Gold expresses itself wherever water wells up out of the earth, and that occurs where there are mountains and rivers. The Blackfoot River in western Montana is one of these rivers. Made famous by the book and movie “A River Runs Through It,” the river that people saw in the movie was actually the Gallatin, since logging and mining have ruined much of the Blackfoot. Now the river faces what may be its biggest threat. Despite some opposition, a giant gold mine is rising along its banks. Steve Curwood spoke with Richard Manning, who lived near the Blackfoot for many years, and has written a book called “One Round River: The Curse of Gold and the Fight for the Big Blackfoot.”