A Word on paydirt classification….
by Mdv | Mar 5, 2018 .
Gold miners are a creative lot. We are constantly trying to improve our processes and methodologies. Too, we are always attempting to reduce the amount of time and effort it takes to recover the yellow metal.
However, in our rush to find the perfect way to recover gold with the least amount of effort, we at times have a tendency to want to ignore or discount the science that governs gravity gold recovery processes…i.e. classification.
Invariably it goes like this, “I’m looking for the right equipment that will enable me to stop classifying my material.”
It’s one thing to be creative, but it’s another thing to be ignorant.
When it comes to classification, it would not be necessary if it were not for the fact of "hydraulic equivalence" see (Doc's videos at Goldhog.com). Simply stated, if you take two pieces of material and subject them both to the same volume and velocity of water flow, the heavier one will stay in place longer than the lighter one. Therefore, if you want to separate gold (heavy) from everything else (lighter), they particles need to be approximately the same size (classification).
If you ignore this scientific principle and subject everything (all sizes of all material) to the same water flow, you are going to wash out some particles of gold because they are the hydraulically equivalent to a larger particle of lighter material. There is no way around this…it is a fact…accept it. The real question is: HOW do I include classification in my processes in a way that is the most cost efficient and least labor intensive?
To me, the answer is pretty simple…a trommel.
I have seen 4-inch diameter rocks fed into a Gold Cube system…with a trommel on top…no manual classification required…but we all know that a Gold Cube works best if the material is classified. The trommel on the Gold Cube usually has 3/16″ holes, and everything else is classified out…effortlessly.
If you watch the Gold Rush TV show and pay close attention, you will see all manner of classifying devices, from De-Rockers to shakers to trommels. But the goal is the same, to feed the sluice with material that is approximately the same size.
Now there is clearly a range of sizes going through most commercial plants that includes far larger material than what you or I would run through our operations, but the principle is the same…hydraulic equivalence is a fact…the material has to be classified…one way or another.
You won’t see anyone dumping huge rocks into their sluices, because, a big rock in a sluice creates unwanted turbulence and destroys the exchange/capture function of just about any sluice. This is not the hydraulic equivalence principle at work; nevertheless, it points out the necessity and practice of classification to successfully recover gold with a gravity recovery system.
Our next trommel will likely include three sluices and three sections of screens, from small to larger…each with a specially designed sluice to accommodate the size of the material being fed into it.
Don’t fight the facts, go with the flow, and find a way to design your gold recovery equipment that does the classification for you…like a trommel.
PS-do not rely 100% on visual inspection of the large material after classifying...pan it! Gold has a tendency to cling to larger pieces of material...you may be surprised at what you find.
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