Jumbo Mine, Mount Jumbo, Prince of Wales Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Jumbo Mine	Mine
Mount Jumbo	Mountain
Prince of Wales Island	Island
Ketchikan Mining District	Mining District
Prince of Wales-Hyder Census Area	Census Area
Alaska	State
USA	Country

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.
Location: 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.
Geology: 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 1950's and conducted several geophysical surveys on it and nearby deposits in the 1960's (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)--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).
Workings: 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 1950's and conducted several geophysical surveys on it and nearby deposits in the 1960's (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.
Age: Copper skarn probably related to a deeper phase of the Cretaceous granodiorite intrusion exposed at the surface.
Alteration: Development of skarn. The adjacent granitic rocks are sericitized and chloritized. Andesite dikes and sills are altered.
Production: 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.
Reserves: 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).

Commodities (Major) - Ag, Au, Cu, Fe, Mo, Zn
Development Status: Yes
Deposit Model: Copper skarn (Cox and Singer, 1986; model 18b).

Other Databases

Link to USGS - Alaska:	CR150

Other Regions, Features and Areas containing this locality

References