Jumbo

Mine, Undetermined

Alternative names

Gold Reef No. 1
Minnesota
Duluth

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale SI
Quadrangle map, 1:63,360-scale C-7
Latitude 57.6539
Longitude -136.1053
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Jumbo Mine is a few feet above sea level on the west shore of Klag Bay, about a mile from the ruins of the town of Chichagof. The mine is 0.4 mile northeast of the center of sec. 4, T. 49 S., R. 58 E. It is location P-70 of Bittenbender and others (1999), location 32 of Cobb (1972, 1978), and MAS no. 0021140049 (U.S. Bureau of Land Management, 2002). The location is accurate.
Bittenbender and others (fig. 6) show shafts 0.4 mile and 0.6 mile northwest of this site that are probably on the Gold Reef or Minnesota claims described by Reed and Coats (1941). Reed and Coats list the Jumbo, Duluth, Minnesota, and Gold Reef No. 1 claims under the heading 'Smith prospects.'

Geologic setting

Geologic description

Johnson and Karl (1985) map the rocks in the area of these properties as Cretaceous graywacke and argillite interbedded with sparse, lenticular beds of basalt. The rocks are cut by numerous high-angle, mainly northwest-striking faults. They include the extension of the fault at the, Chichagof Mine (SI093) that controls the mineralization there and whose traces is about a mile northeast of this mine.
Reed and Coats (1941) list the Jumbo, Duluth, Minnesota, and Gold Reef No. 1 claims under the heading 'Smith prospects.' All of the claims were staked between 1909-1912. Various early workings on the claims explored northwest-striking, steeply-dipping, fault-controlled, mineralized quartz veins up to 2 feet thick in locally slaty graywacke. The veins contain galena, sphalerite, pyrite, and free gold, and some of the district's best specimens of free gold came from the Jumbo deposit.
Bittenbender and others (1999), citing Overbeck (1919), Reed and Coats (1941), and Still and Weir (1981), report that the Jumbo deposit was discovered in 1909, when 1,450 ounces of gold were mined from a high-grade pocket in the intertidal zone. Some of the richest ore in the district was from this mine. From 1909 to 1931, workings included a 400-foot shaft, 1,580 feet of drift off the shaft, and numerous pits and trenches. A U.S. Bureau of Mines examination in 1978 and 1978 (Still and Weir, 1981) revealed quartz along a fault zone that extends for 3,000 feet in graywacke. Workings visible at that time included 3 flooded shafts and a 48-foot drift. They collected 18 surface samples along the vein that contained up to 0.15 ounce of gold per ton. Incomplete company maps and records of underground mining prevented an estimate of resources.
Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler and others, 1995; Goldfarb, 1997; Goldfarb and others, 1997). ARDF record SI087 provides an overview of the geology of auriferous quartz veins in the Chichagof Mining District.
Geologic map unit (-136.107124166367, 57.6535284955153)
Mineral deposit model Polymetallic vein (Cox and Singer, 1986; model 22c).
Mineral deposit model number 22c
Age of mineralization Isotopic studies indicate that the gold-quartz veins in coastal southern and southeastern Alaska are Eocene, about 50 Ma in age (Haeussler and others, 1995; Goldfarb, 1997; Goldfarb and others, 1997).

Production and reserves

Workings or exploration From 1909 to 1931, workings included a 400-foot shaft, 1,580 feet of drift off the shaft, and numerous pits and trenches. Workings visible during a US Bureau of Mines examination in 1978 and 1978 were 3 flooded shafts and a 48-foot drift.
Indication of production Yes; medium
Reserve estimates The US Bureau of Mines sampled extensively in 1978 and 1979, but incomplete company maps and records of underground mining prevented an estimate of resources.
Production notes The Jumbo Mine produced 1,450 ounces of gold in 1909 from a high-grade pocket in the intertidal zone. Significant amounts of gold probably were recovered in later years, but there are no other published records of production.

Additional comments

The area is in West Chichagof-Yakobi Wilderness.

References

MRDS Number A013272; A013273

References

Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p.
Goldfarb, R J., 1997, Metallogenic evolution of Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 4-34.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Haeussler, P J., Bradley, D., Goldfarb, R., Snee, L., and Taylor, C., 1995, Link between ridge subduction and gold mineralization in southern Alaska: Geology, v. 23, no. 11, p. 995-998.
U.S. Bureau of Land Management, 2002, Alaska mineral locations database report (Sitka quadrangle), July 2, 2002, 205 p. [http://imcg.wr.usgs.gov/dem.html]
Reporters H.C. Berg (U.S. Geological Survey)
Last report date 10/16/2004