Part 6

Development of the metal-mining areas in Colorado followed a definite sequence. Placer gold was usually discovered first. Recovery of placer gold was followed by mining of gold from veins or “lodes.” Although at first only native gold was mined, gold-bearing compounds such as telluride were soon recognized as an additional source, especially at Gold Hill, Cripple Creek, and of course the camp that came to be known as Telluride. As gold sources were depleted, silver, first produced as a byproduct, became of prime interest. Lead and zinc were in turn byproducts of silver mining. Other metals, notably copper, vanadium, tungsten, and iron, were produced later. Molybdenum is the Johnny-come-lately of the state’s mining industry, but is now the chief metal produced. A uranium boom in the 1950s brought a short rush to western Colorado and new vigor to the economy.

Oil was discovered near Canon City in 1862. The nearby Florence field and a small, shallow field near Boulder preceded much greater discoveries in the Denver Basin, the Uinta Basin, and southwest Colorado. Oil reservoirs, confined to areas of sedimentary rock, are found primarily in the Prairie and Plateau Provinces of the state, and recovery of the oil has done much to distribute population to these areas.

Coal is also restricted to sedimentary rock areas. Coal production in Colorado has waxed and waned with the years, but has provided fuel for export, for the railroads, for the manufacture of electric power, and for many of the state’s industries.

A good picture of present mineral production in Colorado can be obtained from the following summary for 1971, prepared by the Colorado Bureau of Mines:

Product Value

Molybdenum $105,389,456 Petroleum 90,494,459 Sand and gravel 32,842,503 Coal 30,251,443 Natural gas 18,695,225 Uranium 18,048,692 Vanadium 15,863,554 Cement 13,377,520 Zinc 13,310,787 Lead 6,582,025 Tungsten 6,360,020 Limestone and dolomite 5,397,570 Silver 4,198,054 Fluorspar 3,887,210 Copper 3,875,976 Stone 1,961,279 Gold 1,832,791 Clay 962,986 Iron 880,047 Pumice 309,370 Tin 278,862 Gypsum 253,856 Pyrites 142,640 All others 1,091,927 Total ($376,288,252)

Colorado is now the nation’s leading producer of molybdenum, tin, and vanadium, and second in output of tungsten. In oil production it ranked twelfth among the states in 1968, but ninth in reserves, with 420,000,000 barrels of proven reserves on 1 January 1969. An as yet untapped source of oil lies in the oil shales of western Colorado.

As part of the natural environment, water plays a major role in man’s activities. Water problems in Colorado revolve mainly around the best use of runoff in a state whose major catchment basins are across the continental divide from her largest population centers and most fertile farm land. Groundwater, closely related to surface water distribution and movement, is a geological problem, and in Colorado as in other states many government and private geologists serve farm and industrial communities in the search for usable supplies.

CAUTION: Old mines are dangerous! They may contain water or deadly gases, or be on the verge of collapse. Keep away from abandoned prospect pits and mine shafts. WARN AND WATCH YOUR CHILDREN.

GOLD, SILVER, AND OTHER METALS

Colorado’s placer and lode sources of gold, which gave first impetus to the series of mining booms in the state, were fantastically rich. Summit and Lake Counties, for instance, each produced more than $5,000,000 in placer gold between 1859 and 1867. During the same nine-year period, more than $9,000,000 in lode gold was produced from Gregory Gulch, a tiny canyon between Central City and Black Hawk. Other districts rivalled or surpassed these figures.

Early in the game it was recognized that almost all the deposits occurred along what came to be known as the “mineral belt,” a fifty-mile-wide zone extending southwest from the Boulder region. Most of the metals mined in the state come from this belt, but there are three notable exceptions: Cripple Creek, Silver Cliff, and western Colorado vanadium and uranium districts. In the first few years of the Colorado rush, gold ores and placer gold were discovered only in the northeastern part of the mineral belt. Gradually the belt was found to extend further and further southwest: Tincup was discovered in 1861, Silverton in 1870, Lake City in 1871, and Telluride in 1875. Aspen, on the western edge of the belt, was not discovered until 1879, perhaps because the area was difficult of access and lacked the easily recognizable native gold.

In the northeast part of the mineral belt, gold and other minerals occur in veins in Precambrian granite and gneiss. In the Leadville and Aspen areas, ores are associated with altered Paleozoic limestones. At the southwest end of the mineral belt, in the San Juan Mountains, ore veins are found near or in Tertiary volcanic rocks. Native gold, gold-bearing compounds, and other metallic ores in these veins originated where mineral-rich solutions from deep within the earth penetrated fissures and joints in the surrounding rock. Regardless of the age of the host rock, almost all the ores of Colorado were deposited in the early or middle Tertiary Period, about 35 to 70 million years ago.

