Unnamed (in saddle between Post River and South Fork)

Occurrence, Inactive

Commodities and mineralogy

Main commodities As
Other commodities Au; Sb
Ore minerals arsenopyrite
Gangue minerals carbonate; quartz

Geographic location

Quadrangle map, 1:250,000-scale MG
Quadrangle map, 1:63,360-scale A-1
Latitude 62.014
Longitude -153.442
Nearby scientific data Find additional scientific data near this location
Location and accuracy This unnamed occurrence is located in a saddle between tributaries of the Post River and South Fork of the Kuskokwim River; it is at an elevation of 5,150 feet (1,570 m) in the center of sec. 11, T. 22 N., R. 23 W., of the Seward Meridian. The reporter visited the site in 1988; at station no. 88BT164.

Geologic setting

Geologic description

This unnamed occurrence is a low-sulfide, quartz-carbonate vein or veins intruding a border phase of the 37.9 Ma, Hartman Pluton (Solie and others, 1991; Bundtzen, Harris, and Gilbert, 1997). The border phase consists of very fine-grained biotite-rich granodiorite and monzonite. The border phase is in contact with a massive hornfels aureole that is approximately 125 meters wide.
A one meter wide, low sulfide, quartz carbonate vein swarm strikes N70W for about 115 meters through the saddle. The veins cuts the intrusive border phase, but apparently die out in the hornfels aureole. Disseminated arsenopyrite and pyrite grains occur near vein margins. One grab sample of the mineralized vein contained 6,500 ppm arsenic, 71 ppb gold, and 250 ppm antimony.
Geologic map unit (-153.444231014052, 62.0133840287372)
Mineral deposit model Polymetallic vein (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Alteration of deposit Secondary biotite (potassic) in the border phase.

Production and reserves

Workings or exploration The reporter sampled the occurrence during a geologic mapping program for the Alaska Division of Geological and Geophysical Surveys in 1988 (Bundtzen, Harris, and Gilbert, 1997). One grab sample of the mineralized vein contained 6,500 ppm arsenic, 71 ppm gold, and 250 ppm antimony.
Indication of production None
Reserve estimates None.