Stamp mills are for crushing rocks by dropping a battering ram repeatedly.  The idea is to “liberate” the minerals by crushing the rock so that the particles were the same size as the mineral grains (in this case the copper). Then the heavier copper could be separated by gravity in the mill. The stamps were mounted on high platforms so the crushed rock could be easily removed as they crushed. Here the crushed rock fell into railroad cars which filled up and then rolled over to the next mill for separation and smelting. Continous operation of the stamp mill was noisy!

Here the stamp mills have mostly (all but one) been removed and the metal used has been recycled.