Unnamed (eastern Chuilnuk Mountains)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Bi; Sn
Other commodities As; Au; Sb
Ore minerals unspecified sulfides
Gangue minerals quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale SM
Quadrangle map, 1:63,360-scale B-5
Latitude 61.31543
Longitude -157.74869
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is in the eastern Chuilnuk Mountains, in the headwall cirque of an unnamed tributary of the Chuilnuk River. It is at an elevation of about 2,700 feet, about 0.6 mile east of peak 3310 and 0.6 mile north-northwest of peak 3110, in the SW1/4 sec. 8, T. 14 N., R. 47 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

This occurrence consists of a series of quartz-tourmaline-sulfide-bearing greisen veins in the 68-Ma-old Chuilnuk Mountains pluton (Cady and others, 1955). The Chuilnik Mountains pluton is a mesozonal intrusion composed of medium-grained, hornblende-biotite granodiorite that intrudes shale and sandstone of the Upper Cretaceous, Kuskokwim Group (Decker and others, 1995).
The veins vary from 1 to 4 inches thick and occur at a density of about 1 vein per foot. The sulfide content of the veins is low, less than 2.0 percent, but tourmaline makes up as much as 20 percent of the vein material. The greisen veins can be traced perpendicular to its strike for about 1,300 feet across the cirque headwall. Individual veins strike N5-15E and dip nearly vertically and they extend up the headwalls of the cirque here for at least 300 feet. Two grab samples of the veins collected at the base of the cirque contained up to 63 parts per billion (ppb) gold, 2,300 ppb silver, 515 parts per million (ppm) arsenic, 405 ppm bismuth, 59 ppm antimony, and 123 ppm tin (T. K. Bundtzen, unpublished data, 1998).
Geologic map unit (-157.751028746555, 61.314724604833)
Mineral deposit model Silver-polymetallic veins or tin veins (Cox and Singer, 1986; models 20b or 15b).
Mineral deposit model number 20b or 15b
Age of mineralization Unknown. Decker and others (1995) report a 40K/40Ar biotite age of 68 Ma for the Chuilnuk Mountains pluton.
Alteration of deposit Development of tourmaline-quartz-sulfide greisen.

Production and reserves

Workings or exploration The geology of the Chuilnik Mountains area was mapped by the U.S. Geological Survey in the 1940s and by the Alaska Division of Geological and Geophysical Surveys in the 1980s (Cady and others, 1955; Decker and others, 1995). This occurrence was discovered in 1998 (T.K. Bundtzen, unpublished data, 1998).
Indication of production None