Miners came to Colorado for gold, stayed for silver, and survived after the 1890s by diversifying into a wide range of base and industrial metals such as lead, copper, zinc, molybdenum, tungsten, vanadium, radium, and uranium. Often ignored or discarded during early prospecting and mining, these base and industrial metals helped sustain mining operations after the silver crash of 1893.

Production of these metals typically started in the 1870s or 1880s, increased in the 1890s and 1900s, and experienced later peaks as prices surged with high demand during the world wars. Most mining died out after World War II, but the Cold War spurred ongoing molybdenum production and a uranium boom. Today molybdenum has become the most important metal in Colorado, with giant mines operating in Lake and Clear Creek Counties.

Types and Uses

In contrast to precious metals such as gold and silver, which are highly valued for their own sake, base and industrial metals tend (with some exceptions) to be worth less and are valuable mainly for their commercial and industrial uses.

Lead is used in bullets and batteries and has a wide variety of applications in construction, though its dangerous health effects have caused it to be phased out of pipes, paints, and gasoline. Copper’s high conductivity makes it ideal for electrical uses, especially as a wiring material. Zinc forms a number of useful alloys and compounds, such as brass (made with copper) and zinc oxide (used as a white pigment and in mineral sunscreens); on its own, it prevents corrosion in batteries and on iron and steel through galvanization. Molybdenum, tungsten, and vanadium are used primarily to harden or toughen steel.

Radium is highly radioactive and was used in the early twentieth century for illumination and as a cancer treatment. Uranium is less radioactive and was regarded as a waste product until World War II, when it became a key ingredient in nuclear weapons and, later, nuclear power plants.

Formation and Location

In Colorado, the mineral-containing rock known as ore was originally formed during the uplifts of the Ancestral Rocky Mountains (300 million years ago) and the modern Rockies (70–45 million years ago). Superheated magma rose into rocks deep under the surface, creating pressure and rising through faults and fissures. As the magma solidified, it took the form of mineralized bands called veins.

As a result of this origin, most of Colorado’s metals occur in a diagonal belt stretching roughly from Boulder County to the San Juan Mountains. The main outliers are radium, vanadium, and uranium, found primarily on the Colorado Plateau near the Utah border, especially in and around the Paradox Valley. In general, the areas with the greatest production of precious metals such as gold and silver have also yielded the largest amounts of base and industrial metals such as lead, copper, zinc, and molybdenum. Lake County dominated the production of all these metals, with the San Juan region also contributing. Tungsten production was concentrated in Boulder County.

Early Decades

During the early decades of Colorado mining, prices for base metals were usually quite low compared to the precious metals that drove the boom: four to eight cents per pound for lead, three to thirteen cents per pound for zinc, and as much as a quarter per pound for copper. These low prices meant that as long as gold and silver retained their shiny luster, base and industrial metals remained largely byproducts recovered from the pursuit of precious metals but not worth seeking out on their own.

Because lead was often bound up with silver and had various industrial applications, it saw the earliest and largest production among Colorado’s base and industrial metals. Lead was shipped from Gilpin, Clear Creek, Summit, and Park Counties starting in the early 1870s, after techniques for silver-lead smelting were developed. The discovery of silver-bearing lead carbonates in Leadville later that decade caused Colorado’s lead production to soar; by 1880, Leadville led the world in silver-lead smelting. Lake County dominated the state’s lead production throughout the 1880s and 1890s, with Pitkin County and the San Juans making significant contributions as well.

Copper was an early byproduct of ores in Gilpin and Clear Creek Counties. In the 1870s, mines in Park County and the San Juans started to produce some copper as well. One of the state’s few large copper mines opened north of Salida in 1884, and production ramped up even more when Lake County began to ship copper in 1889. Zinc production did not begin in Colorado until the mid-1880s. A zinc oxide plant built at Cañon City led to an increase in the 1890s. Much of the zinc came from Lake County, but Eagle and Summit Counties also shipped some.

The collapse of the silver market in 1893 led many Colorado mines to diversify their production to survive. Overall, Colorado’s mining production peaked in 1900 before entering a period of gradual decline. Within that decline, base and industrial metals became even more critical as ballast to help mines stay afloat as precious metals saw lower prices and lower yields. Colorado’s copper production, for example, climbed to a peak in 1909. Zinc boomed in the early 1900s before declining after the Panic of 1907. Production surged again with the discovery of zinc carbonate at Leadville in 1910, allowing zinc to displace lead as the area’s primary base metal.

