Crushing Gold Ore

An arrastra was a primitive mill used to crush ore and extract gold and silver. Water diverted from Willow Creek turned a large water wheel for power, and a drive shaft connected to the wheel rotated cogwheels that dragged stones around a basin to crush the ore. Miners hauled ore to this arrastra and placed it into the basin to be crushed. Once the ore was broken into smaller pieces, the operator poured mercury into the basin, continued grinding, rinsed out the rock fines, added more ore, and repeated the process. After the ore had been pulverized, the amalgam-gold captured within the mercury was carefully recovered from low places and crevices on the arrastra floor. The amalgam was then heated and distilled to recover the gold, and the mercury was saved for reuse. Arrastras had been widely used throughout the Mediterranean region since Phoenician times, and the Spanish introduced the technique to the New World in the fifteen hundreds. Because they could be built from local materials and required little investment capital, they were well suited to remote areas such as South Pass City.

Wyoming · United States