September 4, 2008
Minerals of the Wolf Tone Mine: Leadville Mining District, Lake County, Colorado
By Rosemeyer, Tom
The Leadville mining district, whose history, geology, and mineralogy have been described in numerous publications, is one of the most famous silver mining camps in the United States. For an in- depth study of the ore deposits and mineralogy of the district, the reader is referred to Emmons, Irving, and Loughlin (1927), Loughlin (1918, 1926), and Shannon and Shannon (1985). The fortunes of mining made several individuals millionaires, mostly from the profits of the rich silver mines that produced more than 250 million ounces of silver during the life of the Leadville camp. Possibly the most famous Leadville millionaire and "silver king" was Horace A. W. Tabor, who, at the height of his career, made scandalous headlines in Colorado newspapers by divorcing his straight-laced wife to marry a beautiful doll-faced young girl named Lizzie "Baby" McCourt Doe. The thriving mining camp also attracted such characters as Doc Holliday, of notorious Wild West fame, who dealt faro at the saloons lining the main street of Leadville. Interesting accounts of Leadville history and social life can be found in Blair (1980) and Voynick (1992). Life in the once-booming mining camp had tamed down considerably by the start of the twentieth century; many of the rich lead carbonate/silver mines in the district were on their last legs, and production was down. With the discovery of oxidized zinc ores in the mines on Carbonate Hill in 1909-10, new life was breathed into the economy of Leadville. This article focuses on a 2,000-ton stockpile of oxidized zinc ore that was mined in the Wolftone mine about 1918-20 but was never shipped to the smelter because of falling zinc prices following the post-World War I Great Depression.History of the Wolftone Mine
Carbonate Hill is located about 0.5 mile east of Leadville between California and Stray Horse gulches. It was named for the rich lead carbonate/silver ores that were developed by a number of mines. The Wolftone claim was staked on the northwest slope of the hill in 1876 by Samuel Morgan and Aden Alexander, and it was named after Theobald Wolfe Tone, one of the fathers of Irish nationalism (Shannon and Shannon 1985). Initial development of the Wolftone mine was by five vertical shafts that ranged from 30 to 75 feet in depth and extracted ore that ran as high as $250 per ton in lead and silver values.
In the mid-1880s the A. M. W. Company was formed by the consolidation of the Adams, Maid of Irwin, and Wolftone properties. The president and general manager of the company was Samuel D. Nicholson, a prominent Leadville mining man who eventually represented Colorado as a U.S. senator. A main production shaft for the mine was sunk on the Monte Christo claim, adjacent to the Wolftone claim, to a depth of 1,120 feet. By 1892 the Wolftone mine was a significant producer of ore from the consolidated workings. The Silver Panic of 1893 curtailed operations at many of the less profitable mines, and by the early years of the twentieth century many of the rich lead/silver orebodies in Carbonate Hill were near exhaustion, with mining reduced to a small scale. In 1904 the Western Mining Company was organized by a consolidation of the A. M. W. Company and other properties on Carbonate Hill. Simon Guggenheim was president, and Samuel D. Nicholson was appointed general manager.
Oxidized zinc ores were first discovered in the Leadville district at the Robert E. Lee mine in 1909 by W. E. Jones, who had leased the property (Loughlin 1918). The large body of replacement ore consisted of carbonates and silicates of zinc (mainly smithsonite and hemimorphite) but aroused little interest because of the low-grade character of the ore. In 1910 a second discovery of highgrade "calamine" ore was made in the Hayden shaft of the May Queen mine. At the time there was an increasing demand for zinc, and this was the first oxidized ore to be shipped to a refinery.
