Note: This article is a sidebar to this issue’s feature story.
If the McDonald gold mine is built as currently planned, it will resemble a city of eight square miles. It will be thirsty. Each day it will use an average 2.5 million gallons of water, equivalent to 420,000 toilets flushing. It will also be noisy. Blowing up the forested buttes that cover the ore will require 27 million pounds of ammonium nitrate (the Oklahoma City bombers used 4,000 pounds) plus 220,000 gallons of fuel oil.
The explosions will eventually create a pit over a mile wide, nearly a mile long and 1,200 feet deep, large enough to swallow 100 Sphinxes. For the first three years, the pit will be kept dry by pumping out 15.8 million gallons of groundwater daily; 3 million gallons more than the city of Great Falls, Mont., uses in a day. The pit will never be filled in.
Since the ore is low-grade, 50 tons of it will be exhumed from the pit for every ounce of gold. The ore will be dumped onto an area as large as 342 city blocks. This pile will be sprayed with sodium cyanide to leach out the gold it contains. Afterward, giant trucks will move the waste rock to another pile that covers 350 city blocks and reaches 600 feet high. This city will reach to within a quarter mile of the Blackfoot River.
To supply this city, each year 788 truckloads of diesel fuel, 386 truckloads of ammonium nitrate and 236 truckloads of sodium cyanide will navigate a two-lane mountain road past the town of Lincoln.
After 10 to 20 years, the city will shut down, leaving the open pit, the denuded slopes, and the ground a pale bone color, much like an X-ray of a mountain.
(Figures courtesy the Clark Fork Pend Orielle Coalition and the Montana Environmental Information Center.)
This article appeared in the print edition of the magazine with the headline A gold mine is a city until the ore runs out.
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