occurs pervasively and along fractures. Propylitic alteration in the sediments is patchy and consists of chlorite and epidote clots.
Butherus (1981) reports intrusive breccia near the head of a valley in the NW1/4 sec. 2, T. 43 S., R. 57 W., of the Seward Meridian. The breccia, approximately 800 feet in diameter, contains traces of chalcopyrite and sphalerite in a quartz-tourmaline matrix. Other minerals present include pyrite, calcite, and barite. One sample contained greater than 10,000 ppm copper, 0.06 ppm gold, 13 ppm lead, 28 ppm silver, and 1800 ppm zinc. Three other samples contained up to 750 ppm copper, 0.02 to 0.04 ppm gold, and 1.2 to 11.4 ppm silver.
Geologic map unit (-158.192045765312, 56.4892257252411)
Mineral deposit model Porphyry copper; porphyry copper-molybdenum (Cox and Singer, 1986; models 17, 21a).
Mineral deposit model number 17, 21a
Age of mineralization Tertiary.
Alteration of deposit Alteration consists of a broad sericitic zone within the area of higher sulfide content and a peripheral, patchy propylitic zone.

Production and reserves

Workings or exploration
Bear Creek Mining Company mapped and sampled this occurrence in 1975-1976, and Resource Associates of Alaska explored it in 1979 and 1981.
Copper values of 500 to 2100 ppm occur in an area of 700 by 1500 feet. Molybdenum values of 22 to 160 ppm occur in an area of 1000 by 2000 feet. Gold values are up to 0.18 ppm.
Indication of production None

Additional comments

This site is partially on land selected by the Bristol Bay Native Corporation.


MRDS Number A012445
Reporters S.H. Pilcher (Anchorage)
Last report date 2/8/2000