World Wars

The start of World War I in 1914 generated massive demand for base and industrial metals as countries competed to develop massive, armored militaries. Prices for lead, copper, and zinc surged to new highs. Zinc production hit a new peak in 1916, with 134 million pounds bringing in some $18 million. Copper production did not beat its previous peak, but its value crested to more than $2 million annually.

World War I also stimulated demand for previously little-mined metals used to harden or toughen steel: tungsten, molybdenum, and vanadium. During the war, Colorado became the world’s top producer of tungsten and molybdenum. Tungsten had been part of the state’s production since 1900, when it was identified in western Boulder County. Soon Caribou had the largest tungsten mine in the world. During the war, the price of tungsten shot up by a factor of twenty, and tons of new mines opened in the area.

Farther west, molybdenum was first identified at Bartlett Mountain in the mid-1890s, but it had little commercial value until World War I. The Bartlett Mountain deposit—the world’s largest—saw a rush of claims after 1915. In 1918 the Climax Molybdenum Company opened a mine at Bartlett Mountain and quickly developed it into the state’s largest mine. The company bought up claims from its competitors when demand declined at the war's end. Climax sat idle for several years, but soon the marketing efforts of company head Brainerd Phillipson generated new demand from automobile makers and other industrial users. By the mid-1930s, Climax accounted for an astonishing 86 percent of world molybdenum production.

Vanadium had been identified in Colorado in 1898, when an ore called carnotite in the Paradox Valley was found to hold vanadium, radium, and uranium. Vanadium saw limited production in the early twentieth century, but as with tungsten and molybdenum, demand skyrocketed during World War I. By the early 1920s, Colorado had shipped some 500 tons of the stuff. Production declined after the war. During the Great Depression, when the development cost was low, the United States Vanadium Corporation bought up vanadium-producing properties, revived old mills, and established new towns at Uravan and Vancorum. Production remained limited, but the infrastructure proved helpful when demand for vanadium ramped up again ahead of World War II.

Among the carnotite metals identified at the turn of the century, radium was the most immediately useful; it provided nighttime illumination and was valued for experimental cancer treatments. Western Colorado soon became the world’s leading producer of radium, and in the 1910s, the National Radium Institute built a concentrator near Naturita and a plant in Denver. During World War I, prices for radium soared when supply from Austria was cut off in Allied countries. At the same time, demand increased as militaries scrambled for radium to light up instrumentation at night. Radium briefly became the most expensive substance in the world, going for more than $3 million per ounce. Yet Colorado’s radium industry quickly died out after World War I, when demand dropped and new deposits were discovered in the Belgian Congo.

After a period of slow production during the Great Depression, the onset of World War II once again supercharged base and industrial metal mining in Colorado. Lead, zinc, tungsten, and vanadium surged for a few years, but this time the most lastingly important metals were molybdenum and uranium. At Climax, the War Production Board gave the molybdenum mine the highest operating priority in the country and posted a US Army Auxiliary Military Police unit there. The company shipped a total of 180 million pounds of molybdenum during the war.

Meanwhile, the race to develop an atomic bomb made uranium go from trash to treasure. In 1943 the Manhattan Project built a mill in Uravan to rework old tailings from western Colorado and Utah in search of material for bombs.

Cold War

After World War II, most mining in Colorado closed down for good. Some zinc production survived near Red Cliff and Leadville into the 1950s, and the Idarado Mine in the San Juans continued to ship lead, copper, and zinc. The main action, though, was in molybdenum and uranium, which remained in high demand as the United States shifted to permanent military preparedness in the Cold War.

With the United States competing against the Soviet Union for nuclear supremacy, the federal government sponsored a uranium rush. By the mid-1950s, the Colorado Plateau had about 800 mines, and Colorado was the country’s largest uranium producer. The state’s uranium boom proved brief, however, as new mines came online in New Mexico and Wyoming. The rise of nuclear power plants resulted in another increase in production in the 1960s.