In the latter part of 1910, Nicholson reexamined the abandoned workings of the Wolftone mine and adjacent properties and made the most important discovery of oxidized zinc ore in the district (Holmes and Kennedy 1983). The new high-grade orebody eclipsed prior discoveries and turned out to be the district's largest deposit. Nicholson decided to celebrate the discovery as well as the rebirth of the stagnated Leadville mining industry with a huge underground banquet held in one of the abandoned stopes in the Wolftone mine. The event was held on 25 January 1911, and the day was declared a legal holiday by the mayor of Leadville. About 250 Colorado dignitaries and Leadville residents attended the gala affair deep in the bowels of the mine. The "banquet stope" was decorated with American flags and bunting, and a seven-piece orchestra played for the enjoyment of the guests. The event was topped off by an announcement of a new mineral discovery. Nicholson had sent an unidentified zinc-bearing mineral to the Colorado School of Mines for identification, and it was determined to be a new species. The new mineral was named nicholsonite in his honor; unfortunately, it was later discredited when found to be a zinc-rich variety of aragonite.
During the years of the Great War (World War I), the demand for zinc increased, and the mines of Carbonate Hill boomed. This trend continued until the signing of the armistice in 1918, which ended the hostilities in Europe and also cut the demand for zinc. The Depression followed the war, and although the mines struggled to operate, one by one they shut down. The Wolftone suspended operation in 1920 with a stockpile of approximately 2,000 tons of oxidized zinc ore that was never shipped to the smelter. Hard times followed for the mining industry and the residents of Leadville. The Leadville Deep Mines Company was formed in 1922 to dewater mines at the northern end of Stray Horse Gulch, which included the Wolftone, Adams, and R. A. M. In May 1923, large steam-driven pumps began pumping the mines, and the Wolftone and other mines operated from 1925 to 1931 (Blair 1980). By 1931 the orebodies were exhausted, and the price of zinc had fallen so low that it did not justify further exploration. The Wolftone mine suspended operations in 1931, never to reopen.
Geology of Carbonate Hill
The host rock for the orebodies in Carbonate Hill is the Leadville Formation of Mississippian age. Throughout central Colorado, the original calcium carbonate limestones of the Leadville Formation were converted to dolomite during a complicated series of alteration events. Later uplift exposed the formation to a long period of erosion. A karst topography developed that included enlarged joints, solution breccias, sinkholes, and caves. About 39.6 million years ago, igneous intrusions generated ore-forming solutions that traveled through the permeable dolomitized limestone depositing galena, sphalerite, pyrite, and chalcopyrite (Raines 2006).
A later period of prolonged erosion and weathering of the uplifted Leadville Limestone exposed the upper portions of the orebodies and produced enriched supergene deposits that contained the bonanza silver ores. The high-grade ores consisted of chlorargyrite, silver, cerussite, and anglesite, all of which were mined in the silver boom of the 1870s and 1880s.
Oxidation of sphalerite also took place, and the zinc-bearing solutions were carried away and replaced the limestone (Loughlin 1918). Reaction with the carbonate rock resulted in the deposition of zinc-bearing minerals, including smithsonite, hemimorphite, hydrozincite, and hydrohetaerolite. Generally, these replacement orebodies were located just below the silver-bearing lead deposits (Heyl 1964).
California Gulch Superfund Site and Reclamation
On 8 September 1983, Leadville was added to the national priority list by the U.S. Environmental Protection Agency (EPA) as an official Superfund site and was designated the "California Gulch Superfund Site" (Klucas 2004). The Leadville mining district, which is located at a mean elevation of 10,150 feet, mined gold, silver, lead, copper, and zinc for 140 years, from 1859 through 1999. According to the EPA, the resulting mine rock and tailings from mills, containing pyrite and base-metal sulfides, had been dispersed over an area of 11.5 square miles, including the city of Leadville. The oxidized sulfides carried by snowmelt and thunderstorm runoff, along with acid mine drainage, released lead, arsenic, cadmium, silver, and zinc into the Arkansas River drainage system, polluting the river for many miles downstream.
