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Gunnison Mill
Location: The Gunnison uranium mill site is located just southwest of the City of Gunnison in Gunnison County, Colorado.
Background: In 1954-1955, uranium deposits were discovered in the Cochetopa, Tallahassee Creek, and Marshall Pass uranium districts in the Southern Rocky Mountains of central Colorado. Development of the deposits soon followed. In November 1956, the Atomic Energy Commission (AEC) signed a contract with the Gunnison Mining Company (GMC) for a small uranium mill at Gunnison, Colorado. The mill was built on a 62-acre tract just south of Gunnison, and its first delivery under GMC’s only contract was made in February 1958. In late 1961, GMC’s assets were acquired by Kermac Nuclear Fuels Corporation (KNF). The mill continued to operate under KNF until April 1962, when it was closed down. Originally designed for a throughput capacity of 200 tons of ore per day (TPD), the mill was operated over its life at an average of 350 TPD, due to the lower than anticipated grade of ore received. Ore deliveries in 1958 averaged 0.24 percent U3O8, but the grade declined to about 0.12 percent during 1960-1962. The mill feed consisted mainly of uraninite in silicified and brecciated elastic rocks and came mainly from company mines in the Cochetopa district, but a small amount of ore was purchased from independent miners. From January 1958 to April 1962, the mill processed about 540,400 tons of ore that averaged 0.15 percent U3O8 and recovered 1.45 million pounds U3O8 in concentrate. All concentrate production was sold to the AEC. Uranium was leached from the ground ore using sulfuric acid and sodium chlorate as the oxidant. A four-stage classifier-thickner circuit then separated the pregnant solution from the washed solids, which were sent to tailings. Uranium was concentrated from the pregnant solution using solvent extraction. Sodium carbonate solution was then used to strip the uranium from the solvent. This alkaline stripping formed an iron precipitate that was filtered from the solution and saved as an iron cake. From the clarified solution, uranium was precipitated and filtered. The final yellow cake product was dried and packed for shipment to the AEC’s Grand Junction, Colorado facility. After the mill was closed, the 39-acre, partially filled, tailings impoundment pond was reclaimed in accordance with plans approved by the Colorado Department of Health: the pond area was contoured, covered with soil material from a local gravel pit, and was planted with a mixture of grasses. A narrow, 3.5-acre parcel of the mill property was deeded to Gunnison County in 1966 for use in expanding the local airport facility. After 1964, several different owners held the remaining mill site property. In 1990, the mill site was acquired by the State of Colorado, which later assigned site ownership to Gunnison County.
Background: In 1954-1955, uranium deposits were discovered in the Cochetopa, Tallahassee Creek, and Marshall Pass uranium districts in the Southern Rocky Mountains of central Colorado. Development of the deposits soon followed. In November 1956, the Atomic Energy Commission (AEC) signed a contract with the Gunnison Mining Company (GMC) for a small uranium mill at Gunnison, Colorado. The mill was built on a 62-acre tract just south of Gunnison, and its first delivery under GMC’s only contract was made in February 1958. In late 1961, GMC’s assets were acquired by Kermac Nuclear Fuels Corporation (KNF). The mill continued to operate under KNF until April 1962, when it was closed down. Originally designed for a throughput capacity of 200 tons of ore per day (TPD), the mill was operated over its life at an average of 350 TPD, due to the lower than anticipated grade of ore received. Ore deliveries in 1958 averaged 0.24 percent U3O8, but the grade declined to about 0.12 percent during 1960-1962. The mill feed consisted mainly of uraninite in silicified and brecciated elastic rocks and came mainly from company mines in the Cochetopa district, but a small amount of ore was purchased from independent miners. From January 1958 to April 1962, the mill processed about 540,400 tons of ore that averaged 0.15 percent U3O8 and recovered 1.45 million pounds U3O8 in concentrate. All concentrate production was sold to the AEC. Uranium was leached from the ground ore using sulfuric acid and sodium chlorate as the oxidant. A four-stage classifier-thickner circuit then separated the pregnant solution from the washed solids, which were sent to tailings. Uranium was concentrated from the pregnant solution using solvent extraction. Sodium carbonate solution was then used to strip the uranium from the solvent. This alkaline stripping formed an iron precipitate that was filtered from the solution and saved as an iron cake. From the clarified solution, uranium was precipitated and filtered. The final yellow cake product was dried and packed for shipment to the AEC’s Grand Junction, Colorado facility. After the mill was closed, the 39-acre, partially filled, tailings impoundment pond was reclaimed in accordance with plans approved by the Colorado Department of Health: the pond area was contoured, covered with soil material from a local gravel pit, and was planted with a mixture of grasses. A narrow, 3.5-acre parcel of the mill property was deeded to Gunnison County in 1966 for use in expanding the local airport facility. After 1964, several different owners held the remaining mill site property. In 1990, the mill site was acquired by the State of Colorado, which later assigned site ownership to Gunnison County.
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