Jumbo

Mine, Active?

Commodities and mineralogy

Main commodities Ag; Au; Cu; Fe; Mo; Zn
Ore minerals chalcopyrite; molybdenite
Gangue minerals diopside; garnet

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-2
Latitude 55.24147
Longitude -132.61541
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Jumbo Mine is at an elevation of about 2,000 feet, about 0.5 mile northwest of Copper Mountain, at the head of Jumbo Creek. The mine is shown by symbol but not named on the USGS 1:63,360-scale topographic map. It is about 0.6 mile northeast of the center of section 34, T. 76 S., R. 84 E. Kennedy (1953) provides detailed surface and underground maps of the area and the mine workings.

Geologic setting

Geologic description

Prospecting in the Jumbo Mine area began as early as 1879, although copper was reported in the area earlier by Russians and Natives (Wright, 1915; Kennedy, 1953; Herreid and others, 1978; Roppel, 1991). By 1905, considerable reserves were defined and two aerial tramways, one 8,250 feet long and the other 600 feet long, were constructed from Hetta Inlet to the mine. The first ore was shipped in 1907 and by 1913, the Jumbo Mine was the biggest copper producer in the Ketchikan district. Mining ceased in 1918, and aside from a few thousand tons shipped in 1923, no ore has been produced since. The extensive underground workings consist of a large open stope, 3 tunnels, several winzes and raises, and a sublevel. The total production of the mine from 1907 to 1923 was 10.2 millions pounds of copper, 7,076 ounces of gold, and 87,778 ounces of silver, from 122,937 short tons of ore.
The mine was described in numerous early reports (Brooks, 1902; Wright and Wright, 1908; Wright, 1915; Wright and Fosse, 1946). The most detailed study of the mine was by Kennedy (1953), who described the rocks in the area in great detail, worked out the mineralogy of the skarns that are related to the deposit, and mapped the surface and underground workings. The deposit has since been examined several times. The Anaconda Company examined the property in the 1950s and conducted several geophysical surveys on it and nearby deposits in the 1960s (Gonnason Exploration, 1963; Hings, 1964; Klobusicky, 1965). Hanna Mining examined the property (Hogg, 1965), and Cominco Alaska Exploration mapped and sampled the deposit in 1989 and 1990.
The rocks in Jumbo Basin consist of intensely folded marble, calcareous schist, and quartz-mica schist, unconformably overlain by a thick greenstone unit; all are part of the Wales Group of Late Proterozoic or Cambrian age (Herreid and others, 1978; Eberlein and others, 1983; Brew, 1996). The metamorphic rocks are intruded by a large Cretaceous stock that is mainly granodiorite but locally varies to gabbro. Altered andesite dikes and sills are common. The skarn forms bands in a zone up to 1,000 feet wide at the marble-granodiorite contacts.
The deposit at the Jumbo Mine is a classic copper skarn in a roof pendant of marble, skarn, and schist above a granitic intrusion (Kennedy, 1953; Herreid and others, 1978). The skarn consists mainly, about 80 percent, of garnet and diopside. The rest includes epidote, albite, orthoclase, quartz, stilbite, and talc. The skarn is almost entirely in the marble, remnants of which are commonly preserved in the skarn. The adjacent granitic rocks are largely skarn free but have been sericitized and chloritized. Chalcopyrite is disseminated in the skarn and altered dikes but the major ore bodies are several northwest-trending lenses of chalcopyrite-rich skarn and lenses of chalcopyrite in the skarn. Wright and Wright (1908) describe the ore body then being mined as nearly vertical, 30 to 40 feet thick, 120 feet long, and 140 feet deep. Fracturing is important in localizing the skarn, and chalcopyrite is localized along post-skarn fractures. The ore contains considerable molybdenite, pyrite, pyrrhotite, and hematite; sphalerite also occurs, and chalcanthite (CuSO4.5H2O) has been identified (Leavens and Thomssen, 1977). In contrast to several nearby deposits (for example, the Magnetite Cliff deposit at CR148), no magnetite is present in the Jumbo Mine skarns. The Jumbo Mine also is of considerable interest as a source of specimens of diopside and garnet.
Kennedy (1952) indicated that no ore reserves remained in the Jumbo Mine. However, he and Bufvers (1967) noted that ore-grade material was exposed in the flooded, lowest workings. Kennedy's (1952) estimates of the ore reserves in the Jumbo Basin area refer only to the Magnetite Cliff and nearby deposits (CR148), not to the Jumbo MIne. The current annual minerals report of the State of Alaska (Swainbank and others, 2002) gives the 'Jumbo' reserves as 650,000 tons of ore with 45.2 percent iron, 0.75 percent copper, 0.01 ounce of gold per ton, and 0.08 ounce of silver per ton. Those reserves almost certainly include those at the Magnetite Cliff and nearby deposits; it is not clear whether they attribute any to the Jumbo Mine (which has little if any magnetite). The State estimate may also include reserves at the Gonnason prospect (CR149).
Geologic map unit (-132.617066297714, 55.2411184040631)
Mineral deposit model Copper skarn (Cox and Singer, 1986; model 18b).
Mineral deposit model number 18b
Age of mineralization Copper skarn probably related to a deeper phase of the Cretaceous granodiorite intrusion exposed at the surface.
Alteration of deposit Development of skarn. The adjacent granitic rocks are sericitized and chloritized. Andesite dikes and sills are altered.

