Sitka

Mine, Active

Alternative names

Sitka Gold Mine
Unga

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Cu; Pb; Zn
Ore minerals chalcopyrite; galena; gold; pyrite; sphalerite
Gangue minerals adularia; calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale PM
Quadrangle map, 1:63,360-scale A-2
Latitude 55.194
Longitude -160.554
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is located on the southeast part of Unga Island approximately 2,600 feet northwest of the head of Delarof Harbor and 1,500 feet northeast of the Apollo mine (Berg and Cobb, 1967, locality 7; Cobb, 1972, locality 5; MacKevett and Holloway, 1977, locality 5; Nokleberg and others, 1987, locality AP4; Wilson and others, 1988, locality 4). The mine is near the north edge of section 5, T. 58 S., R. 74 W. of the Seward Meridian. The location is based on aerial photographs showing where the entrance to the adit is and is accurate to 100 feet.

Geologic setting

Geologic description

The Sitka deposit is a 5- to 10-foot-wide zone of auriferous quartz-sulfide veins in an east-west-striking shear that cuts rocks mapped as andesite of the Eocene to Oligocene Popof volcanic rocks (Wilson and others, 1995). The shear zone dips 65 to 80 degrees to the south. The Sitka gold vein system is part of the northeast mineralized Apollo-Sitka trend which extends over 5,000 feet across Unga Island. Anomalous gold and silver values in rock, soil, and talus samples correlate to zones of pervasive silicification and quartz-adularia-carbonate veins within an envelope of intense argillic alteration (Redstar Gold Corp., 2014b).
Mineralization is found in stockwork quartz veins containing pyrite and as much as 5 percent chalcopyrite and galena, along with lesser amounts of sphalerite. They are vuggy and show evidence of open-space filling, resulting in inward-facing euhedral quartz crystals. The sulfides occur mostly at the base of the quartz crystals. The stockwork quartz veins are within volcanic rocks and appears to be extensive though the width of mineralization is not known. Trenches expose some of the stockwork quartz veining indicating a minimum width of 50 meters (Redstar Gold Corp., 2012).
Geologic map unit (-160.556034414322, 55.1931708191785)
Mineral deposit model Sado epithermal gold veins (Cox and Singer, 1986; model 25d).
Mineral deposit model number 25d
Age of mineralization Eocene or younger, based on age of host rocks (Wilson and others, 1995).
Alteration of deposit Anomalous gold and silver values in rock, soil, and talus samples correlate to zones of pervasive silicification and quartz-adularia-carbonate veins within an envelope of intense argillic alteration (Redstar Gold Corp., 2014b).

Production and reserves

Workings or exploration
The Sitka mine was operated in conjunction with the Apollo mine (PM079) from 1900 until about 1915. Workings at that time consisted in part of a 400-foot shaft, a 360-foot adit, stopes as much as 150 feet long and 15 feet wide on the 55-foot level, and numerous crosscuts (Wilson and others, 1988). Production to that time was estimated at 15,000 tons of unknown grade (Brown, 1947). The gold, where mined, was free-milling (Atwood, 1911). In 1983 Alaska Apollo Mines cut six trenches and drilled three core holes for a total of 1,571 feet. The remaining resource is said to be 140,000 tons (Wilson and others, 1996).
In 2011 Redstar Gold Corp. (Redstar) collected several rock samples from the Sitka mine shaft across the gold-silver vein that contained 13.2 grams per tonne (g/t) gold and 398 g/t silver over 2 meters. Vein material sampled from the mine dump returned 15.2 g/t gold and 316 g/t silver (Redstar Gold Corp., 2012).
Redstar remapped and collected continuous chip and select rock samples in 2014 from 235 meters of the historic trenches at Sitka to better understand the characteristics of historic mining activities (Redstar Gold Corp., 2014a). Continuous rock chip trench sampling of intense quartz-adularia-carbonate stockwork veins within a stope at Sitka contained up to 30.5 g/t gold and 128 g/t silver. Sampling along the Apollo-Sitka trend showed a continuous gold and silver soil anomaly of over 100 parts per billion (ppb) gold and over 1.3 g/t silver, extending 1,300 meters to the southwest of Apollo (PM079) (Redstar Gold Corp., 2014b).
Redstar Gold Corp. conducted two phases of exploration in 2016 on their Unga project, which includes the Shumagin (PM064), Apollo (PM079; PM084), Centennial, Orange Mountain (PM067), Zachary Bay (PM054), Amethyst (PM092), and Aquila (PM086) epithermal gold-silver prospects. The Shumagin trend parallels the historically mined Apollo–Sitka vein system (PM079; PM084; PM076), which between 1886 and 1922 produced approximately 150,000 ounces of gold at a grade of approximately 0.292 ounce of gold per ton (Athey and Werdon, 2017).
In June 2016, Redstar Gold Corp.’s Phase I surface program included classifying alteration assemblages and conducting other geologic work to identify drill targets. From October through November, Phase II’s drilling program tested the down-dip and along-strike expansion potential of high-grade vein/breccia mineralization within the Shumigan Gold Zone (PM064). A total of 1,505 meters were drilled in 7 holes spaced over ~750 meters of strike length. All drill holes intersected the target structure, which includes multi-generational phreatomagmatic breccias, hydrothermal breccias, and late breccias and veins with colloform-crustiform- to cockade-textured quartz-adularia-carbonate (± rhodochrosite, ± green clay). Select intervals from drill holes 16SH019 and 16SH020 include 0.9 meter at 14.95 grams of gold per tonne and 1.15 meters at 11.3 grams of gold per tonne; release of full assay results is planned for late January 2017 (Athey and Werdon, 2017).
Indication of production Yes; small
Reserve estimates The resource is estimated 140,000 tons (reported in Alaska Construction and Oil, 1984). The grade is not available.
Production notes The estimated production is about 15,000 tons of unknown grade (Brown, 1947).

Additional comments

The Sitka mine is located on patented mining claims owned by Redstar Gold Corp. (Redstar Gold Corp., 2015).

References

MRDS Number A013200

References

Alaska Construction and Oil, 1984, Alaska mining? Gold Production could redouble: Alaska Construction and Oil, v. 25, no. 3, p. 31.
Reporters S.H. Pilcher; N.V. King (Alaska Earth Sciences); M.B. Werdon (DGGS)
Last report date 8/26/2017