The veins in the district consist principally of siderite (tan-colored iron carbonate) with quartz and sulfide minerals, principally tetrahedrite (a silver-rich, copper-antimony sulfide), galena (lead sulfide), sphalerite (zinc sulfide), and chalcopyrite (copper-iron sulfide). They extend over a mile below the surface. Many veins are localized along faults and fractures in more brittle quartzite units, but the deposits also show some stratigraphic control. Research on the age and origin of the Coeur d'Alene veins has been a controversial subject over the last century. The most recent thinking is that the metals were originally deposited along with the Precambrian sediments and that veins probably formed in the Cretaceous about 65 120 million years ago (Fleck and others, 2002).
Veins range from centimeters to several meters in width, are persistent over long strike lengths, and extend to great depth. Veins show little vertical mineral zoning, although some veins, such as the Star-Morning, change along strike with the Star being zinc rich and the Morning lead silver rich. Deformation after emplacement is evident in many of the veins.
Underground vein in the Galena mine. (V.S. Gillerman photograph, 2003).
Most of the ore bearing veins occupy one of three stratigraphic horizons (Figure 12): 1) the Prichard Formation near the middle quartzite (zinc-rich deposits), 2) the Prichard Burke transition zone (lead-zinc-rich deposits), and 3) Revett St. Regis transition zone (lead-silver-copper-rich deposits (Bennett, 1984).
Figure 12. Mineralized horizons in the Coeur d'Alene district (Bennett, 1984).
The Sunshine Mine was staked in 1884 by True and Dennis Blake, brothers from Maine, who had a homestead on Big Creek. In 1931, a major strike of rich silver-bearing ore was made on the 1700 level. The "Shine" has produced some 367 million ounces of silver, probably the largest silver production of any single silver mine in the world. By comparison, the fabled Comstock lode in Nevada produced about 200 million ounces of silver from many mines. Unfortunately, the Sunshine Mining Company ran short of ore in 1999, declared bankruptcy in 2000, and closed their office and the mine. The mine is now owned by the Sterling Mining Company and is being studied for possible reopening. In 2006, Sterling Mining Company began driving a decline (the Sterling Drift Project) from the Silver Summit Mine towards the main Sunshine mine as part of a major exploration project. The $2.8 million project is expected to take 15 months to complete. By September, the drift was in some 1,100 feet and projected to go to 4,500 feet including some 1,200 feet of secondary drifts.
Historical picture of the Sunshine hoist.
Figure 14. Headframe for the Jewell shaft and mill buildings of the Sunshine Mine, date unknown. The shaft was named for the engineer in charge of sinking the shaft.
Figure 15 Underground ore in the West Chance vein of the Sunshine Mine (V.S. Gillerman photograph, 1997). Note the sheared nature of the vein.
Figure 16. Headframe for the Jewell shaft and mill buildings of the Sunshine Mine, circa 2000. Compare this photograph with Figure 14 (E.H. Bennett photograph).
Figure 17. Cross-section of the Sunshine Mine, showing the Sterling Drift and other workings (Bennett, 2006).
Underground mining is difficult work and not without risk. In May 1972, a fire that killed 91 miners by smoke inhalation and carbon monoxide poisoning occurred at the Sunshine Mine. This was one of the worst mining disasters in history (Figure 18).
Figure 18. Memorial to the miners who died in the Sunshine Mine disaster (V.S. Gillerman photograph, 2005).
The Bunker Hill Mine was discovered in 1885. In 1887 Simeon Reed, a Portland, Oregon, businessan, purchased the mine and formed the Bunker Hill Mining and Concentrating Company. In 1903, the 2-mile-long Kellogg tunnel (Figure 19) was completed, and the huge March ore body was discovered in 1904. Figure 20 shows the extent of the upper workings in 1908 or a little earlier. The company built its own smelter in 1917 and an electrolytic zinc plant (with Hecla Mining Company) in 1928.
Figure 19. Portal of the Kellogg tunnel (M.J. Weaver photograph, 2005).
Figure 20. Upper workings of the Bunker Hill Mine, circa 1908 (Ransome and Calkins, 1908).
