An Arrastre is a primitive mill for grinding and pulverizing ore. When viewing the Arrastre (also spelled Arrastra), you will see the mill comprising a circular, rock-lined pit in which broken ore is pulverized by stones, attached to horizontal pole fastened in a central pillar, which stones are dragged around the pit.
An arrastra, also known as a Mexican Rastra, was a primitive method used by early miners to process gold and silver ores. It was introduced to the new world by the Spanish in the 1500’s. They were used throughout the world, often at remote locations where other processing methods were not feasible. It’s simple yet effective design made it a valuable tool for the early prospectors to process ore on location, without having to transport tons of material to a stamp mill.
Arrastras were designed to extract the valuable gold or silver that was locked in host material. Unlike placer mining, gold that is mined from lode sources require crushing to extract the gold from rock. The basic design generally used large flat stones that were dragged around a circular pit made from flat stones. The drag stones were attached to a central pivot which allowed them to be dragged repeatedly over the ore that was placed in the arrastra.
They were typically powered by horses or mules, although some were powered by waterwheels and even steam engines in later years. The ore was placed in the arrastra, generally a few hundred pounds at a time.
Since each one was built on location, they were each somewhat unique in size and construction, although the basic designs were all more or less the same. The ore would be pulverized under the large stones until it was broken down to a coarse dust that could be further processed by the miners.
The simplest form of the Arrastra, which ours is, is two or more flat-bottomed drag stones placed in a circular pit paved with flat stones, and connected to a center post by a long arm. With a horse, mule or human providing power at the other end of the arm, the stones were dragged slowly around in a circle, crushing the ore. Ours is designed to be powered by a mule or willing human.
Our Arrastra at Superstition Mountain Museum was constructed by volunteers and is based on information gathered on original arrastras. The goal was to provide a mining example that is interactive and can be operated similar to an actual arrastra. The Arrastra stone was obtained by a volunteer and comes from the Wickenburg, AZ area.
Related: Arrastra (Wikipedia)