The Mines and Minerals of Leadville

Mining

Two poor German shoemakers, August Rische and George Hook, who had been grubstaked by Tabor (Blair, 1980), “happened to sink a hole where the 'contact or the mass of the ore approached the surface and found the ore body on which was developed the Little Pittsburg mine, the foundation of the fortune of H. A. W. Tabor" (Henderson, 1926). On May 15, 1878, they “struck carbonate ore that ran 200 ounces of silver to the ton” (Blair, 1980). By 1882 production had increased to an output valued at $10,139,765 (Henderson, 1926). This value was based on a per-ounce price of $1.14.

During 1883 “Iron Hill continued to be the largest producing district from the Iron Silver, A. Y., Minnie, Colonel Sellers, Tucson and other mines. The Little Jonny mine was actively worked, the product being silver-lead ores carrying some gold” (Henderson, 1926). “In the first decade of the carbonate era, 1879-1888, it produced $146,342,000 in silver, lead, gold and copper" (Warwick, 1905).

It was also in 1883 that a visitor to Leadville could see the Leadville Free Museum. "It is a rare treat, and one that every visitor to Leadville should avail himself of, to see the mineral and natural curiosities and the mercantile museum of Messrs, Westover and Fuller. They have every imaginable mineral wonder mounted and unmounted that is known to Colorado, which is the same as saying ‘which was ever known to the world.' They also carry a large collection of petrified woods of every imaginable shape and uniqueness. . . . Messrs, Westover and Fuller have had many years valuable experience in their present line of business, and are continually adding new and rare specimens to their collections. They not only supply rare articles to residents for their own use or to send eastern friends and furnish every eastern visitor with souvenirs, but fill orders from metropolitan jewelers, colleges, private collectors, etc." (Leading Industries of the West, 1883).

Leadville Miners Candlesticks

“In 1890, a large deposit of copper ore was found in the Henriette and Maid of Erin properties. In 1893 Lake County began to produce considerable gold, chiefly from properties on Breece Hill." In that same year, "American Smelting and Refining Company organized and took over nearly all lead smelters of the Rocky Mountain States" (Henderson, 1926).

After the fall in the price of both silver and lead in the early 1890s and a disastrous miners' strike in 1896, it took a cooperative effort from the town of Leadville to revive mining there. The DownTown Pumping Association was formed to assist with the financing necessary to drain the "downtown” mines, which had been flooded during the strike. The Home Mining Company, supported largely by Leadville merchants, was also organized. The success of these organizations encouraged miners and restored prestige to the district (Warwick, 1905).

During the period from 1899 to 1915, zinc became the important mining product of the Leadville area. Zinc mills were established and shipments of zinc sulfides became quite large. Numerous large bodies of zinc carbonate were found in 1910, many in the old workings.

Stacks of silver bullion at a Leadville mine
Sixty-five tons of silver bullion awaiting shipment at Leadville. Photo (one side of a stereo pair) by Gurney, printed by Kilburn Brothers, Littleton, New Hamphshire; authors` collection.

In 1915 "output of gold from Breece Hill mines increased greatly and the placer industry was revived, after years of non-existence, by the installation of a dredge on the Arkansas River at the mouth of Box Creek, 12 miles above Leadville. In June, 1916, the downtown mines, which had been allowed to fill with water in 1907, were again unwatered and from 1917 to 1923, when they were again closed, they produced large quantities of lead oxide, zinc carbonate, iron-manganese and other ores. In August, 1923, unwatering by electric pumps was begun in the Carbonate Hill mines that had been closed in 1918-1919. The water was not completely removed until the spring of 1925” (Henderson, 1926).

The years between 1918 and 1940 saw many ups and downs in the mining at Leadville. Several small booms took place during these years, brought about by a demand for some of the metals or a chance discovery of a new pocket or small orebody, but these always seemed to play out, resulting in a period of inactivity.

Mining became active once again as a result of the demand for metals during World War II and on into the Korean conflict. In 1943 the government appropriated money for a 4-km drainage tunnel to drain the Leadville district. It was hoped the tunnel would open large deposits of lead, zinc and manganese ores for production, but the project was halted in 1952 because of rising costs and a decline once again in metal prices.