Throughout the 1950s and 1960s, Climax shipped huge amounts of molybdenum for military and industrial use. The company employed more than 1,000 workers, had a company town of 1,500 residents, and shipped more than 10 million tons of ore per year from the largest underground mine in the world. Even as it dominated the world market, accounting for 61 percent of world supply in 1963, it continued to expand, detonating the largest underground explosion in mining history in 1964 in order to break new ore from the mountain.

Health and Environment

During the first century of mining in Colorado, environmental concerns and employee health were secondary to production. After about 1960, however, a growing awareness of problems such as pollution and contamination led to new regulations and cleanup efforts that affected all aspects of the Colorado mining industry. In the case of molybdenum, environmental regulations shaped and sometimes prevented new mining efforts. In the 1960s, for example, corporate owner AMAX prepared for the start of open-pit surface mining at Climax by acquiring much of the upper Tenmile valley as a site for gigantic tailings ponds to contain the waste. Once that was done, open-pit surface mining began in the 1970s in an attempt to counter increasing competition from newer, cheaper foreign mines.

Meanwhile, AMAX also acquired a small molybdenum orebody west of Empire and started exploration there, eventually discovering a giant orebody some 4,000 feet beneath the surface. Because the orebody was deep under a narrow valley near the headwaters of an important Denver water source, the company worked with environmental groups to plan an operation that kept surface facilities to a minimum. The company also constructed its mill and tailing-disposal site fifteen miles away, on the western side of the Continental Divide. Development of the Henderson Mine and mill took nearly a decade and cost about $500 million, making it the largest privately financed project in Colorado history to that point. Production started in 1976, and Henderson soon matched Climax, with each mine producing roughly one-quarter of world supply.

With molybdenum booming in the late 1970s, AMAX even made plans for a third large mine at Mt. Emmons near Crested Butte. However, the project faced strong opposition from preservationists, tourists, and environmentalists, then foundered when the world molybdenum market collapsed in the early 1980s. That collapse led AMAX to suspend production at both Climax and Henderson, which had strong negative impacts on local communities that relied on the mines for employment. Henderson resumed limited production in 1984, but Climax remained mothballed for most of the next two decades.

Uranium brought a different set of problems. As early as 1956, officials had documented an epidemic of small-cell lung cancer among uranium miners in western Colorado, particularly those who smoked and worked in poorly ventilated mines. But no regulations were put in place until the 1960s, and not until 1990 did Congress pass the Radiation Exposure Compensation Act to assist families with health care and other expenses.

Meanwhile, uranium production in Colorado dwindled in the 1970s and collapsed after a meltdown at the Three Mile Island Nuclear Generating Station in Pennsylvania in 1979. The Uravan Mill shut down in 1984, and Colorado’s last uranium mining company closed in 1990. The state of Colorado sued Union Carbide in the wake of the Three Mile Island accident, leading to a Superfund cleanup that condemned the entire town of Uravan in 1986 and painstakingly destroyed it over the next two decades at the cost of some $130 million. Everything radioactive in the town was buried in a nearby mesa, and the abandoned site now belongs to the Department of Energy. Former residents and workers hold annual reunions at a local ballpark that was spared. Colorado also has about a dozen former uranium disposal and processing sites that are managed under the Uranium Mill Tailings Radiation Control Act of 1978.

More broadly, mining and smelting resulted in contaminated soil and water wherever those activities occurred. Serious cleanup efforts began after Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act, commonly known as the Superfund law, in 1980. Over the next few decades, more than a dozen Colorado mining and smelting areas were listed as Superfund sites, including Uravan and a uranium mill in Fremont County, as well as more conventional mining and smelting districts in Boulder, Chaffee, Clear Creek, Eagle, Gunnison, Lake, Mineral, Pitkin, and San Juan Counties. Denver alone has several Superfund designations resulting from smelting and radium-ore processing. Some sites were fully remediated in the 1990s and early 2000s, but long-term cleanup efforts continue in many areas.

Today

Today molybdenum is the primary metal still mined in Colorado, and the state remains the nation’s top molybdenum producer. When world molybdenum prices rebounded in the early 2000s, corporate owner Freeport-McMoRan increased production at Henderson and revived Climax—historically the state’s largest and most important mine—in 2012. By that time, Henderson had yielded roughly 1 billion pounds of molybdenum, whereas Climax had produced around 2 billion pounds over its life. At current production levels, both mines are expected to last until the late 2030s, when remediation efforts will begin.