Extractive industries are booming.Miners find it worthwhile to dig for copper in Butte, Montana, even though the operators say it is the worst-grade ore in the world.

• 开采业日趋繁荣，尽管矿主认为这里矿石的品质堪称世界最差，但是矿工们还是发现在蒙大拿的Butte开采铜矿还是值得的。