Greisen

Prospect, Inactive

Commodities and mineralogy

Main commodities Ag; Pb; Zn
Other commodities As; Cu; Hg; Sb; Sn; W
Ore minerals galena; scheelite
Gangue minerals axinite; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale SM
Quadrangle map, 1:63,360-scale D-7
Latitude 61.77006
Longitude -158.45663
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Greisen prospect is at an elevation of 2,900 feet on the ridge north of the head of Jungjik Creek. It is in the NW 1/4 sec. 1, T. 19 N., R. 51 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

The Greisen prospect consists of an elongate zone which contains axinite, tourmaline, and sulfides in an igneous breccia at the contact between dacite of the Horn Mountains volcanic field and the Horn Mountains pluton (Bundtzen and others, 1998). The greisen zone is about 300 feet long and about 50 feet wide; it contains about 5-8 percent axinite, 15-20 percent tourmaline, and 1-2 percent sulfides. Disseminated galena was recognized in some hand specimens. The zone strikes roughly north-south. One grab sample of sulfide-rich greisen contained 6,800 parts per billion (ppb) silver, 119 parts per million (ppm) copper, 2,302 ppm lead, 401 ppm zinc, 924 ppm arsenic, 321 ppm antimony, 32 ppm tin, and 13.43 ppm mercury (Bundtzen and others, 1998) This is the best example of a greisen deposit in the Horn Mountains.
The Greisen prospect is in an area marked by anomalous stream sediment and panned concentrate sample sites (Gray and others, 1994; Theodorakos and others, 1992). Stream sediment samples from this area contained up to 26 ppb gold, 950 ppb silver, 290 ppm arsenic, 57 ppm antimony, 4.0 ppm mercury, 6.4 ppm bismuth, and 0.6 ppm tellurium. Panned concentrate samples contain up to 30 ppm gold, 5 ppm silver, 1,500 ppm bismuth, 500 ppm lead, 200 ppm antimony, 1,000 ppm tungsten, and 1,000 ppm boron. The panned concentrates also contained up to 1.0 percent scheelite.
Geologic map unit (-158.459010695633, 61.7693556769707)
Mineral deposit model Sn-polymetallic veins and greisen (Cox and Singer, 1986; model 20b).
Mineral deposit model number 20b
Age of mineralization Undated; may be related to the nearby Horn Mountain pluton which has been dated at 68-69 Ma (Bundtzen and others, 1998).
Alteration of deposit Axinite-tourmaline-sulfide greisen.

Production and reserves

Workings or exploration Surface sampling was conducted by the Alaska Division of Geological and Geophysical Surveys in 1990 (Bundtzen and others, 1998).
Indication of production None

References