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Michigan Lode; Michigan Lead Prospect, Goodpaster District, Southeast Fairbanks Borough, Alaska, USA

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Location: The Michigan Lode is situated on a ridge of Black Mountain separating the headwaters of Antimony Creek, a tributary of Tibbs Creek (BD040), and Summitt Creek, a tributary of Boulder Creek (BD004). The prospect is located in the SW1/4SW1/4 section 28, T. 6 S., R. 18 E., of the Fairbanks Meridian, approximately 54 miles east-northeast of Delta Junction, Alaska. A winter trail from the South Fork of the Goodpaster River provides access up Divide Creek. There are numerous surface workings at and surrounding the site. The site is incorrectly labeled on current U.S.G.S. maps as a mine. It was not identified as a separate location by Cobb (1972) or by Cobb and Eberlein (1980). Approximately one mile north of the Michigan Lode, U.S.G.S. maps note some mining activity on the ridge between Wolverine Creek and Antimony Creek in the SW1/4SE1/4 section 20, T. 6 S., R. 18 E., of the Fairbanks Meridian.
Geology: The topography of the area is characterized by rounded hills and flat-topped ridges (Thomas, 1970). The most prominent ridge is Black Mountain, which trends about 12 miles in a northerly direction and is underlain by Cretaceous granodiorite (Weber and others, 1978). Several creeks flow westward off Black Mountain in steep, parallel, V-shaped valleys to form the headwaters of Tibbs Creek. A combination of augen gneiss, gneissic schist, and schist are to the west of Black Mountain. There is intense shearing and faulting in the contact between the metamorphic and intrusive rocks. This shearing is observed in the underground workings and at the surface as pronounced saddle-like depressions across the spurs separating the westward-flowing tributaries of Tibbs Creek. This shear zone trends roughly N15E and dips 65 degrees NW. The lode deposits in the area are gold-bearing quartz veins in the shear zone. Most of the veins are in the shear zone, although some are in the intrusive rocks. The quartz veins contain gold and a variable assemblage of sulfides, including arsenopyrite, covellite, digenite, jamesonite, pyrite, and stibnite. Typically, gold content decreases as sulfides increase. Veins are commonly 2 to 3 feet in width, with some as wide as 8 feet (Thomas, 1970). When gold is present, it is usually extremely fine grained. However, several veins such as the Blue Lead mine (BD003) and Grizzly Bear mine (BD018) contain relatively coarse gold, which is easily visible in hand specimen. Thomas (1970) describes the Michigan Lode as a surface vein. Assays from the site show 0.10 ounce/ton Au from vein quartz with a blue hue, and 0.42 ounce/ton Au and 0.08 ounce/ton Ag from some Fe-stained quartz (Thomas, 1970). The mining activity noted on U.S.G.S. maps on the ridge between Wolverine Creek and Antimony Creek is described by Thomas (1970) as trenches. An assay of a sample containing cryptocrystalline quartz with a blue cast showed 8.76 ounces/ton Au and 3.26 ounces/ton Ag (Thomas, 1970). The Goodpaster region was first explored for placer gold in 1915. In the early 1930's, gold-bearing quartz veins were discovered in the upper Tibbs Creek area. By the winter of 1936, the first underground workings were being installed. The original base camp was on Summit Creek. A 450 foot tunnel was driven following a small vein, termed the Blue Lead Extension. After disappointing results, the work was stopped. In the summer of 1936, five men drove a 300-foot tunnel at the outcrop of the Blue Lead vein (Reed, 1937). During the winter of 1937, a 300-foot tunnel was driven at the Grizzly Bear mine (BD018) and a 50-ton mill was constructed. In the summer of 1938, the mill was moved to the Blue Lead mine and operated for a year and a half until the fall of 1939 (Joesting, 1938). There was been limited exploration reported in the 1970's. The mill was still on site and the mine shaft opening were accessible in 1970, but blocked by ice (Thomas, 1970). It is reported that 350 tons of ore was produced from the Grizzly Bear mine and processed at the mill. This is compared with 150 tons from the Blue Lead mine (Reed, 1937). No ore was mined from the Michigan Lode (Thomas, 1970).
Workings: The Goodpaster region was first explored for placer gold in 1915. In the early 1930's, gold-bearing quartz veins were discovered in the nearby upper Tibbs Creek area. By the winter of 1936, the first underground workings were being installed. The original base camp was on Summit Creek. A 450-foot tunnel was driven following a small vein, termed the Blue Lead Extension. After disappointing results, the work was stopped. In the summer of 1936, five men drove a 300-foot tunnel at the outcrop of the Blue Lead vein. (Reed, 1937). During the winter of 1937, a 300-foot tunnel was driven at the Grizzly Bear Mine along with the construction of a 50-ton amalgamation recovery mill. In the summer of 1938, the mill was moved to the Blue Lead Mine and operated for 1.5 years until the fall of 1939 (Joesting, 1938). There has been limited exploration reported in the 1970's. The mill is still on site and the mine shaft opening is accessible, but blocked by ice (Thomas, 1970). It is unknown if any development took place at the Michigan Lead Mine.
Age: Postdates Cretaceous granodiorite intrusion
Production: It is reported that 350 tons of ore was produced from the nearby Grizzly Bear Mine and 150 tons from the Blue Lead Mine (Reed, 1937). No ore was mined from the Michigan Lode (Thomas, 1970).

Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Sb
Development Status: Yes; small
Deposit Model: Shear-hosted magmatic-hydrothermal vein

Mineral List



8 entries listed. 8 valid minerals.

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References

Cobb, E.H., 1972, Metallic mineral resources map of the Big Delta quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-388, 1 sheet, scale 1:250,000. Cobb, E.H., and Eberlein, G.D., 1980, Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the Big Delta and Tanacross quadrangles, Alaska: U.S. Geological Survey Open-File Report 80-1086, 77 p. Eberlein, G.D., Chapman, R.M., Foster, H.L., and Gassaway, J.S., 1977, Map and table describing known metalliferous and selected nonmetalliferous mineral deposits in central Alaska: U.S. Geological Survey Open-File Report 77-168-D, 132 p., 1 sheet, scale 1:1,000,000. Foster, H.L., Albert, N.R.D., Griscom, Andrew, Hessin, T.D., Menzie, W.D., Turner, D.L, and Wilson, F.H., 1979, The Alaskan Mineral Resource Assessment Program; Background information to accompany folio of geologic and mineral resource maps of the Big Delta quadrangle, Alaska: U.S. Geological Survey Circular 783, 19 p. Joesting, H.R., 1938, Mining and prospecting in the Goodpaster region: Alaska Territorial Department of Mines Miscellaneous Report 90-02, 2 p. Menzie, W.D., and Foster, H.L., 1979, Metalliferous and selected nonmetalliferous mineral resource potential in the Big Delta quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-529-D, 61 p., 1 sheet, scale 1:250,000. Reed, I.M., 1937, Brief report on Goodpaster quartz lode mining at the head of Johnson and Boulder Creeks: Alaska Territorial Department of Mines, 1 p. Saunders, R.H., 1967, Mineral occurences in the Yukon-Tanana region, Alaska: Alaska Division of Mines and Minerals Special Report 2, 58 p., 2 sheets, scale 1:1,000,000. Smith, P.S., 1938, Mineral industry of Alaska in 1936: U.S. Geological Survey Bulletin 897-A, p. 1-107. Smith, P.S., 1939, Mineral industry of Alaska in 1938: U.S. Geological Survey Bulletin 917-A, p. 1-113. Thomas, B.I., 1970, Reconnaissance of the gold-bearing quartz veins in the Tibbs Creek area, Goodpaster River, Big Delta quadrangle, central Alaska: U.S. Bureau of Mines Open-File Report 14-70, 12 p., 3 sheets. Weber, F.R., Foster, H.L., Keith, T.E.C., Dusel-Bacon, Cynthia, 1978, Preliminary geologic map of the Big Delta quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-529-A, 1 sheet, scale 1:250,000.

 
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