A stamp mill is a large mechanical device used to crush ore and extract the desired metals from the host material. It uses heavy steel stamps to crush and break apart material, releasing the valuable gold from worthless rock, allowing for the extraction of gold 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.
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 are built 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 ore is 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 gold released from its host, the amalgamation process with mercury could be done, allowing for the final extraction of the gold.
It is worth noting that today, some gold in quartz specimens hold additional value that is much higher than the price of the gold contained within them. With this in mind, the vast majority of gold ore does not have special value to collectors, and still need to be crushed in order to extract the precious metals from the rock.
Building a stamp mill was a sizable undertaking, and most were operated by large mining companies rather than individual gold prospectors. Smaller operations often used an arrastra for grinding up metal ores.