There are likely a lot of geologists that would recognize the above pictures as the Berkeley Pit in Butte, Montana. My first visit to the pit was shortly after mining in the pit had ceased in the early 1980s. We made a visit to Butte, not for the geology but in order for an associate to get his boots repaired after and before looking at other geology sites. Since that time the lake in the pit has increased in size substantially.
Berkeley Pit is the dark lake in the center
Active open pit mining is located on the upper right and
the tailings pond for the active mine is on the upper left
An initial reaction of revulsion to huge open pit mines filled with toxic waters is understandable. But most geologists and miners will point out that society demanded that we dig this big hole in the ground. Indeed, the very fact that you are reading this blog means that you are a consumer of the resources that placed a huge demand for getting copper out of the ground for use as an electric conductor as well as a huge variety of other uses.
Initially all the mining in Butte was done via multiple underground shafts mining along rich veins of copper. Butte was not a boom and bust mining town. There were dozens of rich copper ore veins and underground mining lasted for many decades and generated great wealth not only in Butte but in the United States. This rich mining history built a city that is unique for western U.S. cities, and the city now has a very large historic district that is well worth seeing. And I will add that down town Butte is in much better shape today than when I first visited in the early 1980s.
Open pit mining began in the 1950s as a result of the rich vein mining coming to an end, the high prices of copper (societal demand), and more efficient earth moving and ore processing. But there were serious trade offs to open pit mining. For one, the pit not only consumed a huge volume of rock but took out entire neighborhoods in the city. On the positive side, the pit was good for the local economy. Pit mining was also safer than underground mining at the time. Miners routinely died in the underground mines in Butte. There is a heart wrenching memorial to one particularly bad mining accident on the hill north of town.
In the 1950s when open pit mining began, societal views of and understanding of environmental damage was much different than today. Groundwater was pumped before entering the pit, but when mining ceased the pit began filling with water. The oxygen rich water reacts with the rocks creating sulfuric acid and leaching metals including arsenic. The Berkeley Pit and a variety of mine related sites has made Butte the largest and most expensive Superfund cleanup site in the United States.
The current very high prices for copper is good news for Butte. Mining is continuing at a pit immediately to the east. And the high copper prices are good for the environment.With the high copper prices the cost of processing the toxic water has been substantially reduced because the water itself is full of copper. One report states that 400,000 pounds of copper are extracted from the pit water every month.
Although the pit lake is very toxic, the lake in the pit is not dead. Over 167 species of bacteria and fungi have been identified. Figuring out how these critters live and function is ongoing and in the end the pit may save lives as chemicals extracted from some of the bacteria show great promise as cancer fighting agents http://mtstandard.
As distasteful as the pit may be, keep in mind that your using the products from the pit and perhaps a loved one or you yourself may be saved by the chemicals identified in the lake ecosystem. Our side trip to Butte was well worth the time.
Find out lots more at http://www.pitwatch.org.