To separate minerals from a rock, the rock is usually crushed. One way to crush is to break the rock by stamping it with force.  The idea is to “liberate” the minerals by reducing the grain size of the rock to the size of the minerals. This typically requires a lot of energy and equipment at a stamp mill.  So at the mine, the rock is broken only enough to get it into an ore car. At the mine site, poor rock is separated from ore.  The ore is then transported to the stamp mill, often miles away (Gay is about 11 miles from Mohawk).  At the mill the rock is crushed to a fine size, in order to separate the minerals.  Copper is much heavier than other minerals so it can be separated by gravity.  Stamp mills are often near the shore because they can get fuel to run the mill by boat, and they can ship the ore by boat. After the stamp mill mineral separation there is a lot of waste rock which is sand and silt size---this is the stamp sand.