Bosart

Mine, Inactive

Commodities and mineralogy

Main commodities Ag
Other commodities Au; Cu; Pb; Sb; Zn
Ore minerals arsenopyrite; cerussite; chalcopyrite; galena; polybasite; pyrite; sphalerite; tetrahedrite
Gangue minerals quartz; siderite

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale C-2
Latitude 63.5671
Longitude -150.898
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Bosart mine (Cobb, 1980 [OFR 80-363]) is at an elevation of about 2700 feet on the west wall of the west fork of Twentytwo Gulch. It is in the SW1/4 SW1/4 of section 32, T. 15 S., R. 17 W., Fairbanks Meridian. The location is accurate within 500 feet. The mine site corresponds to number 14 of Cobb (1972 [MF 366]), 36 of Bundtzen, Smith, and Tosdal (1976), 42 of Bundtzen (1981), 116 of Hawley and Associates (1978), and 48 of Thornsberry, McKee, and Salisbury (1984).

Geologic setting

Geologic description

The country rocks at the Bosart mine are interlayered quartz-feldspar schist and micaceous quartz schist of the Precambrian Birch Creek Schist. Greenschist is also present locally and garnet amphibolite underlies a prominent ridge about 75 feet west of the mine workings (Bundtzen, 1981, pl. 3; Thornsberry, McKee, and Salisbury, 1984, v. 2, occurrence 48).
The deposit is a thin, sulfide-rich vein that strikes N50E, and dips 70-80 NW. The vein contains arsenopyrite, pyrite, chalcopyrite, galena, sphalerite, tetrahedrite, and polybasite (Wells, 1933, p. 370-371; Bundtzen, 1981). The polybasite occurs mainly in high-grade, silver-lead ore. Some of the galena may be oxidized to cerussite.
The sulfide-rich ore contains silver assaying from a few ounces to about 40 ounces per ton; some veins assayed more than 230 ounces of silver per ton. Twenty tons of hand-picked ore shipped in 1980 averaged 0.328 ounce of gold and 78.22 ounces of silver per ton; some ore contained more than 1000 ounces of silver per ton.
The Bosart vein projects towards the Florence vein (MM082), which is about 0.75 mile to the southwest.
Geologic map unit (-150.900288167503, 63.5665949428422)
Mineral deposit model Polymetallic vein (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization The deposit is assumed to be Eocene (see record MM091).
Alteration of deposit Possible oxidation of lead mineral.

Production and reserves

Workings or exploration The vein was developed by Otto Bosart before 1931(Wells, 1933). It was prospected in the 1960s and 1970s by Arley Taylor and Jim Dale. In 1980, a small quantity of ore was mined and shipped. Mill ore was left in place.
Indication of production Yes; small
Reserve estimates About 75 tons of low-to medium-grade gold-silver ore was not mined; exploration probably would develop more reserves at the property.
Production notes The mine produced at least 20 tons of high-grade ore in 1980. This ore contained as much as 6.56 ounces of gold and 1564.4 ounces of silver per ton. About 75 tons of mill-grade ore was left in the walls of the high-grade vein, and a Harz-type jig plant was on the property in 1983. Probably no mining occurred after 1983 (Thornsberry, McKee, and Salisbury, 1984, v. 2).

Additional comments

The Bosart mine is in Denal National Park and Preserve.

References

MRDS Number A011205

References

Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mt. McKinley quadrangle, Alaska: M. S. Thesis, University of Alaska, College, Alaska, 238 p.
Reporters C.C. Hawley
Last report date 1/12/2001