As viewed by some, the mining scene in Stray Horse Gulch looked like the other side of the moon, with the Wolftone, Pyrenees, Greenback, Maid of Irwin, and Mahala mines being significant sources of pollution. The most enduring and harmful environmental result of Western mining is this type of pollution where metal-laden rusty- orange water issuing from mine openings eventually emptied into a river system causing pollution. After many years of battling with the residents of Leadville, the EPA finally drew up a reclamation plan; however, instead of conventional mine reclamation (where the mine dumps were flattened and capped with a plastic liner to keep water seeping into the pile and then were covered with topsoil and seeded to grow grass), another controversial plan was devised. The plan called for consolidating mine dumps into large cone-shaped piles and then capping them with "clean" dolomite mine dump rock from the Black Cloud mine that would neutralize any water seeping into them. A number of historic mine dumps would be destroyed in the process, and the plan was bitterly opposed by some residents of Leadville. On 31 July 1997, bulldozers and earth-moving equipment rolled into Stray Horse Gulch obliterating everything in their path and destroying part of Leadville's historic mining heritage (Klucas 2004). Bulldozers tore into the Wolftone, Mahala, and Maid of Erin mines in the summers of 1997 and 1998. In late summer 1998, the EPA finished capping and consolidating the dumps into three towering, tiershaped piles that were then capped with the whitish-gray crushed dolomite rock. The local residents dubbed the huge monochromatic piles "The Wedding Cakes," an allusion to the dolomite rock's resemblance to frosting on a three-tiered cake. It looked so out of place that in summer 1999, brown oxidized rock was dumped on the tiers and streamed over the edges, giving the piles a look of chocolate frosting dribbling down the sides of the white cake. After sixteen years of clean-up operations and millions of dollars spent on reclamation, the project was finally completed in 1999.
The 2,000-ton stockpile of oxidized zinc ore at the Wolftone mine was also hauled off to be consolidated into one of the huge piles, but there was such an outcry from local mineral collectors and historic preservationists that the rock pile was returned to the Wolftone mine location.
The Collectors Arrive
Prior to the start of reclamation in July 1997, the Wolftone mine dump and other dumps in Stray Horse Gulch had been favorite collecting sites for mineral collectors through the years. The Wolftone piles were well known for the small but fine hemimorphite crystal groups that had been recovered from the locality (Johnston 2000).
When the 2,000 tons of oxidized zinc ore was removed from its original location and then returned to the site, it had been completely churned up and reconfigured into a sloping pile about 30 feet wide at the base, 18 feet high, and about 70 feet long (Ed Raines, pers. comm., 2008). This did not escape the notice of collectors, and the dump was heavily collected on the weekends by the Micro Mineral Satellite Group of the Colorado Springs Mineralogical Society and other collectors. From late summer 1997 through the final phases of reclamation in 1999, collecting was at its best, and the pile produced hundreds of microcrystal specimens that were incorporated into micromount collections. Today, the pile is still there but has been somewhat flattened out from the heavy collecting. The small dump is accessible to collectors and is still producing specimens.
Mineralogy of the Oxidized Zinc-Ore Stockpile
The material that makes up the oxidized zinc-ore stockpile is composed of tan to chocolate-brown-colored rock that is composed of zinc carbonates and silicates along with iron and manganese oxides, which give the rock its distinctive color. The ore has retained some of the original lithologic features of the Leadville Limestone and is generally hard and compact. Numerous small vugs occur throughout the ore. They typically show thin, somewhat smooth and shiny layers of iron and manganese oxides that have been deposited in the vugs. Late-stage secondary ore and gangue minerals were deposited in the vugs, forming beautiful microcrystals.
Johnston (2000) lists thirty confirmed and unconfirmed species that were collected from the oxidized zinc-ore pile from 1997 through 1999 by members of the Colorado Springs Mineralogical Society. Identification was primarily by visual examination along with XRD and SEM. The following species have been positively identified. They are described because they occur as crystals suitable for micromounts and can still be collected from the ore pile.
Barite, BaSO^sub 4^, is rare and occurs as thin, clear, tabular crystals singly and in groups that range to 4 mm.