1895 Leadville gold exhibit
An 1895 exhibit of crystalline gold, sponge gold, placer gold, and gold bullion taken from Leadville mines. The specimens and bars, worth $150,000 then and at least 2.5 million today in bullion value alone, were assembled and exhibited by the Carbonate National Bank, Leadville. Courtesy University of Colorado Western History Collection.

In recent years mining has been carried on with the discovery of a block of down-faulted ore near the old Black Cloud lode claim and is being worked through the new Black Cloud shaft. “The Hilltop mineral deposit and veins common to Park and Lake Counties are being worked through the Sherman Tunnel” (Holmes, 1983).

“In some respects, Leadville is the most remarkable city the world has ever seen” (Ingham, 1880). Certainly it has been able to survive the vicissitudes of fortune for more than a century, and it remains a working monument to mining in Colorado.

Geology

Ridge (1972) has summarized the geology of the Leadville area, and his report is the basis of the following synopsis.

The Leadville area is underlain by Precambrian granite, gneiss and schist which are essentially free of ore. Overlying Paleozoic sediments (quartzite, shale, dolomite, sandstone, limestone) all have been found to contain ore, although the Mississippian Leadville dolomote has been the biggest producer. A wide variety of intrusive rocks, mostly porphyries, have penetrated the sediments at one time or another. One unit, the Pando porphyry, forms extensive sills up to 300 meters (1000 feet) in thickness. Many of these intrusions were pre-ore, but some were post-ore, and dating of these rocks suggests that the Leadville ores were emplaced in the late Mesozoic or early Tertiary.

Most of the Leadville ore mined has come from an area bounded by Leadville on the west, the Ball Mountain fault on the east, Evans Gulch on the north, and Iowa Gulch on the south. Nevertheless, significant quantities have come from some outlying areas.

The primary ores at Leadville are of three types: (1) silicate-oxide deposits, (2) mixed-sulfide veins, mostly in siliceous rocks, and (3) sulfide replacement bodies in dolomite. Several periods of faulting prepared the way for introduction of the ore-forming solutions throughout the area.

The silicate-oxide deposits, of relatively minor economic significance, consist primarily of magnetite and hematite in a serpentine-manganosiderite gangue. Subsequent fracturing of this assemblage allowed the formation of gold-bearing pyrite veins.

The mixed-sulfide veins, most common in the eastern area because of the abundance of siliceous rocks there (which the veins seem to favor), consist of pyrite with interstitial chalcopyrite and gold in quartz gangue. Gold, silver and copper have been mined extensively from these deposits, particularly where the ore has undergone some secondary enrichment. In some areas the veins expand into sulfide replacement bodies.

The sulfide replacement deposits are more common in the western part of the district, where carbonate rocks suitable for replacement are more abundant. These bodies form mantos spreading out from fractures and sheeted zones under impermeable covers such as porphyry sills. The replacement ores consist primarily of sphalerite and galena with appreciable silver, all in a gangue of manganosiderite with quartz and barite. The most abundant sulfide was pyrite, its deposition beginning before and ending after the formation of sphalerite and galena. Only very small amounts of gold and silver are found in this ore; but considerable amounts of a different assemblage occur irregularly throughout the replacement bodies. This assemblage consists of chalcopyrite (most abundant), hessite (Ag2Te), altaite (PbTe), argentite, gold, and a peculiar silver-bismuth-rich variety of galena which is consistently near Pb11Ag11Bi11S15 in composition.

Principal faults and ore bodies at Leadville.
Principal faults and areas of principal ore bodies at Leadville. Dot-pattern: Pliocene and Pleistocene deposits. Hachured line: top of basement (Tweto, 1968).

Replacement bodies occur all over the district, but those in the outlying areas tend to be smaller and simpler in their mineralogy.

Deposition in the Leadville area as a whole spans a range of temperatures and pressures. The magnetite-hematite ores are most certainly hypothermal; the high-grade replacement bodies appear to be mesothermal; the so-called bismuth-stage assemblage is a typical leptothermal suite; and deposits in the more distant areas are clearly telethermal.

Thompson et al. (1984) provides the most recent discussion of hydrothermal ore genesis at Leadville. However, DeVoto (1984) proposes some alternative concepts by theorizing that pre-existing karst (cavernous) topography within the limestone units controlled ore deposition in a manner similar to that associated with Mississippi Valley-type lead deposits.

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