Both plants underwent substantial changes over the years, including the addition of the 715-foot-high stack at the smelter (Figure 21) and the 610-foot-high stack at the zinc plant completed in 1978. Bunker Hill was instrumental in developing uses for zinc and contributed much to the zinc die-casting industry. In later years, sulfuric acid generated from the smelter was combined with phosphate ore from southeastern Idaho to make fertilizer. Gulf Resources and Chemical Corporation purchased the Bunker Hill Company in 1968, but closed the operation in 1981 with the loss of 2,100 jobs. When the mine and metallurgical complex closed, it was producing about 20 percent of the nation's refined lead and zinc and 25 percent of its silver. The mine was reopened in 1988, but closed again in 1991.
Figure 21. Aerial view of the Bunker Hill smelter, circa 1984 (E.H. Bennett photograph).
There are over 150 miles of underground workings (Figure 22), and it is the largest lead-zinc mine in the United States. An auction was held in 1991 and the mine was stripped. The New Bunker Hill Company purchased the mine and has been slowly refitting the underground facility for production. The mine still contains substantial reserves of zinc-rich ore (Bennett, 2006).
Map and cross-section showing the Bunker Hill Mine workings circa 1908. The mine workings became much more extensive before the mine closed (Ransome and Calkins, 1908).
The Morning mine was developed in 1889 by Charles Hussey, a Spokane banker. After the mine was sold in 1897, a new mill was built, and the No. 6 tunnel was driven from the mill site near Mullan to the mine. In 1905, the mine (Figures 23 and 24) was purchased by the Federal Mining and Smelting Company, which merged with Asarco in 1953. At the Morning mill, Federal's metallurgists wrestled with the problem of separating zinc and lead from the complex ore. Selective flotation, discovered in the 1920s, solved this problem. In 1961, Hecla leased the mine and in 1966 purchased the property.
Figure 23. Mill at the Morning mine, circa 1908 (Ransome and Calkins, 1908).
Figure 24. Plan and longitudinal vertical projection of the workings of the Morning Mine, circa 1908 (Ransome and Calkins, 1908).
The Morning mine and Star mine, both on the same orebody (Figure 25), were then operated as the Star-Morning unit. The Morning Mine on the east end of the orebody is lead/silver-rich whereas the Star Mine is zinc-rich. Fire destroyed the Morning mill in 1957. Hecla quit mining the Star-Morning in 1982. The Star-Phoenix Mining Company leased the mine, but the Star-Morning again closed in 1990. The Star-Morning has the second largest production in the district after the Bunker Hill (Bennett, 2006).
Figure 25. Projection of underground workings of the Star and Morning mines between Burke and Mullan, Idaho (Bennett and others, 1989).
The Galena Mine had been mined off and on until the Great Depression in the 1930s. In 1947, Asarco leased the mine, and a shaft sunk almost 3,000 feet found commercial silver ore. This new Galena Mine was placed in production in 1955 and was one of the largest producers in the district. This was due to Asarco's efficient operation and to more than twenty-two years of labor harmony. The mine closed in 1991 due to low metal prices, but was reopened in 1996 under a new partnership between Coeur d’Alene Mines Corp. and Asarco called Silver Valley Resources Corporation. In 1999, Coeur d’Alene Mines Corp. bought out Asarco’s interest in the partnership and took over operation of the mine.
The photographs to the right show the headframe and the large hoist needed to move men and supplies to and from the lower levels. In 2006, Coeur d’Alene Mines sold the Galena and Coeur mines and other holdings to U.S. Silver Corporation. The Galena is in full production and has developed significant new reserves for future operations. The mine employs about 180 people (Photographs by V.S. Gillerman, 2005 and Bennett, 2006).
This shows a loaded face at the Galena mine prior to being blasted (area where mine excavation is advancing) (V.S. Gillerman photograph, 2001). Large mucking machines are used to remove the rock after each blast. Sturdy timbers are needed to support the tunnels after the rock that has been blasted is removed
Mucking (removing) waste at the 2400 level (feet below land surface) in the Galena mine (V.S. Gillerman photograph, 2003). Support timbers for the Galena mine (V.S. Gillerman photograph, 2005).
