The Kern River Valley Historical Society has been in operation for over 40 years. Our mission is to preserve and communicate the rich and colorful history of this region. To achieve these goals we have established the Kern Valley Museum in downtown Kernville next to the Post Office.
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Our Big Stamp Mill

That big stamp mill in our museum’s back yard has filled me with questions...

from the first time I saw it.

Questions like: What are the names of all its parts? How fast did it run? How heavy are its stamps? When did they start using these mills? How big of ore could they feed into these mills? And on and on it went.

I found a booklet in the gift shop at the Empire Mine in Grass Valley titled The Stamp Mill by Roger P. Lescohler that answered all my questions. A picture is worth a thousand words so a cross section of a stamp mill is included here, as well as a picture of the mill being set up and the completed mill. Early on, stamps (stem, tappet, boss, and shoe) were fairly light around 400 to 600 lbs.

As time went on, they got heavier around 1200 to 2000 lbs. The most common stamp was between 1000 and 1500 lbs. Too heavy, too much down time in repairs. Too light, too much time wasted in crushing ore. The best amount of lift turned out to be between 5 and 8 inches. Too much lift increased wear, too little increased crushing time.

They ran the stamp mills as fast as they could which was 90 to 100 drops per stamp per minute. A three stamp mill like ours would produce 270 to300 drops per minute. Each stamp pounded 3 times every 2 seconds. The shaft, with the cams attached to it, would also turn 3 times every 2 seconds or 90 to 100 rpm. They could not run the mills faster than that because at a faster speed the stamp would not have time to drop down completely before the cam came around again resulting in the bottom of the tappet hitting the top of the cam. This would damage both the tappet and the cam. Also the crushing of the ore would be greatly reduced because the stamp would not be allowed to drop all the way down.

It took about 20 horsepower to run a stamp mill. It could be a water wheel, steam engine, or electric motor. A lot of trees were cut down for steam power. All of the ore before going into the stamp mill had to be broken down to about the size of an egg. This was done with a machine called a jaw breaker. Then the ore got pounded to a pulp in the mortar box of the stamp mill and went through a screen to the amalgamating plates. The average amount of gold was less than an ounce per ton of sand going over the plates.

The little bit of gold, in all that sand, had to find the mercury. The clean gold would combine with the mercury but the dirty gold, gold that was connected to other minerals or contaminated with something like oil or grease, would not. This process of using mercury is called “amalgamation”. They got about 60% to 65% of the gold this way. That is why cyanide was used in shaker boxes below the plates, to get the dirty gold. As a result of both processes they got a total of about 85% of the gold.

The most skilled, most honest, probably highest paid workers were the men who worked the amalgamating plates. This was where the payoff was at. All the work that was needed to get the gold to this point would have been lost if the men who worked with the mercury did not know what they were doing. They had to know their job well but, as a result, they probably did not live long lives. And I always thought that they got the new guys who didn’t know better to do that job!

—Ron Anderson



49 Big Blue Road
PO Box 651
Kernville, CA 93238
(760) 376-6683
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Thursday - Sunday

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