Located about two miles west of Nederland in western Boulder County, the Cardinal Mill processed gold, silver, and tungsten ore from its parent mine, the Boulder County Tunnel, as well as other local mines between 1902 and 1942. The Cardinal Mill was an essential part of the area’s tungsten boom in the early twentieth century and is a rare example of an intact mill from that period. Boulder County acquired the mill in 2003 and performed multiple rehabilitations to the building and grounds from 2005 to 2010. In 2011 the Cardinal Mill was listed in the National Register of Historic Places.
Mining the Boulder County Vein
Boulder County was the site of some of the earliest mining camps in the Colorado Gold Rush of 1858–59. As prospectors scoured the mountains for more minerals in the ensuing decades, the town of Caribou was established near prospector Samuel Conger’s silver strike west of Boulder in 1870. Conger had found a large gold and silver vein on the east slope of Boulder County Hill, which he named the Boulder County Vein. He and another prospector drove mine shafts into the vein, and an influx of miners set up a nearby camp that was organized as the town of Cardinal in 1872.
In 1875–76 Conger and his investors began work on a seven-by-seven-foot tunnel underneath the vein. This would allow the mine’s water table to drain, exposing more ore, and would also allow ore to be shipped out underneath the vein instead of hauled to the top of a shaft. However, the tunnel was more expensive than anticipated, and several groups of investors ran out of money before the tunnel finally reached the vein in 1905 under the auspices of engineer Chauncey F. Lake.
Milling Ore at the Cardinal
As part of his larger development plan for the Boulder County Mine, Lake had the Cardinal Mill built near the mouth of the Boulder County Tunnel in 1901–2. In its first several years of operation the mill generated more than $100,000 in gold and silver.
The Cardinal Mill was built on the southwest slope of Boulder County Hill in four descending levels, beginning with the ore-receiving room at the top. Although the building’s staircase of corrugated iron roofs gives the impression that each section is separate, the interior is open, with machinery for different stages of ore processing occupying different levels. The mill’s equipment and processing methods were upgraded many times during its forty-year operating period, but in general ore taken to the mill went through four steps: it was received, crushed, further reduced to a fine sand or slurry, and then chemically treated to separate metals from surrounding material.
Each of these stages generally occurred on its own level, with raw ore received at the first level, crushed on the second, pulverized on the third, and concentrated and shipped out on the fourth. Lake initially used mercury and cyanide to separate gold and silver from the ore slurry; future owners would improve these methods as technology allowed.
Discovery of Tungsten
When Boulder County miners came across a heavy black ore in the 1870s, they quickly tossed it aside, believing it to be worthless. In fact, the ore contained tungsten, a steel-strengthening element that would later be in worldwide demand for its use in light bulbs, ordnance and ammunition, high-speed manufacturing tools, and many other products.
The town of Cardinal may have dried up by the turn of the century, but Conger’s luck had not. Around 1900 he began identifying tungsten ore in his mines. At the time, the metal was just being experimented with as a steel alloy, but it did not take long for metallurgists to discover an efficient method for alloying tungsten. Soon the Nederland area became one of the world’s only known sources for large amounts of tungsten. However, buyers in Europe and the East Coast would only pay high prices for tungsten if it was concentrated—separated from its rocky shell—and since tungsten was a new commodity, no one had yet developed an effective concentration method.
Lake figured it out. In 1903 he purchased Conger’s tungsten mine and began concentrating the ore at the Cardinal Mill. As it turned out, the mill’s equipment at the time was just as well—and perhaps better—suited to process tungsten ore as it was gold and silver ore. As one of the nation’s first mills outfitted to do so, the Cardinal Mill was soon concentrating tungsten ore from all over Boulder County. The new metal was so profitable that Lake and his main investor, Pittsburgh oil man T. F. Barnsdall, stopped all development at the Boulder County Tunnel and organized the Cardinal Company as an ore-buying outfit in 1906.
Decline, Upgrades, and Revival
In 1908 Lake and Barnsdall merged the Cardinal Company with the Stein-Boericke Company, a leading tungsten producer. That company was soon acquired by the Primos Chemical Company, one of the nation’s largest tungsten consumers. Lake managed the Cardinal Mill from 1909 to 1910, when he opened a larger tungsten mill in Lakewood. With the Cardinal Mill no longer the area’s primary concentration facility, Lake attempted further development of the Boulder County Tunnel in 1909 and revamped the mill’s concentration process in 1911 in an attempt to process the tunnel’s more complex gold and silver ore. But he was not successful, and overall the mill did little work between 1910 and 1915. Meanwhile, large tungsten deposits began to be mined in California, bringing an end to Boulder County’s short reign as tungsten capital of the United States.