Like the Sunshine and Galena mines, the Lucky Friday was a late bloomer in the district. In 1912, the Friday was sold at a sheriff’s sale for $2,000 and again in 1936 for $120 in back taxes. In 1938, John Sekulic, a garage mechanic in Mullan, purchased the mine for $15,000 and formed the Lucky Friday Mining Company. With a lot of faith in the venture and enough technical and financial help from Judge Albert Featherstone, the president of Golconda Mining Company, mining began in earnest. The company shipped its first ore in 1942. The ore got better and better as the shaft went deeper.
Hecla Mining Company started buying stock in the Lucky Friday, and in 1964 the two companies merged. In 1980, the company began sinking the $40 million "Silver Shaft" at the Lucky Friday. The shaft is now 6,000 feet below the surface and the main production shaft at the mine. The 140-foot-high headframe stands in contrast to the old hoist works visible on the hill behind the mine offices. The Lucky Friday produced over 125 million ounces of silver through 2002.
Headframe for the Silver Shaft at the Lucky Friday Mine (V.S. Gillerman photograph, 2005).
Figure 32. Miner drilling vein at the 5500 level (feet below land surface) in the Lucky Friday Mine (V.S. Gillerman photograph, 1996).
The Gold Hunter was developed by Day Mines, Inc. The ore was rich, but spotty. In 1977, Hecla decided to look below the Gold Hunter mine for the downward extension of the Hunter veins. The exploration was successful. Today ore is mined from the 5900 level of the Hunter, and the mineralization extends to 7,900 feet. The Gold Hunter (Figure 33) is now the primary source of ore mined from the Silver Shaft at the Lucky Friday mine (Bennett, 2006).
Figure 33. Diagram of the Gold Hunter and Lucky Friday workings (Bennett, 2006).
The Coeur Mine was placed in production in 1974. It was owned by Coeur d’Alene Mines Corporation and operated by Asarco until 1991. It opened briefly in 1996, but closed again because of low reserves. The Coeur (Figure 34) produced about 2.5 million ounces of silver a year (Bennett, 2006).
Figure 34. Coeur Mine circa 1991 (V.S. Gillerman photograph).
Labor unrest was a problem throughout the district in the 1890s, and martial law was declared on two occasions. In 1899 labor agitators destroyed the Bunker Hill mill with a massive explosion of dynamite (Figure 35). Attempts, often successful, to destroy property were a favorite tactic used by union organizers against companies whose management was opposed to having unions at their mines.
Figure 35. Bunker Hill mill following explosion in 1899. (Engineering and Mining Journal, v. 67, p. 648).
Originally, the mills in the district dumped mill tailings (waste material) into the Coeur d'Alene River and its tributaries (Figure 36). Periodic flooding moved the metal-rich tailings through the drainage and into Coeur d'Alene Lake.
This contaminated the Silver Valley and the lake with metals. Around 1900, large wooden tailings dams were built on Canyon Creek and near Osburn and Pinehurst (Figure 37 and 38). These dams were frequently breached by spring runoff. In 1944, Hecla Mining Company built a sink-and-float plant near Osburn to reclaim zinc and lead from 2 million tons of old mill tailings that filled the valley. The plant produced substantial amounts of metals, but it burned down in 1948.
Figure 36. Location of tailings dams and of dumps reworked for additional metals in the Coeur d'Alene district (Bennett, 2006).
Figure 37. Osburn Flats filled with tailings, circa 1900 (photograph from Shoshone County Courthouse).
Figures 37 and 38 were taken looking east from Two-Mile Creek and show how Osburn Flats looked just after 1900 and in 1993.
Figure 38. Osburn Flats, 1993. The mill tailings were removed during World War II (E.H. Bennett photograph).
In 1982, the Environmental Protection Agency declared a 21-square-mile area that included the Bunker Hill smelter and zinc plant as a Superfund site. EPA, the state of Idaho, and the mining companies have contributed substantially to remediating the damage from past mining. Over 3,000 homes in the Superfund area have had the dirt in their yards replaced to decrease the problem of fugitive lead. The zinc plant, smelter, and concentrator have been removed as well as the tall smoke stacks (Figure 39). Thousands of cubic yards of contaminated soil from Smelterville flats has been excavated and placed in a repository, and millions of trees have been planted on the hillsides in back of the smelter and zinc plant.
