I think most of the piles will be unprocessed ore, rather than tailings. If you go to the report from the Idaho Geological Survey (which I've linked to a couple of times), you will see that most of the piles are around mining sites- unprocessed ore. There are fewer mill sites, where tailings would be found. In fact, the report states:

“The only mill site in the area with a significant amount of tailings is at the Dewey Mine.” p 19