View single post by Keith Pashina
 Posted: Mon Feb 13th, 2017 08:11 am
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Keith Pashina


Joined: Sun Nov 4th, 2012
Location: Minneapolis, Minnesota USA
Posts: 781
These stamp mills were fed by hand-shoveling the ore in the rear (ore bin side) of the stamp mill. From what I have been read (and told by those individuals who would know this stuff), no mechanized ore feeders were used in the Black Hawk mills.
 This is a flow chart I used in a presentation the 2014 Narrow Gauge Convention, and shows part of the ore handling methods. The stamp battery (the stamp mill machine in side the stamp mill building - whew! confusing, isn't it?) was probably the most important part of the mill. This machine did two critical steps, and until alternative crushing methods became more popular, this was the "Gold Standard" process (sorry, I couldn't resist the pun)

This is what a Gilpin County stamp battery looked like. This restored example sits in front of the Gilpin County Historical Society Museum in Central City. Note the gear drive on this mill (some had wooden bull wheels)

This image is representative of a stamp mortar battery - a cast iron box where amalgamation and crushing took place. These objects were heavily built to withstand the crushing forces and vibrations

Each stamp mill had 5 stamps each, and stamp mills were ganged up to attain whatever capacity the mill needed to handle. So, the Wheeler Mill had 40 stamps, meaning they would have had 8 stamp mills inside, and the Hidden Treasure Mill had 75 stamps – 15 stamp mills, at its peak production.
The stamp mills did vary, depending on each mill’s preferences. Some representative sizes were:
·       550# - the weight of each stamp head
·       18” – the drop height of each individual stamp head
·       30 – number of drops per minute
·       18” – depth of the mortar box
By enlarging the mortar box and slowing down the stamping, the ore was crushed to a smaller size, and stayed longer inside the mortar box, Unlike other stamp mills, that just crushed the ore, the Gilpin county stamp mill also used amalgamation inside the mortar box. The ore was gradually crushed and churned around in the mortar box by the stamps, along with the mercury. Some of the gold consequently adhered to the mercury that was on the amalgamation plates, and was cleaned off later. The remaining ore, after some time, eventually was small enough to pass out through the exit screen, and on to the third step of the process – more amalgamation tables.

The rear of a stamp battery - the narrow slot is where the ore was shoveled in, by hand, of course

The "front" of the stamp  battery - although slightly ajar, you can see the screen at the front of the stamp battery - the ore had to be crushed very fine to pass through the small sieve openings

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