Gold and silver are no longer mined extensively in Colorado, although any summer Sunday will see weekend operators panning near mountain streams or trundling rock from one-man mines. The recent rise in the price of silver has encouraged many miners to reopen old shafts. The most active mines in the state today are those producing molybdenum, lead, zinc, and vanadium. (Vanadium, although a metal, usually occurs in Colorado with radioactive minerals, and so is discussed with them rather than with the metals.)

Telluride Denver Colorado Springs Alamosa BOULDER Ward Gold Hill Boulder Nederland GILPIN Central City Black Hawk JEFFERSON Golden CLEAR CREEK Empire Georgetown Silver Plume Idaho Springs SUMMIT Breckenridge EAGLE PITKIN Aspen GUNNISON Tincup CHAFFEE PARK Climax Alma Como Fairplay TELLER Cripple Creek FREMONT OURAY Ouray Camp Bird Ironton SAN JUAN Silverton HINSDALE Lake City LA PLATA Durango MINERAL Creede CUSTER Silver Cliff

All told, some 430 metal mining districts have been established as legal entities in the state of Colorado. Each of these districts had the right to draw up its own regulations concerning prospecting, claims, and mining rights, within a framework established by the Federal government. Only a few of the districts ever became really significant producers. The geology and history of several of the leading areas are presented in the pages that follow.

Boulder County

Gold Run, near Gold Hill, was the scene of one of the earliest strikes in Colorado. Gold was found here in December 1858, and was sluiced from stream sands and mined from veins early in 1859. Active placer mining lasted only about a year, however, and lode mining dropped off rapidly as near-surface oxidized ores were worked out. When a smelter was erected at Black Hawk in 1868, and sulfide ores could be treated, there was a revival of activity. In 1869 the Caribou and Poorman mines near Nederland were discovered; they quickly became the most active mines in the county. The Ward district opened soon after.

In 1872, a gold-silver telluride called petzite was found in veins at Gold Hill. Renewed prospecting in this area resulted in location of mines near Sunshine, Salina, and Magnolia. During the years that followed, new mines appeared almost as fast as old ones were depleted. In 1892, the peak year, more than $1,000,000 in gold and silver was produced; total production has been about $25,000,000.

In 1900, a black mineral common in the Nederland area was recognized as ferberite, an ore of tungsten, and a new rush to the area started. During the next eighteen years Boulder County was the main tungsten producer in the United States; about 24,000 tons of tungsten trioxide, worth $23,000,000, were produced here. The ore was found in nearly vertical veins six inches to three feet thick, in a lenticular area about nine miles long extending from Nederland northeast to Arkansas Mountain, four miles west of Boulder.

Boulder County is characterized by an abundance of small mines. Old shafts, pits, and mine buildings can be found throughout the central part of the county. Little mining is done here today; many of the towns that once peppered these hills have fallen into decay or disappeared entirely.

Central City and Idaho Springs

The Central City-Idaho Springs area was the principal metal mining region in the state until the late 1880s. In 1858, rich placer deposits were discovered in gravels and river terraces along both forks of Clear Creek. Exploration upstream led to discoveries of rich oxidized quartz veins at Central City, Black Hawk, and Idaho Springs. These veins, which generally trend northeast-southwest, extend through the mountains in a zone about six miles long and three miles wide between the two forks of Clear Creek.

The ores filled a multitude of cracks and fissures in the Precambrian bedrock. The veins are usually less than five feet thick, and are almost vertical and often clustered in zones up to thirty feet wide. The position of one of the vein systems may be seen clearly between Black Hawk and Central City—the ore-bearing rock has been mined out, but a series of collapsed tunnels marks the line where the veins crossed the valley. A monument here commemorates the discovery of Gregory Gulch, one of the richest localities in the state.

Several rich veins were mined in both directions—southwest from Central City and northeast from Idaho Springs—until the mines met. The Argo tunnel, marked by dilapidated buildings and extensive dumps on the north side of Idaho Springs, connected the two districts; it was completed in 1904.

The “Patch,” a deep crater-like hole on Quartz Hill, about one mile southwest of Central City, is an intriguing feature in this area. It was produced by glory-holing, a mining technique in which a deep tunnel is deliberately caved by blasting, so that ores above the tunnel can be removed. This glory hole was dynamited below an irregular mass of highly broken rock where many ore-rich veins converged. After the caving, ores were taken out through the remaining part of the tunnel.

