Spotlight on the Kern Valley Museum: The Stamp Mill

Stamp Mill | KRV Museum

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Stamp Mill | KRV Museum

At the Kern Valley Museum, in the backyard, stands a splendid example of a gold ore crushing machine called a stamp mill. After the exposed gold (placer gold) was all found, what was left was the gold that was in quartz rock. Various machines were used to separate the gold, but many mining companies eventually chose the stamp mill. All stamp mills acted as giant sledgehammers that pulverized the gold-laden quartz rock into a fine powder called pulp when mixed with water. They did this by lifting solid steel rods with weights on the ends called mallets. These rods weighed from 700 to 1,500 pounds.

Like giant sledgehammers, these rods would come crashing down on steel platforms (dies), smashing the rocks. The action occurred in a cast iron box called a mortar with a screen in front of it. After being hit over and over, the rock (fine sand now), gold and water, called pulp, would splash through the screen unto an inclined platform where it would flow down the platform. To separate the gold from the water and fine sand, they lined the platform with copper sheets and then applied mercury to the copper sheets. When gold washed over the copper sheets, it stuck to the mercury, forming an alloy called amalgam. The finely crushed rock and water flowed on by.

This process usually obtained around 75% to 85% of the gold. Often a concentration table was placed below the incline to obtain as much as 90% of the gold. At the end of a shift, the stamp mill would be stopped, and the copper sheets would be scraped clean of the gold and mercury. Now the gold had to be separated from the mercury. They put it in an enclosed cast iron container called a retort. The retort had a sealed lid with a pipe coming off it.

Because the mercury is already a liquid at room temperature, when heated, it turned into a vapor before the gold melted. The vaporized mercury went through a tube at the top of the vessel, where it cooled, then turned into a liquid and dripped into a jar to be used again on the copper sheets. This process left the gold by itself. Unfortunately, mercury is very poisonous. Those workers who worked at the stamp mills were probably the highest-paid workers but probably had the shortest lives. Our stamp mill is from the French Meadow Gold Mine in the Piute Mountains. It operated there from 1900 to 1907.

My description of how a stamp mill works is very brief. An excellent source of information is the Bob Powers book titled, "Kern River Country." It's on sale at the museum. Drop by the museum and see the many great displays. We are open from 10 a.m. to 4 p.m., Thursday through Sunday. We are located at 49 Big Blue in Kernville, right beside the post office. Remember – admission is free.

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