In 1919 tungsten operator John G. Clark leased the Boulder County Tunnel and the Cardinal Mill. Clark replaced the mill’s steam engine with electric motors and gave the mill’s ore reduction and concentration equipment a much-needed upgrade. First, he added a rod mill to the reduction stage. The rod mill was a large rotating cylinder filled with steel rods that tumbled into each other and ground the ore into an even finer slurry. From there, the slurry was dumped into new flotation mills—vats containing a mix of water and chemicals that separated metal in the slurry and allowed it to rise to the surface in a froth that was then skimmed off by rotating paddles. The skimmed-off metals went down a flume into a collection vat, where workers rinsed and dried the concentrates before sacking them for transport to smelters.
In addition, Clark added more sophisticated vibration tables to collect waste material left at the bottom of the flotation mills, which still held a small amount of recoverable metal. The leftover slurry was pumped out onto the vibrating tables, which were outfitted with metal riffles. The vibration caused the heavier metal in the slurry to sink into the riffles; a water current washed the waste away while the metal content was channeled into collection troughs that took it back to the same vat that received metal concentrates from the flotation mills.
With this new concentration and collection process, the mill could now handle the more complex ore from the Boulder County Tunnel. Clark oversaw operations at the mill for a year before subleasing the property; when that tenant ran out of money, Clark again took over the Cardinal Mill and prepared the property for a new lease.
Continued Operation and Closure
In 1924 the Cardinal Mill changed hands again, with John Bergren and F. M. Holmes leasing the entire Boulder County property as the Fairview Mining Company. In 1927, a year after profits began to decline due to insufficient metal recovery, the company again revamped the mill’s concentration process, upgrading its flotation equipment and installing more vibrating tables to collect metal from slurry.
The Fairview Company’s improvements allowed the mill to process a daily ore load of 110 tons in 1928, but near the end of that year the company ran out of usable ore and closed. Despite multiple attempts by Fairview and other outfits to revive the mill, the Cardinal remained relatively unprofitable during the 1930s.
The last owner to operate the Cardinal Mill was the Donora Mining Company in 1941–42. Under the leadership of Alvin Rohn, the company had the mill processing fifty tons of ore per day in 1942, but optimism about the mill’s future was cut short at the end of the year, when the federal government suspended gold mining for the duration of World War II. The Cardinal Mill never again operated in a meaningful capacity.
The Cardinal Mill lay dormant for decades after its closure. In the late 1990s, local real estate investor Alexandra Armitage bought the historic town site of Cardinal with the intention of rehabilitating its nineteenth-century structures. Armitage’s project drew attention to the area’s historic structures, and in 2003 she sold the mill to Boulder County.
By the time Boulder County acquired the Cardinal Mill, the entire building had begun a slow slide down the hill toward Coon Track Creek. Part of a retaining wall for the mill’s waste pond had collapsed, allowing waste rock to pile against the side of the mill. Not only did this threaten to collapse the mill, but the Colorado Department of Public Health and Environment also found that metals from the waste pond were leaching into the creek. In 2005, with help from the State Historical Fund (SHF), Boulder County Parks and Open Space began shoring up the retaining wall using the same materials as the original wall. Another retaining wall on the east side of the mill was repaired in 2008.
Work to repair the mill itself also began in 2005. Between 2005 and 2010 Boulder County, along with Historic Boulder, Inc., obtained a total of more than $600,000 in SHF grants for renovations to the Cardinal Mill, including roof and wall repairs, window replacements, and structural support.
Inside, the Cardinal Mill’s current condition reflects the numerous, often hurried developments of its many previous owners. Machinery and wooden support structures were haphazardly fastened to existing structures or the building’s frame, with little or no evidence of planning. Outside, the mill retains its characteristic four-leveled roof, flanked by restored retaining walls. Located off County Road 128 (Caribou Road), the Cardinal Mill is currently closed to the public for safety reasons; however, the county hopes to use the building for historic tourism in the future.