Calcite, CaCO^sub 3^, has been found as clear to cloudy, sharp, steep rhombohedra to 2 mm. Many of the crystals show a pseudocubic habit and are scattered on a limonite matrix.
Cerussite, PbCO^sub 3^, is rare in the oxidized zinc ore but is occasionally found as beautiful, complex, clear crystals to 3 mm in length.
Desclozite, PbZnVO^sub 4^(OH), is one of the rare minerals that has been identified in the oxidized ore from the mine. Early specimens that were collected consisted of reddish-brown globs of microcrystals perched on a limonite matrix (Rosemeyer 2006). In 1997, superb microcrystals consisting of discrete, tiny, honey- colored crystals scattered on limonite, were collected from the stockpile. Some of the specimens have a thin coating of drusy quartz on the desclozite.
Gypsum, CaSO^sub 4^*2H^sub 2^O, occurs as clear to white microcrystals as a secondary overgrowth on limonite and earlierformed minerals.
Hematite, alpha-Fe^sub 2^O^sub 3^, occurs as thin, shiny black, microsized pseudohexagonal plates stacked on a goethite/limonite matrix. It also occurs as rosettes of platy microcrystals associated with smithsonite.
Hemimorphite, Zn^sub 4^Si^sub 2^O^sub 7^(OH)^sub 2^*H^sub 2^O, is a common zinc silicate making up a high percentage of the oxidized ore in the Wolftone mine. Many historical collections contain beautiful crystallized groups of clear to white, striated crystals to several centimeters in length. During the reclamation period, many exceptional microspecimens were recovered from the stockpile.
Pyrolusite, Mn^sup 4+^O^sub 2^, occurs as groups of divergent needlelike, lustrous black crystals up to a few millimeters long that occur scattered on a limonite matrix.
Quartz, SiO^sub 2^, has been noted as drusy microcrystalline coatings on other minerals, especially desclozite and smithsonite.
Smithsonite, ZnCO^sub 3^, is probably the second most common zinc- bearing mineral at the Wolftone mine, where it occurs in a variety of habits in the oxidized ore. The most notable and collectible form is as clusters of rhombohedra, which have been called "stacked rhombohedra" in the literature (Johnston 2000). The crystals range in color from clear to white to pale blue and are up to 2 mm in size. Grayish-white "rice-grain" crystals of smithsonite to 1 mm long occur in vugs. Rice-grain crystals have also been collected that have been replaced by limonite and show a hollow interior.
Two new mineral species were named after the discoverer of the oxidized zinc ores and the mine itself but were later discredited. As mentioned, nicholsonite was named after Samuel D. Nicholson and was thought to be a zincian variety of aragonite. It occurred in the oxidized iron-manganese ore of the "blue limestone" (Leadville Formation). It was later found to be aragonite (Eckel 1997). Wolftonite was described from the Wolftone mine but was later identified as hetaerolite; further study by Frondel and Heinrich (1942) established it as hydrohetaerolite.
I especially thank Dorothy Atlee who brought to my attention the microcrystals collected from the Wolftone mine's oxidized zincore stockpile and asked me to write this article on the locality. She also made a substantial contribution to the color fund to make possible the color spread in the article. My gratitude is also extended to Phil McCollum (PM Graphics), who, on only two months' notice, made special trips to sort through Dorothy Atlee's extensive collection of Wolftone mine micromounts and select the best specimens for photography. Ed Raines provided historical information and lively discourses on the California Gulch Superfund Site reclamation operations. William Besse prepared the maps. Dr. Virgil W. Lueth, Dr. Robert B. Cook, Ed Raines, and Robert Stoufer reviewed the article and offered literary and technical revisions.
All microcrystal photos by Phil McCollum of specimens in the Dorothy Atlee collection, unless otherwise noted
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Tom Rosemeyer has mined and collected minerals in the San Juan Mountains for the past thirty-five years and is now retired from the mining industry. He is a frequent contributor to Rocks & Minerals.
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