Kenwyn George was provided a tour of the tailings impoundments, water handling facilities and water treatment by Tavis D. Rogers, P.E., Senior engineer, of Climax Molybdenum on October 23, 2008.

Brief history of the mine

The mineral body was found by a prospector named Charles Senter in 1879. It is 13 miles from Leadville and at an elevation of 13, 318 feet above sea level. Senter did not know what the mineral was. It was identified as Molybdenum in 1895 and initially mined from 1915-1919, then 1924-1983. In the 1970’s there were 3000 people at the mine. When it shut down in 1985, half the population of Leadville left town. The mine was initially an underground mine (there is a 1000’ deep shaft used to dewater the mine); it is now an open pit mine.

The molybdenum is in the form of small veins in a stockwork in altered quartz monzonite porphyry. Byproducts include tin from casserite, tungsten from hubnerite and pyrite.

The Climax Mine has been in a care and maintenance mode since the last production run in 1997. A new mill is under construction and due to commence operation in 2010. Climax has an excellent compliance record with no environmental incidents for many years. Facts from the tour:

They get approximately 270” of snow a year.

There are 4 tailings dams and three tailings ponds. The #3 dam was built in the 1950’s, the #5 dam in 1971/1972. Tailing will be deposited on #3 Dam for the first several years of production and then deposition on #5 Dam for life of mine.

The #3 dam toe drains have experienced minor failures, creating an area with small sink holes. These are presently being excavated and replaced. The dam was made of tailings and was re-graded to a nominal 2.75:1 slope, capped with approximately 2 feet of cover and re-vegetated in 1997.

Reclamation is underway in a variety of locations. The Robinson Lake was partially drained and metals containing sediments being removed to increase process water storage and reclaim areas early. Peat and clean topsoil from beneath the sediments are being excavated from below the sludge and used as reclamation material on the #1 Dam face and Robinson Tailing Pond surface. Approximately 670,000cy of sediments, peat moss, topsoil, and subsoils is anticipated to be removed from the reservoir in 2008.

The tailings are being reclaimed by covering with approximately 2 feet of cover followed by application of biosolids (composted municipal wastewater treatment plant sludge and wood chips), scarifying the surface, and then seeded with the Climax native seed mix. There are a number of areas where acid generating rock was used for capping that require additional applications of lime at rates of up to 30 tons/acre, by application of biosolids, scarification, and seeding. The Robinson Tailing Pond facility is approximately 350 acres, most of which is now reclaimed, and there is a permitted 65 acre water pool on the tailing pond surface which may or may not remain for the long term. Over 900 trees salvaged from areas that were being disturbed by other projects have been planted on the reclaimed areas.

The #4 dam was historically the molybdenum oxide tailing pond. Approximately 1.3 MT of molybdenum oxide tailing was removed from the tailing pond in 1996 and 1997 and deposited in Tenmile Tailing Pond off of #2 Dam. This tailing facility is fully reclaimed as Eagle Park Reservoir and is used as water storage for local ski areas and municipalities. The stored water meets or exceeds all stream release and drinking water standards.

There are approximately 45 miles of interceptor ditches that divert clean water from around affected areas. The impacted waters requiring treatment are from the tailing dams, open pit area and underground workings. The industrial water treatment system is a two-stage pH adjustment and precipitation of metals sludge on the tailing ponds. The treatment process is accomplished by the addition of lime with the first stage through the Sludge Densification Plant and on Tenmile Tailing Pond targeting a pH of 6.5 to 7.0 to drop out iron, aluminum and co-precipitation of molybdenum with iron. The second stage treatment is on Mayflower Tailing Pond is to a target pH of 9.8 to precipitate zinc and manganese. The pH in the decant from the Mayflower pond has a pH around 8.6 to 8.9. Sulfuric acid is added to the effluent before it discharges to Tenmile creek with a target pH of 7.8.

Drainage from historic mines is also treated by Climax . Pollutants in the runoff from these areas are primarily iron and zinc. Climax has removed tailing and reclaimed these historic workings and anticipates improved water quality from these areas as the reclamation progresses.


Pit and ore body

Diorama in the Leadville mining Hall of Fame

Tailings pond used for treatment

Valley filled with tailings

Effluent to Tenmile Creek

Tailings pipes with drops to prevent solids from settling out

Climax also had a molybdenum mine near Berthoud Pass (the Urad mine) that has been reclaimed. See