Main commodities | Ag |
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Other commodities | Au; Cu; Pb; Sb; Zn |
Ore minerals | arsenopyrite; cerussite; chalcopyrite; galena; polybasite; pyrite; sphalerite; tetrahedrite |
Gangue minerals | quartz; siderite |
Quadrangle map, 1:250,000-scale | DN |
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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 descriptionThe 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 N 50 E, 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 (DN082), which is about 0.75 mile to the southwest. | |
Geologic map unit | (, ) |
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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 DN091). |
Alteration of deposit | Possible oxidation of lead mineral. |
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. |
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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 commentsThe Bosart mine is in Denal National Park and Preserve. |
MRDS Number | A011205 |
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ReferencesBundtzen, 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.
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Reporters | C.C. Hawley |
Last report date | 1/12/2001 |