This is an old, but cautionary tale. News From Indian Country, Jan. 2012, at 6-10, reports in detail on the problems of cyanide heap leach mining near the Fort Belknap Reservation.
The Zortman and Landusky mines began using the cyanide process and Montana, the United States, and the Tribe ultimately sued the operator Pegasus Gold in 1994. canadian company declared bankruptcy. The suit was settled and Pegasus agreed to pay some fines and guarantee $800,000 a year for water treatment.
The company later went bankrupt, the price of gold dropped, and state and federal dollars are being spent to clean up the mess.