Stamp; stamp; stamp! Boom; boom; boom! Imagine living close to a mine and it is in the 1890’s. Imagine how do they crush the quartz to derive the gold? Imagine feeling that stamping process in your bones, and hearing it from miles away! Stamp mills were close to the mines here in the Mother Lode, so let us take a tour of our experience at the Stamp Mill at Gold Bug Park.
The Stamp Mill is located a hop, skip and a jump from the Gold Bug Mine. This was the place where the mines in the area of Poverty Hill Mining District could crush the rock brought in to extract the gold that was hidden within! Hundreds of tons of ore were processed at this mill!
What is a stamp mill, you ask? It is where a giant mortar and pestle crunch ore into a powder.
A diagram of the stamp mill
The Stamp Mill at Gold Bug Park was established by the Joshua Hendy Iron Works of San Francisco. There is a frame that holds 8 iron stamps that has an ore loader at the top and at the bottom is a catch basin.
The drop bin where the ore entered the system for stamping
In the early days, they ran water 8 miles from the American River, quite a distance without using electricity, to drive a large belt that turned a really huge wheel that controlled the stamps!
The Wheel that controls the stamp
Later on they used an 12 cylinder Cadillac Engine to run this huge mechanism. The easiest way to explain how this device works is to think of an engine in a car. It has pistons which are moved by a crankshaft. Each piston is moved by the crankshaft at different intervals so that all the pistons are not up at the same time or down either. The sound of a working engine in your would be tap-tap-tap-tap. Same with the works in the Stamp Mill. Each stamp drops sequentially to crush the rock taken out of the mine. Here is a photo of a 1/8 scale model of the Stamp.
A one-eighth scale model of the stamp at the Stamp Mill
Each stamp weighs 1,500 pounds raise up between 12 – 18 inches and then drop on the ore below it at a rate of 100 hits per minute. Can you imagine that? This action results in pulverizing the ore below until it becomes a powder. The powder then has water washed through it and it goes through a fine mesh onto a table called a amalgamation table.
What is interesting about the amalgamation table is that the surface is coated with copper. The copper is painted with mercury as this will stick to the copper, but mercury will also stick to gold! So as the water mixes with the powder, which is called slurry, and it would go running down the table, and any gold in the powder will stick to the table! When the table is full of gold, they would scoop up what was on the table, mercury and gold together, forming a ball.
A sketch of men working on the amalgamation table
They take the combination to what is called a retort facility. The gold and the mercury are heated in a vessel to extract the mercury off the gold. This process would cause the mercury to evaporate and then the vapor would go through a cooling chamber to be re-used again on the amalgamation table. What was left in the vessel was called sponge gold. The reason for this is where the mercury has evaporated out of the gold it leaves holes, and resembles a sponge.
Retort mechanism
From there the gold is heated to 2,500 degrees to remove any of the impurities. Any impurities would float to the top, where they would then be skimmed off. Then the gold would be poured into molds to form bars that weighed 80 pounds each. The gold was then transported by the Wells Fargo Express to the U.S. mint located in San Francisco.
What was really interesting was that the docent who gave us this tour indicated that he had just had folks there from Colorado, who had gone on a mine tour in their State. The gold process there created bars of gold weighing over 400 pounds per bar to prevent theft!
We next heard about that scoundrel known as “Black Bart” and how he stole gold from the Wells Fargo Express 27 times before he was caught. They discovered who Black Bart was from a stamp on a handkerchief that was dry cleaned in San Francisco. It was the 93rd laundry that they visited where they were able to discover the true identity: It was Charles Earl Bolles. While he only confessed to only one robbery of the Wells Fargo Express it was believed that he actually committed 27 robberies of these wagons!
Charles Bolles – from the Wells Fargo Archives
Black Bart served 4 years of a 5 year sentence. At the 4th year, Wells Fargo went to where Black Bart was jailed. That was the at “new” prison called San Quentin. And, Wells Fargo struck a deal with him. If he refrained from robbing another Express wagon, they would bail him out. He took the deal, was released that day, and the Wells Fargo Express was not robbed again!
Again, if you are in the area, please do stop by and visit Gold Bug Park, the Gold Bug Mine and the Stamp Mill. It is well worth the trip. Did I mention that there are hiking trails? There are, and there is even an area to have a picnic lunch near the dam on Big Canyon Creek. And, if you would like to do a bit of gold panning you can! They have an are set up for this at a cost of $2/hour. If you do stop by, be sure to tell them that I sent you!
Life in the Foothills 