Production and reserves

Workings or exploration
Prospecting in the Jumbo Mine area began as early as 1879, although copper was reported in the area earlier by Russians and Natives (Wright, 1915; Kennedy, 1953; Herreid and others, 1978; Roppel, 1991). By 1905, considerable reserves were defined and two aerial tramways, one 8,250 feet long and the other 600 feet long, were constructed from Hetta Inlet to the mine. The first ore was shipped in 1907 and by 1913, the Jumbo Mine was the biggest copper producer in the Ketchikan district. Mining ceased in 1918, and aside from a few thousand tons shipped in 1923, no ore has been produced since. The extensive underground workings consist of a large open stope, 3 tunnels, several winzes and raises, and a sublevel.
The mine was described in numerous early reports (Brooks, 1902; Wright and Wright, 1908; Wright, 1915; Wright and Fosse, 1946). The most detailed study of the mine was by Kennedy (1953), who described the rocks in the area in great detail, worked out the mineralogy of the skarns that are related to the deposit, and mapped the surface and underground workings. The deposit has since been examined several times. The Anaconda Company examined the property in the 1950s and conducted several geophysical surveys on it and nearby deposits in the 1960s (Gonnason Exploration, 1963; Hings, 1964; Klobusicky, 1965). Hanna Mining examined the property (Hogg, 1965), and Cominco Alaska Exploration mapped and sampled the deposit in 1989 and 1990.
Indication of production Yes
Reserve estimates Kennedy (1952) indicated that no ore reserves remained in the Jumbo Mine. However, he and Bufvers (1967) noted that ore-grade material was exposed in the flooded, lowest workings. Kennedy's (1952) estimates of the ore reserves in the Jumbo Basin area refer only to the Magnetite Cliff and nearby deposits (CR148), not to the Jumbo MIne. The current annual minerals report of the State of Alaska (Swainbank and others, 2002)--as have their annual reports for many years--gives the 'Jumbo' reserves as 650,000 tons of ore with 45.2 percent iron, 0.75 percent copper, 0.01 ounce of gold per ton, and 0.08 ounce of silver per ton. Those reserves almost certainly include those at the Magnetite Cliff and nearby deposits; it is not clear whether they attribute any to the Jumbo Mine (which has little if any magnetite). The State estimate may also include reserves at the Gonnason prospect (CR149).
Production notes The total production of the mine from 1907 to 1923 was 10.2 millions pounds of copper, 7,076 ounces of gold, and 87,778 ounces of silver, from 122,937 short tons of ore.

Additional comments

The Jumbo Mine is on a block of patented claims. The land around it has been conveyed to the Sealaska Corporation, who hold surface and subsurface rights, or the land is under application for transfer to them.

References

MRDS Number A010119; A010136; A010160; A010183

References

Burton, W.D., 1924, Report on the Jumbo mine, Sulzer, Alaska, 6 p. (Unpublished report held by the Bureau of Land Management, Mineral Information Center, Juneau, Alaska).
Hogg, N., 1965, Eskil Anderson properties-Jumbo Basin, Prince of Wales Island, Alaska: Unpublished report to Hanna Mining Company, 8 p. (Unpublished report held by the Bureau of Land Management, Mineral Information Center, Juneau, Alaska.)
Klobusicky, T., 1965, Examination of the Jumbo Mine, southeastern Alaska: Duval Mining Company, 10 p. (Unpublished report held by the Bureau of Land Management, Mineral Information Center, Juneau, Alaska).
Leavens, P.B., and Thomssen, R.W., 1977, Famous mineral localities: Prince of Wales Island, Alaska: Mineralogical Record, v. 8, no. 1, p. 4-12.
Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p.
Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 65 p.
Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1916: U.S. Bureau of Mines Bulletin 153, 89 p.
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004