Description

An arrastra operated by a water wheel at the Providence Mine in the Big Bug District, Yavapai County, Arizona between Poland Junction and the mouth of the Poland Tunnel.

An arrastra was a primitive technology used to crush ore into a fine enough powder so that precious ores could be separated from host rock. Arrastras (also “rastra” or “arastra”) had their origins in Mexico. They were first used during the California Gold Rush of the 1850s. These devices consisted of a flat track of stone inside a low wall of rock or wood, a retaining basin to capture and hold the ore, and a center post and horizontal shaft made of wood or from small tree trunks. The ease by which they were built and operated made them ideally suited to small mining operations. Powered by horse or mule, the shaft would drag one or more large stones in a circular path on top of the flat stone base, crushing the ore that has been placed in the basin. Mercury was added to the resulting mix to help capture the gold as it was separated from the pulverized rock. When water was plentiful, as in this photograph, flumes and water wheels were used instead of animal-power. More elaborate arrastra mills were often housed in a building and powered by steam-driven machinery. Eventually, arrastras were replaced by much larger and more complex milling methods and stamp mills replaced arrastras at most mines when adequate capital was available.