Unnamed (southwest Granite Mountain)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Sn
Other commodities As; B; Bi; Pb; Sb
Ore minerals cassiterite
Gangue minerals tourmaline

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale B-2
Latitude 62.31214
Longitude -156.75261
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is about 1.4 mile southwest of the peak 2923, the top of Granite Mountain, at an elevation of about 2,300 feet. It is about 0.5 mile east-southeast of the center of section 30, T. 26 N., R. 40 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

This occurrence consists of a extensive zone of cassiterite-bearing, tourmaline-axinite greisen that may be a southwest extension of the similar occurrence to the northeast (ID146) (Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). Tourmaline-rich quartz porphyry and brecciated tourmaline-axinite-cemented hornfels occurs in the cupola zone of the 62.6 Ma, Granite Mountain pluton (Miller and Bundtzen, 1994). Bundtzen and Miller (1997) identified disseminated cassiterite in one sample; however, no sulfides or sulfosalts were observed. Grab samples of mineralization contained up to 300 parts per million (ppm) tin, 7,000 parts per billion (ppb) silver, 500 ppm lead, 54 ppm antimony, 100 ppm arsenic, 54 ppm bismuth, and more than 2,000 ppm boron (McGimsey and others, 1988).
Geologic map unit (-156.75499103074, 62.311471503144)
Mineral deposit model Sn-polymetallic deposit (Cox and Singer, 1986; model 20b).
Mineral deposit model number 20b
Age of mineralization Undated; probably related to the nearby Granite Mountain pluton that has an age of 62.6 Ma (Bundtzen and Miller, 1997).
Alteration of deposit Development of tourmaline-axinite 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).
Indication of production None