The principal ore minerals of Central City and Idaho Springs are native gold, pyrite, sphalerite, galena, chalcopyrite, and tennantite. Prospecting for uranium was carried out during the 1950s but no uranium was ever mined here.

The area has produced almost $200,000,000 worth of gold, silver, lead, zinc, and copper. A few mines still operate seasonally or on a small scale, but tourists, many of them riding Jeeps across the mountainous terrain to visit mines and ghost towns, are often more visibly active than the mines.

Georgetown, Empire, and Silver Plume

A few miles southwest of Idaho Springs, another mining area had a similar, though less productive, history. In 1859, placer and lode gold were discovered near what is now Georgetown. Placer mining dominated here between 1859 and 1863. Gravel and crushed rock from decomposed quartz and sulfide veins were washed through sluiceboxes in the same way as placer gravel, gold being caught in riffles or gunny sacking on the bottoms of the troughs. The veins were found to be decomposed to depths of about 40 feet; below this the gold occurred closely associated with sulfides such as pyrite, sphalerite, galena, and chalcopyrite, from which it could not easily be separated. However, smelters were developed in 1866 for treatment of these sulfides, and gold, silver, lead, and copper were recovered. Gradually, as the gold was worked out, silver and lead became the important products of the mines.

Leadville

Placer gold was discovered in 1859 in California Gulch, about seven miles north of the present town of Leadville. The rush that followed was short but sweet; the camp was called Oro—gold! About $5,000,000 was produced from the placer mines within two years, though by 1861 the area was all but deserted, for the easily won placer gold was gone.

In 1875 a smelter was erected a few miles downstream from Oro to process cerussite—silver-rich lead carbonate—that occurred in the placer sands. For years this mineral had been considered a nuisance because, being much heavier than sand, it tended to separate out with the gold. The new town of Leadville sprang up near the smelter and shortly afterward more lode deposits were discovered south of the placer workings. From $63,000 in 1875, production climbed to $2,500,000 in 1878 and more than $15,000,000 in the peak year of 1882.

Geologically, the ores of this district occur as Tertiary replacements and veins in Ordovician, Devonian, and Mississippian limestones. The “Blue” or Leadville Limestone, of Mississippian age, contains the richest ore. Ore deposits were formed after the limestones had been faulted and cracked extensively by mountain-building movements; the ores themselves probably crystallized from molten or gaseous materials involved in related igneous intrusions. River gravels and glacial debris mask the true nature of the lode deposits, but studies in the mines show that the fault systems along which ores are deposited trend north or north-northeast.

The Leadville district is now experiencing its third mining boom as a newly recognized lead-zinc orebody is being developed. Production is expected to reach 700 tons of ore per day by 1971. Total production of gold, silver, lead, zinc, and copper in the district has reached $500,000,000.

Breckenridge

Breckenridge was also discovered in 1859, with placer gold the first attraction. The placers gave out in 1862 after about $3,000,000 in gold had been recovered. Earliest attempts to mine the rich silver and lead veins of the district were in 1869.

As at Leadville, the sedimentary rocks of the area were intruded by granitic masses in Tertiary time, but here the sedimentary rocks are mostly Pennsylvanian sandstones and shales. These rocks were badly faulted and broken during the intrusion, and the ores were deposited as the granitic material cooled. The lode deposits occur mostly in small veins well hidden by surface sands and gravels. Some of the veins yielded exceptionally beautiful crystallized wire and flake gold, specimens of which are on display at the Colorado School of Mines library in Golden and in the Denver Museum of Natural History.

Dredging for alluvial gold was attempted in 1898 in the Breckenridge district, but this method of extracting gold was not successful until 1905. A number of dredges operated between 1910 and 1925. These floating behemoths shovel up gold-bearing gravels from the bottom and one side of the pond on which they float, sort out the gold in giant sluiceboxes, and spew out the leftover gravels in great arc-shaped heaps that can be seen near Breckenridge and Fairplay and in a number of other valleys in Colorado. They depend for their operation on a plentiful supply of water and a shallow water table, but they can sift through quantities of gravel at relatively low cost. All told, about $7,000,000 in gold has been dredged from this district.

