Location: The Berners Tunnel prospect is at an elevation of about 150 feet in a short, unnamed north tributary to Johnson Creek. It is 3.5 miles south of Lions Head Mountain and 2 miles north-northwest of Berners Bay, in the SE1/4 section 14, T. 35 S., R. 62 E. of the Copper River Meridian. The location is accurate.
Geology: The Berners Tunnel was begun in 1914 to drain water from the Jualin Mine (Redman and others, 1989). The tunnel, which trends northwesterly, was never completed. During construction, workers collected ten-foot rock-chip samples along its 5,000-foot length. Two intervals contained elevated gold values. Between station 1912 and 2042 from the portal, a 130-foot zone averaged 0.12 ounce of gold per ton; between station 2112 and 2212, a 100-foot zone averaged 0.087 ounce of gold per ton. The first 400 feet of the tunnel was in glacial till and colluvium and the portal has long since collapsed. In 1989, Placer Dome U.S. drilled 3 core holes along the trace of the Berners Tunnel. The drill holes cut numerous anomalous zones along a major NW-trending shear zone. The richest intercept averaged 0.028 ounce of gold per ton. The drill core consists of moderately to strongly sheared diorite with widespread potassic and sericitic alteration. The potassic alteration suite includes epidote, chlorite, and pyrite. Locally, the sheared diorite is highly silicified giving it a bleached appearance. This silicified diorite contains relatively abundant pyrite and chalcopyrite, and quartz-pyrite veinlets (Barnett and others, 1989). The Berners Tunnel is in the Jualin mine area (see JU044). It is in the Berners Bay district at the north end of the Juneau Gold Belt. The district is characterized by a series of structurally-controlled, mesothermal, gold-bearing quartz veins. Most of the veins are in Early Cretaceous (105 Ma) Jualin Diorite, which intrudes Mesozoic (Upper Triassic) metabasalt. Both extensional and shear veins are present that generally strike north to northwest and dip east. Discrete vein systems are defined by one or more through-going quartz veins, many of which are in shear zones (Miller and others, 1995). Hydrothermal muscovite from veins in the Jualin mine are 53.2 Ma to 55.5 Ma (Miller and others, 1994). This coincides with the 55 Ma age of the other mesothermal gold veins in the Juneau Gold Belt (Goldfarb and others, 1997).
Workings: The site consists of a 5,000-foot tunnel which is caved at the portal. Placer Dome U.S. drilled 3 core holes along the trace of the tunnel in 1989.
Age: Hydrothermal muscovite from veins in the Jualin mine are 53.2 Ma to 55.5 Ma (Miller and others, 1994). This coincides with the 55 Ma age of the other mesothermal gold veins in the Juneau Gold Belt (Goldfarb and others, 1997).
Alteration: The drill core consists of moderately to strongly sheared diorite showing widespread potassic and sericitic alteration. The potassic alteration suite includes epidote, chlorite, and pyrite. Locally, the sheared diorite is highly silicified giving it a bleached appearance.

Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Zn
Development Status: None
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

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Mineral List

6 valid minerals.