Unnamed (near Geyser Creek)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Au
Other commodities As; Hg
Ore minerals gold; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale UK
Quadrangle map, 1:63,360-scale A-2
Latitude 53.2
Longitude -168.5
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is located near Geyser Creek on Umnak Island, approximately 3 miles southeast of Geyser Bight. Simpson's (1986) location of this site is vague and it could correspond to locations G or L which are mapped as clusters of hot-springs (Nye and others, 1992). The location is probably accurate to within 2 miles.

Geologic setting

Geologic description

Geothermal activity at this site is indicated by a 800 x 2000 foot color anomaly (Simpson, 1986). The rocks here consist of propylitized andesitic flows, tuffs, and volcaniclastics of Pleistocene age. The altered rocks exhibit local zones of intense argillization and weak silicification. The clay zones contain up to 2 percent disseminated pyrite.
Nye and others (1992) report dioritic and monzonitic plutons at low elevations on the east and west walls of the lower half of Geyser Creek valley, and they speculate that the plutons may host the geothermal reservoir system.
Analyses of 20 rock samples indicated values up to 150 ppm arsenic, 0.58 ppm gold, 1.25 ppm mercury, and 0.2 ppm silver (Simpson, 1985, table 11, pg. 38). In general, the only rocks which contain gold are those which exhibit pyritization and moderate silicification. There does not appear to be any lateral or vertical zonation of the metals.
Geologic map unit (-168.502008930307, 53.1990663276063)
Mineral deposit model Hot-spring Au-Ag (Cox and Singer, 1986; model 25a)
Mineral deposit model number 25a
Age of mineralization Quaternary.
Alteration of deposit The volcanic rocks exhibit regional propylitic alteration and local intense argillic alteration and weak silicification. The clay zones contain up to 2 percent pyrite and thin, discontinuous quartz veins.

Production and reserves

Workings or exploration Twenty samples collected by Kennecott were found to contain 8 to 150 ppm arsenic, 0.005 to 0.58 ppm gold, 0.005 to 1.25 ppm mercury, and 0.2 to 0.6 ppm silver (Simpson, 1986).
Indication of production None

Additional comments

This site is on land selected by the Aleut Native Corporation.


MRDS Number 10308466


Reporters S.H. Pilcher (Anchorage)
Last report date 1/27/2000