April 1999

Chemistry Corner
PitWatch Issue Volume 4, Number 1

The equation below shows the main chemical reaction that takes place during the copper precipitation process:

Fe + CuSO4 = FeSO4 + Cu

Butte's Memory Book tells the story of Jim Ledford, a miner who lived in a log cabin below the famed Anaconda Mine.

Alongside his cabin was an old dump containing scrap iron and tin cans. Mine water ran downhill through the dump, and Ledford noticed a heavy sludge formation. Out of curiosity, he had the sludge assayed and learned that it was 98-percent-pure copper.

Legend has it that Ledford told no one about his discovery. Instead, he quietly secured a one-year contract to handle the Anaconda mine water. He set up tanks, filled them with scrap metal, and ran the water through them. The undated account said his efforts earned him $90,000 that first year.

And it said his contract was not renewed.

A professional paper from a 1913 Butte mining conference tells a slightly different story. It states that in 1890 a William Ledford obtained a contract to handle water from the St. Lawrence Mine. The story ends the same, however: Once the Anaconda Co. realized the value of mine water, it built its own "copper tanks" as they were called, and copper precipitation using scrap iron became standard operating procedure.

Thanks to Al Hooper for loaning his copy of the 1913 mining conference proceedings.

Using a method dating back to medieval Europe, Montana Resources (MR) has begun to mine copper from the rich mineral waters of the Berkeley Pit. In early March, MR started pumping out 5,000 gallons of water per minute. That volume will double once construction of a second pump/pipe system is complete.

The Pit water is piped to the company's precipitation plant, built in the 1960s next to a similar one from decades before. The water flows into concrete cells filled with scrap iron, and the chemistry magic begins. Simply put, the iron in the cells and the copper in the water trade places. The water exits with a higher iron content, and the copper precipitates, or falls out of solution, clinging to the remaining iron.

The chemical reaction doesn't take long. Water stays in contact with the iron for only about an hour, and then it flows back into the Pit through the old Horseshoe Bend channel. MR officials say that this constant circulation process should not affect the water level of the Pit, nor should the change in water chemistry have an effect on eventual water treatment operations.

Once a week, crews drain each cell to recover the copper. A front-loader scoops up the copper/scrap iron mixture and transports it to a vibrating screen. Water sprayed from high-pressure hoses knocks the copper through the screen into a tank below. Remaining iron goes back to a cell for reuse. The copper slurry, now about 80 percent water, is trucked to the Concentrator and put through a filter press which cuts the water content to about 20 percent.

This 'elemental copper' is particularly valuable to MR because, unlike the copper obtained from the Continental Pit, it does not require smelting or refining. By pumping water from the Berkeley, MR hopes to recover at least 4 million pounds of elemental copper each year for the next four years and possibly for up to nine years.

MR officials say this Pit-water-pumping operation would not have been economical had the precipitation plant not been in place. And they say both the costs and benefits of this project are minuscule compared to the future costs of treating the Berkeley Pit water.

The company also started routing copper-rich Horseshoe Bend water through the precipitation plant about two years ago. This water has yielded around 1.2 million pounds of copper each year, the sale of which has helped to offset water treatment costs. Once through the precipitation plant, Horseshoe Bend water is mixed with lime and pumped up to the Yankee Doodle Tailings Pond.

Note: MR and ARCO are responsible for the future construction of a water pumping and treating facility that will maintain the water level in the whole Berkeley Pit/East Camp system at an elevation below 5,410 feet. The plant must be operational four years before the water is expected to approach 5,410.

Monitoring Well Update
PitWatch Issue Volume 4, Number 1

Replacement monitoring Well I is not yet installed. The last PitWatch reported that crews expected to finish installation in November, but soon thereafter the well's plastic casing collapsed at about 621 feet underground. Because plastic shatters easily in cold weather, further work was postponed until spring.

Montana Resources, ARCO, and the regulatory agencies are now deciding whether they can salvage the current well or need to start over in a new location. A decision should be made by the end of April 1999. We'll continue to provide updates on this and other monitoring well developments in future issues.

October 1999

Pit Facts Comparison
PitWatch Issue Volume 4, Number 2

Compare Pit elevations to those of…
the Belmont Senior Center at 5,605 feet above sea level;
East Middle School at 5,517 feet;
the Butte Airport at 5,525 feet;
the County Courthouse at 5,755 feet.

Compare the depth of Pit water to the height of…
the Anaconda smelter stack at 585 feet;
Seattle's Space Needle at 605 feet;
Timber Butte which rises 834 feet above the Municipal Golf Course.

Compare the volume of water in the Pit to…
5 ½ Silver Lakes;
83 Basin Creek Reservoirs;
78,000 Stodden Park pools.

Pit Facts At A Glance
PitWatch Issue Volume 4, Number 2

Current Water Level: 5,175 feet above sea level
Average Rate of Rise: About 1 foot per month
Critical Water Level: 5,410 feet above sea level
Rim of Pit at Lowest Point: 5,509 feet above sea level
Number of years before water hits Critical Level: (approximate) 21 years
Depth of Water: 702 feet (plus about 200 feet of sediment at the bottom)
Volume of Water: About 30 billion gallons