View single post by Keith Pashina
 Posted: Mon Mar 20th, 2017 07:45 am
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Keith Pashina


Joined: Sun Nov 4th, 2012
Location: Minneapolis, Minnesota USA
Posts: 753

The inside of the Iron City (Frontenac Mill), showing Deister tables - a piece of equipment similar to, but differing from the more-commonly used Gilpin County bumping tables and Wilfley tables

More Ore Concentrating Equipment

Now, we’ll take a short look at what happened in the mills to further concentrate the ores after they passed through the stamps, crossed the amalgamation tables, and ran through the bumping tables and Wilfley tables. To make some generalizations, ore concentrates were handled by a variety of secondary concentrating processes, and the equipment used would make some very interesting models.
In my previous post on March 14, 2017, I listed the mills operating in 1917 – most used a simple combination of stamps, amalgamation plates and tables, and either Gilpin County Bumping Tables or Wilfiey tables, Only two mills at that time did anything different. However, the 1917 report is merely a “snapshot in time.”  Many of the mills evolved in their processing over time – we have already seen that in the Hidden Treasure Mill. This seemed to happen in many of the other mills also. So, when modeling an ore mill, I will need to select a particular year if I really want to be that accurate.
When the ores were crushed, there was a fine line between crushing the ore not enough or too much. If not crushed enough, the particles were too large to adhere to the mercury on amalagamation plates or separate easily on bumping tables. If the ore was crushed too fine, the slimes (fine particles suspended in water), would pass over the amalgamation equipment and bumping tables. It was inevitable that some particles would be very fine, and this one reason why secondary concentrating processes were also used at many mills.

The secondary concentrating equipment generally seemed to include three types of machinery:
1.     Concentrating tables or jigs
2.     Gravity separation in tanks or buddles
3.     Additional grinding equipment to rework the ores

The Card concentrating table for slimes - used in the Iron City/Frontenac Mill and others
More on Concentrating Tables 
To further concentrate the finely crushed ore particles, there were many different options available. Sometimes, a second group of Gilpin County bumping tables would be used. Wilfley tables were sometimes used, as well as Frue vanneers, Card tables, and Deister tables. All of these tables operated in a similar fashion – a bed with small ridges was bumped, shaken, or vibrated when the ore slurry passed over it. Often, the speed, ridge size, slope, etc. were customized for a certain size ore particle and specific sources of ores. This doesn’t really matter to me much – I care more about what the machinery looked like and its general location within the mill.
To me, all of these equipment looks similar, varying in size and general layout of operating drive wheels, gears, and movement arms. WIlfley tables are the only concentrating equipment I have seen offered as kits in my scale, HO, but I think they have been offered in O and maybe S, too.
I probably need to create a master for Gilpin County bumping tables, and either cast a few in resin, or print in 3D.

The Deister table was another type of concentrator used in some Black Hawk mills. This company is still in business manufacturing equipment for the mining industry

Example of a jig - this type may or may not have been used in Gilpin County mills. This type had a metal ore working box

I haven’t mentioned the other concentrating equipment group yet – jigs. These machines took the ore slurry, and agitated it in water with added chemicals. The chemicals were oils or oil-like compounds, and the agitation produced an oily froth to which gold particles adhered. The froth was skimmed from the top by the jig to collect the gold. Think of a washing machine type apparatus and you have the general idea.

What is interesting from a modeling point of view is that the jigs look like large square tubs with wheels and gearing on top. I have never seen these offered in kit form, but these would be relatively easy to model. Again, probably a candidate to cast in resin or print in 3D.

Another type of jig - this type has a lower wooden box. From remnants of jigs I have seen in Gilpin County, I think this type was more commonly used than the metal box type shown in the preceding photo. This wooden box type could be scratch built with some effort - I don't know how common the elaborate cast iron bracing shown was - the examples I have seen, although more modern, were much simpler
The next group of concentrator equipment were those that used gravity to separate out the heavier gold and other metals from the lighter crushed minerals. This will be my next post.


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