Thursday, March 5, 2015

All About Shaker Tables (Part 1)

 (A gold shaker table from Tenta Trading.)

In this post I'll be discussing shaker tables, a topic you won't hear much about in most gold prospecting and mining books or websites. One reason for this is that most source material devoted to small-scale mining is primarily focused on getting the gold, not processing gold concentrates. However, if you're serious about your placer mining and approach it on a larger scale than most, then a shaker table is a must if you're determined to get every bit of gold out of your concentrates.

Ingenious Contraptions

Shaker tables (a.k.a "shaking" tables or wet tables) are pretty ingenious contraptions. No doubt you've seen them used on various gold mining TV reality shows so you already have at least a minimal idea of what they are and how they work. Essentially, shaker tables remove the gold from concentrates generated by various types of mining equipment. That gear could be as simple as a sluice box or suction dredge or as complex as a full-scale commercial mining wash plant with trommel. The generator of those gold concentrates really doesn't matter...a shaker table will efficiently separate the gold from those concentrates with minimal effort on your part.

The majority of shaker table designs incorporate the following elements or features:

A riffled deck atop some sort of support structure (usually braced posts or "legs"). Deck sizes usually run anywhere from 18 to 50 inches for test type shakers all the way up to big boys that measure seven by 15 feet. These latter are used in larger commercial mining operations of course.

At least half of the shaker's deck is covered with small riffles that are usually no higher than an inch or so. There is some slight variation in riffle design from model to model and these variations are meant to handle specific concentrate processing needs. However, I wouldn't get too hung up on the riffle design issue if I were you. They all work pretty damn well.
Deck configurations that are either rectangular (roughly so, anyway) or diagonal. In rectangular deck configurations, the riffles usually parallel the length of the rectangle itself. Diagonal deck models can handle larger amounts of concentrates and many miners swear they do a better job with very fine gold particles and provide an overall cleaner end product. Although this is probably true, you know how miners are...we tend to get stuck on our favorite devices or designs and then swear by them, no matter what!

Decks are most often constructed of wood and then lined with linoleum, rubber, or some sort of resistant plastic because these materials all have a high friction coefficient which helps in gold recovery. The most expensive (and probably the best) shaker tables are made completely from molded fiberglass, including the riffles which are part of the mold.

(Example of an out-of-use diagonal shaker table.)

A motor (typically electric) that powers the unit and connects to a vibration or shaking arm that "shakes" the deck. No rocket science explanation needed here methinks. One thing to note here though is that regardless of the shaker table deck configuration, the shaking motion is always parallel to the pattern and layout of the riffles.

A feed box hopper. This is where concentrates are loaded for table processing. Feed boxes are usually located to one side of the shaker and depending on the table size and design can be "fed" using a spoon, a hand trowel, or even a regular miner's shovel.

(Gold moving across a shaker table. Courtesy MSI Mining.)

Wash water feed line(s), pump, and/or sprayer. As you well know, gravity concentration methods using water are the most common and most efficient means of concentrating gold. In fact, this is the premise that's sustained small-scale gold miners throughout written history and probably well before that. Shaker tables aren't known as "wet" tables for no reason. Wash water can be fed by line or hose, or pumped or sprayed lightly onto the deck (thus the "wet deck" moniker) of the shaker to assist in concentration. In certain models water feed lines (hoses), or pumps and fine water sprayers are used in combination. Whatever the case, the water is usually fed onto the table at right angles to the shaking motion.

Here's the poor man's version of how the entire kit and kaboodle works:

A slurry (most often a mixture containing about 25% solid concentrates) is fed with wash water along the top of the shaker table. The motor shakes the table along its length using a slow forward "crawl" motion and then a fairly rapid return "strike" or jolt. This causes the gold, including coarser pieces and flakes, to move diagonally across the deck from the feed source and then separate on the table deck according to size and weight. Gold particles tend to layer or "stratify" in the pockets behind the riffles (no surprise here, right?). Interestingly enough, the shaker table's motion causes both the finest and the heaviest gold particles to the bottom of the deck behind the riffles while the coarsest (yep, you heard right) and the lightest particles remain near the top. These particle layers are then transported by a thin film of water across the riffles every time more feed is added to the unit. Since the riffles are invariably tapered and shorter on one end (the concentrate end) finer and denser gold particles are eventually shaken out in that direction where the water film flowing across their tips washes the lighter material away. The final concentration of black-sandless gold occurs in a trap depression at the end of the table.

There's more to come, so stay tuned.

(c) Jim Rocha (J.R.) 2015

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