How Stamp Mills Work:
A stamp mill is a large mechanical device used to crush ore and extract the desired metals from rock – the host material. It uses heavy steel stamps to pound and break apart rock, releasing the valuable metals from worthless rock, allowing for the extraction of gold and silver for further refining.
The basic design of a stamp mill has been used for thousands of years for a variety of crushing applications. Its traditional use has been for the processing of mineral extraction, whether it is copper, silver, gold, or any other metal contained within host rock. The first stamp mill in the United States was built in 1829 near Charlotte, North Carolina.
Stamp mills during the early gold rush days were generally powered by water, although sometimes steam engines were used as a power source. Their construction typically involves a series of heavy metal stamps arranged in a wooden frame called a stamp battery. A system of rotating shaft and cam is used to raise and lower the stamps on top of the ore. Stamps were usually built in banks of five and the number of banks built and used varied with the amount of ore needing to be processed. Smaller mills were often composed of only one bank of five, some were composed of two banks of five and this one on the museum property was one of the largest – a 20-stamp mill, four banks of five. The stamps themselves are extremely big and heavy, made from steel or cast iron heavy enough to pulverize the ore beneath. The stamps are repeatedly raised and dropped onto ore that is fed into the mill, until the coarse chunks of ore are reduced to finer material capable of further processing.
The stamp mill provided an invaluable need for the early gold miners. Unlike placer deposits that produced gold nuggets already separated from rock, lode gold deposits were of little value if the gold could not be efficiently removed from the host rock. With the ore crushed into fine powder and the gold released from its host, the amalgamation process with mercury or cyanide could be done, allowing for the final extraction of the gold.
- Superstition Mountain Museum's 20-Stamp Ore Mill - Tri-fold Flyer (.pdf, 301kb)
- Wikipedia: Stamp Mill