Fairplay

Another gold field discovered in 1859 was in the northwest corner of South Park, along the headwaters of the South Platte River. Several mining camps were established here. After early production of rich placer deposits, claims were consolidated and large flumes constructed so that gold could be recovered by hydraulic mining. In this type of mining, streams of water from high-pressure hoses are directed at gravel surfaces. The gravels are washed into long sluiceboxes, where gold is caught in riffles. Hydraulic mining continued upstream from Fairplay until about 1900.

In 1922 a dredge was constructed near Fairplay to process gravel along the South Platte and in the valley floor. An even larger dredge, constructed in 1941, operated until 1952, when rising labor costs overrode the narrow margin on which it operated. At the time operations ceased, the dredge was recovering about six cents in gold for each cubic yard of gravel processed.

Placer gold has always been the principal mineral product of the Fairplay area, but native gold also occurs in the surrounding mountains in quartz veins, and many small mines were developed to extract it. Sulfide ores were also mined; they contained silver, lead, and zinc as well as gold. In the Mosquito Pass and Horseshoe Amphitheater areas, there is renewed activity now because of the recent rise in the price of silver.

Silverton

Gold was discovered in the San Juan Mountains of southwest Colorado in 1870. The earliest mine, near what is now Silverton, was located by a group of prospectors sent out by Governor Pile of New Mexico Territory. Since the site was on Ute Indian land, real mining did not begin until a treaty allowing it was ratified in 1874.

Production in the Silverton district has been from veins in Tertiary volcanic rocks within an elliptical area known as the Silverton cauldron. Here the volcanic rocks, part of the several thousand feet of lava flows and ash falls of the San Juan volcanic field, were cracked and faulted by a second period of igneous activity. Ores formed in the cracks and fissures.

In the 1870s the Silverton district was very remote, and difficulties with transportation retarded activity there. In 1882, however, a narrow-gauge railroad was built connecting Silverton with Durango, and the problem of transporting ore out of the isolated mountain valley was simplified. The railway still exists; a train makes daily passenger runs during the summer—the only remaining operating narrow-gauge line in the United States. The track follows the Animas River canyon, whose cliffs and crags are dotted with long-abandoned mines, prospect holes, and mine buildings, monuments to the tenacity and determination of the men who mined here.

Production in this district was more than $22,000,000 in gold and $20,000,000 in silver between 1874 and 1923. New activity is evident here, as in other silver-rich areas of Colorado, because of recent demand for silver, lead, and zinc.

Ouray

Ouray was settled in 1875, when gold and silver deposits were found near Mount Sneffels. Since 1877, mines in Ouray County have produced over $35,000,000 in gold and $32,000,000 in silver. The district is still quite active: in 1965, mines in this area produced more than $9,000,000 in gold, silver, copper, lead, and zinc, about a third of total Colorado production of these metals for that year.

A mile north of Ouray a prominent intrusive stock marks the center of mining activity closest to Ouray. The richest deposits of the Ouray area, however, lie about five miles southwest, near Mount Sneffels and Red Mountain Creek. There, several large mines, including the famous Camp Bird mine, have operated for many years, extracting ore from hundreds of veins that underly the surface. Some of these veins are two to four miles long. They are in Tertiary volcanic rocks of the San Juan Formation. Quartz and calcite are the common gangue (non-economic) minerals, and pyrite, sphalerite, galena, and chalcopyrite are the most abundant ores. Most of the silver is in the galena; gold occurs in streaks and nodules associated with quartz.

About ten miles south of Ouray, along the “Million Dollar Highway” (U. S. 550), the Red Mountain district lies on the northwest edge of the Silverton volcanic cauldron. It contains a number of small pipelike bodies very rich in silver-copper and silver-lead ores. Following the mid-Tertiary volcanism and ore intrusion, surface rocks in this area were intensely oxidized: resulting iron oxides now form the gaudy reds and yellows of Red Mountain and the slopes near Ironton. This alteration, as well as the fact that much of the area is covered with fallen rock, stream gravels, or glacial deposits, compounds difficulties of locating the small though high-grade ore deposits.

The Idarado Mine, on the east side of U. S. highway 550 near Red Mountain, used to produce ores from nearby volcanic pipes; now it produces from veins some distance to the northwest. The area is honeycombed with tunnels and shafts.

Aspen

Silver was found at Castle Creek and on Aspen Mountain in 1879. A group of prospectors from Leadville, apparently after examining maps of the Geological and Geographical Atlas of Colorado published in 1877, explored along the line of Paleozoic limestones encircling the Sawatch Range. As they had hoped, they found ores similar to those at Leadville in rocks of the same age.