Figure 39. On May 26, 1996, the smoke stacks for the smelter and the zinc plant were dropped into trenches and buried (E.H. Bennett photograph).
Bennett, E.H., 1984, A hypothesis concerning the genesis of orebodies in the Coeur d'Alene mining district, Idaho : Idaho Geological Survey Technical Report TR-84-7, 39 p.
Bennett, E.H., 2006, The fabulous Coeur d'Alene district: Presentation for North Idaho Chamber of Commerce Legislative Tour, November 2006, Post Falls , Idaho , 35 p.
Bennett, E.H., P.L. Siems, and J.T. Constantopoulos, 1989, The geology and history of the Coeur d'Alene mining district, in V. E. Chamberlain, Roy M. Breckenridge, and Bill Bonnichsen, editors, Guidebook to the Geology of Northern and Western Idaho and Surrounding Area: Idaho Geological Survey Bulletin 28, p. 137-156.
Bennett, E.H., and Venkatakrishnan, 1982, A palinspastic reconstruction of the Coeur d'Alene mining district based on ore deposits and structural data: Economic Geology, v. 77, p. 1851-1866.
Doughty, P.T., and Price, R.A., 2000, Geology of the Purcell Trench rift valley and the Sandpoint Conglomerate: Eocene en echelon normal faulting and syrift sedimentation along the eastern flank of the Priest River metamorphic complex, northern Idaho : Geological Society of America Bulletin, v. 112, no. 9, p. 1356-1374.
Doughty, P.T., Price, R.A., and Parrish, R.R., 1997, Geology and U-Pb geochronology of Archean basement and Proterozoic cover in the Priest River complex, northwestern Unite States , and their implications for Cordilleran structure and Precambrian continent reconstructions: Canadian Journal of Earth Science, v. 35, p. 39-54.
Fleck, R.J., R.E. Criss, G.F. Eaton, R.W. Cleland, C.S. Wavra, and W.D. Bond, 2002, Age and origin of base- and precious-metal veins of the Coeur d'Alene mining district, Idaho : Economic Geology, v.97, no.1, p. 23-42 .
Hobbs , S.W., A.B. Griggs, R.E. Wallace, and A.B. Campbell, 1965, Geology of the Coeur d'Alene district, Shoshone County , Idaho : U.S. Geological Survey Professional Paper 478, 139 p., scale 1:24,000.
Orr, W.N., and Ore , E.L., 2002, Geology of the Pacific Northwest : 2 nd Edition, McGraw-Hill Higher Education, 337.
Ransome, F. L., and F. C. Calkins, 1908, The geology and ore deposits of the Coeur d'Alene district, Idaho : U.S. Geological Survey Professional Paper 62, 203 p.
White, B.G., 2000, Coeur d'Alene mining district: product of preconcentrated source deposits and tectonism within the Lewis and Clark line, in Sheila Roberts and Don Winston, eds., Geologic field trips, western Montana and adjacent areas: Rocky Mountain Section of the Geological Society of America, University of Montana , p. 95-101.
Winston, Don, 2000, Belt Supergroup stratigraphy, sedimentology, and structure in the vicinity of the Coeur d'Alene mining district, in Sheila Roberts and Don Winston, eds., Geologic field trips, western Montana and adjacent areas: Rocky Mountain Section of the Geological Society of America, University of Montana, p. 85-94.
Wyld, S.J., Umhoefer, P.J., and Wright, J.E., 2006, Reconstructing northern Cordilleran terranes along known Cretaceous and Cenozoic strike-slip faults: Implications for the Baja British Columbia hypothesis and other models, in Haggart, J.W., Enkin, R.J., and Monger, J.W.H., eds., Paleogeography of the North American Cordillera: Evidence for and against large-scale displacements: Geological Association of Canada, Special Paper 46, p. 277-298.
Continue to Module 8 - Challis Volcanics