The workers crushed the rock to release the gold, concentrated the gold by gravity methods, and then exposed the concentrate to mercury that would amalgamate or mix with the gold. Miners call this kind of gold extraction free milling. Gold existed elsewhere in the Black Hills, but it was not in a state suitable for free-milling. In these conditions, gold was chemically bound to the rock, and very difficult to remove. It was called refractory gold ore. For many years, the Homestake operated as the only major gold mine in the Black Hills. Chlorization and smelting were seen as two methods that could remove gold from the refractory ore in the 1890s. More rock mining regions opened up around Lead and Deadwood because of this discovery.