Unnamed (near hill 2825 on Granite Mountain)

Occurrence, Inactive

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale B-2
Latitude 62.31799
Longitude -156.73239
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 2,600 feet, about 0.7 mile southwest of peak 2923, the top of Granite Mountain. It is about 0.3 mile north of the center of section 29, T. 26 N., R. 40 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

This occurrence, also referred to as the Granite Mountain prospect (Bundtzen and Miller, 1997) consists of several sizable bodies of metasomatic axinite, anatase, and tourmaline at the contact between the Granite Mountain pluton and hornfelsed rocks derived from the Upper cretaceous Kuskokwim Group. The occurrence includes: 1) zones of tourmaline-bearing sheeted veins, 2) tourmaline-cemented breccias in hornfels; and 3) axinite-tourmaline-sulfide replacement bodies in both intrusive rocks and in hornfels. The nearby Granite Mountain pluton has a 40K/40Ar age of 62.6 Ma (Bundtzen and Miller, 1997).
One large area of boron-rich tourmaline-axinite-anatase greisen is 1,300 feet long, about 50 feet wide, and cylindrical in cross section; it may contain 5.5 million tons of boron-enriched material of unknown grade. This zone also contains disseminated gray sulfide minerals. Grab samples from the occurrence contained 100 parts per million (ppm) tin, 500 parts per billion (ppb) silver, 50 ppb gold, 9.0 ppm bismuth, 28 ppm antimony, 80 ppm arsenic, and more than 2,000 ppm boron (McGimsey and others, 1988; Bundtzen and Miller, 1997).
Geologic map unit (-156.734769880698, 62.317322682835)
Mineral deposit model Sn-polymetallic deposit or Polymetallic vein (Cox and Singer, 1986; model 20b or 22c).
Mineral deposit model number 20b or 22c
Age of mineralization The nearby Granite Mountain pluton has a A 40K/40Ar age of 62.6 Ma (Bundtzen and Miller, 1997).
Alteration of deposit Development of axinite-tourmaline-quartz greisen.

Production and reserves

Workings or exploration Samples were collected by the U.S. Geological Survey and Alaska Division of Geological and Geophysical Surveys in 1984 (McGimsey and others, 1988; Bundtzen and Miller, 1997).
Indication of production None