Located two miles northeast of Silverton, the Shenandoah-Dives Mill (also known as the Mayflower Mill) was constructed in 1929 and became the longest-running mill in the San Juan Mountains. Operating most years from 1930 to 1991, the mill processed a total of nearly 10 million tons of rock and produced roughly 1.9 million ounces of gold, 30 million ounces of silver, and 1 million tons of base metals. Designated a National Historic Landmark in 2000, the mill is now owned by the San Juan County Historical Society, which maintains the site and offers tours in the summer.
Building the Mill
In 1925 a syndicate from Kansas City, Missouri, bought mining claims covering 316 acres in the San Juan Mountains near Silverton and started the Shenandoah-Dives Mining Company. With mining engineer Charles A. Chase serving as general manager, the company developed its holdings and started to plan a new mill to process its ore in the valley below the mines. In 1928 Chase presented a proposal to the syndicate outlining plans for a tunnel, tramway, and mill. The syndicate accepted the plan, and construction began in June 1929.
Chase turned to colleagues in Denver to help him with the design and construction of the flotation mill—a mill that concentrates metals through a flotation process—which he planned to build at the base of the mountain. He hired a former colleague from the Colorado School of Mines, Arthur J. Weinig, as consulting metallurgist and engineer. The Denver-based company of Stearns-Roger Engineering designed the structure that was to become the Shenandoah-Dives Mill.
Laborers hitched the base of the four-story building to the side of the mountain. Then they poured the concrete floor of the mill. The heavy equipment for the mill arrived by train to be positioned as Weinig directed. Men and machines hoisted heavy boilers, synchronous motors, and two-ton ball mills into place. The mill building itself arrived as a pre-numbered kit. Carpenters pieced it together like a puzzle around the innards of the mill, which sat at the base of Arrastra Gulch looking up toward the mine.
Locals have always referred to the mill as the “Mayflower Mill” after the nearby Mayflower Mine portal. An aerial tramway connected the Mayflower Mine to the Shenandoah-Dives Mill. Carrying men as well as ore and equipment, the aerial tram was the lifeblood of the mining operation.
By 1930 the Shenandoah-Dives Mining Company had invested $1.25 million in its Silverton operations. The syndicate’s initial reason for investing in the Shenandoah-Dives Mine was for precious metals—gold and silver—but base metals fast became the company’s economic mainstay. During the 1930s the Shenandoah-Dives Mining Company’s production of copper, lead, and zinc helped meet the needs of America’s manufacturing companies. From 1930 to 1932 the mill processed more than 450,000 tons of ore. Shenandoah-Dives represented the largest single industrial payroll in the Four Corners region.
During the Depression, Chase gambled that the Shenandoah-Dives Mining Company’s production of base metals, such as lead and zinc, would carry the cost of the operations, with additional profit from gold and silver. To ensure the success of the Shenandoah-Dives operation, Chase built and ran the Silverton complex with the newest, most efficient mining and milling processes available. Equipment upgrades over time enabled the mill to separate five products from the ore: gold, silver, copper, lead, and zinc.
The Shenandoah-Dives Mill responded to the increased environmental concerns of the early twentieth century. The operation was the first in the region to use tailing ponds. Common practice was simply to slurry the tailings into available waterways, despite the dangers to the water supply and fish population. Chase consulted with J. T. Shimmin, who had devised a method of creating “ponds” of tailings at mills in Butte, Montana.
After visiting Shimmin’s site in Montana, Chase returned and adapted Shimmin’s design to a triangular chunk of land just south of the Shenandoah-Dives Mill where tailings were deposited. Water was decanted off the surface, filtered, and returned to the mill. Much of the water either evaporated or percolated through the tailings and into the substructure. The ponds’ location kept the runoff from percolating into the Animas River just east of the mill. After a trial period—with a few mishaps due to freeze and thaw—the tailing ponds of the Shenandoah-Dives Mill took shape in 1935.
World War II and After
World War II ushered in a period of artificially inflated prices for essential resources and revived the mining industry across the nation, including the Shenandoah-Dives operations. Chase convinced the War Department that the Shenandoah-Dives Mine’s base metal production was essential to national security, allowing the Shenandoah-Dives Mill to stay open and supply America’s needs through World War II and the Korean War.
When the wars ended, the demand for metals stopped. Stockpiled metals met the needs of manufacturers who now turned from munitions production to household goods. While other industries flourished, the gold and base metal industry languished.
In 1953, after twenty-five years of mining and milling in Silverton, the Shenandoah-Dives Mining Company shut down its operations. In its history, the mill had processed four million tons of Shenandoah-Dives Mining Company ore and 186,000 tons of custom ore from surrounding smaller enterprises. In total, the Shenandoah-Dives Mill had processed 11 percent of all the gold, silver, copper, lead, and zinc in Colorado. When the mill closed in 1953, the total assayed value of the Shenandoah-Dives Mill production was $32 million.
With the company’s demise, smaller Silverton companies, which relied on the Shenandoah-Dives Mill to buy their ore, were forced out of business. In fact, the years 1954 to 1959 were an era of mine closures throughout the industry. It was not only the end of an era for Charles Chase and Shenandoah-Dives, but also for underground mines and small flotation mills in general. When the mining industry rebounded in the 1960s, open-pit mines and large milling operations ruled the industry.
The syndicate’s firing of Chase and closure of the Shenandoah-Dives mine and mill did not signal the permanent end of operations. Between 1953 and 1957 the mill operated intermittently as the company underwent a series of ownership changes. In 1957 the mill reopened on a more permanent basis. After several mergers and sales, it became part of the Standard Metals Corporation. In 1960 the Shenandoah-Dives Mine closed, but the mill continued to operate, processing ore from area mines.
In 1985, Standard Metals sold its Shenandoah-Dives holdings to the Sunnyside Gold Corporation, a subsidiary of the Echo Bay Mining Company of Edmonton, Canada. Sunnyside and associated companies participated in two joint ventures using the mine and mill. By 1990 Sunnyside Gold was the sole owner. In 1992 Sunnyside announced permanent closure of the mine and mill because of declining zinc prices and a lack of gold reserves.
After the final closure of the Shenandoah-Dives mines and mill, Silverton’s population declined by nearly half as miners and their families moved on. Like other former mining towns in the Rocky Mountain West, Silverton’s economy now relies on government activities and tourism.
Sunnyside Gold donated the flotation mill and affiliated lands to the San Juan County Historical Society. By 1996 surface reclamation of the tailing ponds and mine site was substantially complete. Through the work of local preservationists and the historical society, the mill reopened in 1997 as a museum. In 2000 the mill was designated a National Historic Landmark.
The San Juan County Historical Society has received more than $500,000 in grants from the State Historical Fund, the National Trust for Historic Preservation, and other organizations for the stabilization and restoration of the Shenandoah-Dives Mill. The historical society’s goal is to rehabilitate each building within the large mill complex. In addition, in 2010 the historical society received a State Historical Fund Special Initiatives grant to build hydroelectric power into the mill to offset the mill’s large electricity bill and improve the supply of drinking water in the area.
*Adapted from Dawn Bunyak, “Shenandoah-Dives Mining Company: A Twentieth-Century Boom and Bust,” Colorado Heritage (Spring 2003): 35–46.