What is "chilean mill"

The Chilean mill was a machine used on gold fields in an early period of gold mining. The machine was composed of two rotating wheels the would revolve over a pan filled with gold-bearing rocks. The idea was that the wheels would break open the rocks with gold, so they could harvest gold from multiple rocks at a time.

One of the earliest such machines was built in Ballarat in Victoria, Australia during the Victorian gold rush and was combined with a sluice for extracting the gold.