View single post by Keith Pashina
 Posted: Mon Feb 13th, 2017 09:00 am
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Keith Pashina

 

Joined: Sun Nov 4th, 2012
Location: Minneapolis, Minnesota USA
Posts: 750
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ORE PROCESSING IN THE HIDDEN TREASURE MILL - AN EXAMPLE

This image shows a very simplified flow chart of how ore moved through the Hidden Treasure Mill. This could be considered a snapshot in time, because the process evolved over time, as ores changes and the equipment or flow of ores needed to change. This flow chart represents the mill when it was at its peak production, and about the time most photos were taken of this mill
The first step was to unload the ore, and get it ready to feed into the stamp mill. In most cases, this consisted of dumping Gilpin ore carloads directly into ore bins, or sometimes into piles on the mill floor.  The ore had already been sorted out at the mine, and only ore with good values would have been shipped by rail. Some pieces were too large for the stamp mortar opening, so these were broken into smaller pieces using mauls and sledge hammers. From what I have read, no mechanized crushing was used here, such as jaw crushers, as used in other mining districts.  
The basic idea of a ore-processing mill is to break down the raw ore into smaller pieces, to liberate the gold (and other metals) and somehow concentrate it so it can be sent to a smelter for final processing. As we mentioned before, conventional stamp mills did not work well on the ore with higher amounts of sulphides. The technological breakthrough was the “Gilpin county stamp mill”. At first glance, it looks like a conventional stamp mill: 5 stamp heads lifted by tappets and grabbers, a mortar box the ore is crushed in, and a big wheel for the belt drive. But, the big differences are: 1) the stamps were lighter and dropped much slower and 2) the mortar box deeper and larger.


One piece of equipment you rarely saw in a Black Hawk mill was a jaw crusher, such as shown above. Although common in mills in many other districts in Colorado, these crushers were generally not needed at the Black Hawk mills. Each mill seems to have a customized set of equipment and ore handling methods, and no two seem to be alike. But, there seems to be an exception to every generalization that I make, so a few of the mills did have jaw crushers!  That said, labor was cheap, and hand breaking-up of ores and shoveling of ores was the preferred practice


Just for fun, I included this photo of a modern-era jaw crusher, from above. Note the electric motor at right - not common at the era I model, the early 1900s. The ore feed was from left to right, and ore slid down the chute at left into the top of the jaw crusher at center


Here is the "guts" of the Hidden Treasure Mill - the large bank of stamp mills - at least 50 stamp heads are visible here, and there were 25 more not shown in the mill not shown in this photo!  One thing that strikes me in these and other photos are the crowded nature of the mill - there is a lot of machinery, walkways, launders, belt drives and structural members all over the place. This would be a challenge to model, but very rewarding if pulled off correctly!










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