View single post by Keith Pashina
 Posted: Sun Feb 19th, 2017 09:02 am
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Keith Pashina

 

Joined: Sun Nov 4th, 2012
Location: Minneapolis, Minnesota USA
Posts: 733
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The inside of the Hidden Treasure Mill, showing the stamps and amalgamation tables at the rear, with a line of Gilpin County Bumping Tables in front, used to concentrate the ore's metal content further
CONCENTRATING TABLES
 
After moving through the stamp mills, amalgamation tables and mortar boxes, and blankets, the ore slurry moved to concentration equipment.
 
For the time period I am interested in modeling, a limited amount of processes were used to concentrate the ore.  In later years, that is, after about 1900 or so, other processes were introduced into the area mills.
 
The Black Hawk mills favored a concentrator called, naturally enough, the Gilpin County Bumping Table.  If you’re familiar with gold panning, you basically separate the gold particles from the sands and gravel by agitating a mixture of rocks and water. The lighter density quartz and other minerals wash away first, leaving the heavier gold behind. The bumping table used a similar concept, although mechanized.

Generally, a Gilpin County Bumping Table was like a gently sloping metal sluice flat on the bottom. Ore slurry was introduced at one end of the table, and it was bumped back and forth (front to back), about 1 ½ to 3 inches 2 to 3 times per second. The bumping action moved the heavier gold particles up the slope to the front of the table, and the water would wash the lighter particles down to the bottom of the table. This table was developed and manufactured locally, and doesn’t seem to have very popular outside of the county.
 
Photos of mills show that 2 or more tables were paired with each stamp battery. The Hidde Treasure Mill, for example, had 20 tables, in 10 groups of 2. Modeling these tables would be a challenge, as to my knowledge no commercially made kits have ever been offered by anybody. However, these tables are also a key, distinctive feature in almost any of the mills, and worthy of being modeled.

Another concentrator used alongside the Gilpin County Bumping Tables was the Frue Vanner. This machine was first manufactured in the 1860s, and introduced in the Black Hawk mills in the late 1800s.  The term “vanner” comes from the word van, which means to wash ore on a flat shovel. The Frue Vanner differed from a bumping table, in that there was a gently sloped continuous belt shaken from side to side (whereas a bumping table was bumped back and forth).  Some sources say a large vanner was about 14’ long by 9’ wide and sat about 5’ tall, and the belt itself about 4’ wide by 12’ long. A smaller vanner had 4’ wide belt. The table was shaken side to side about 1”, and the belt rotated and moved about 3’ per minute. The lighter, non-metal waste separated to the top and was gradually washed away, and ore concentrate stayed on the table, moved to the end of the table, and was collected.


 Above, a Frue Vanner


Another popular concentrator was the Wilfley table, invented in western Colorado in the late 1890s. The table shook back and forth, and a series of riffles on the surface aided in separating light waste rock from heavier mineral concentrates. Probably more common in other mining districts, some Black Hawk mills did use them. This is good news for modelers, because kits have been offered in O and HO scales, and maybe others, too.




 
Yet one other concentrator used was Deister table. This was used in some mills, and looks similar to Wilfley or other tables. There is a side mechanism that actuates the shaking action, where Wilfley tables seem to have this mechanism on the narrow end. To model one, perhaps a Wilfley table kit could be used.
 




`Remember, I am greatly simplifying the explanation of how the mills worked, but for my purposes, I really don’t need to know all that much, just enough to make a plausible model. Although there are many very technical methods and adjustments going on in a mill, miniature models, at least in the smaller scales, don’t need to show all the nuances.

There is a lot more going on in the mills, and we’ll look at some of the other machinery next.


Keith

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