I have seen this posted other places, but since I actually did this myself, I'll post about it.
The Bingham Canyon mine (Kennecott Copper) is free to the public until July 25th. Normally it's $5 per car, so it's a great deal. They have a little visitor's center with a short 10 minute video you can watch (and learn) about what goes on at the mine, and how it all works. Plus it was pretty amazing to be able to look down into a 3/4 of a mile hole in the ground!
For more info, go HERE.