There are various ways to recover fine gold from black sand concentrates. The four primary methods or devices used are panning, Gold Wheels, Blue Bowls, and Miller Tables. They’re all effective to varying degrees but only one stands out on top. Here is a description of each method and its effectiveness.
You can take an entire pan of black sand concentrates, pan it all the way down, and get the majority of the gold but, you won’t get it all unless you have professional panning skills.There are two variables that must be considered when choosing to pan out your concentrates.
The first is the amount of cons that you’re panning out at any given time. I pan out no more than 2 tablespoons of concentrates at a time to minimize gold loss. The more cons your dealing with in the pan the greater the risk of having gold slip out under the radar.
The second variable is classifying before panning . It is more efficient and effective to pan out concentrates that are the same size. This means classifying your cons with a screen into separate mesh sizes. The majority of the time I use a gold cube and trommel. This classifies material to 3/16” (slightly larger than 8 mesh) so when panning out my cons I use a 12 and 20 mesh screen. This separates my concentrates into +12, -12 +20, and -20. It is a good idea to classify your material into at least 3 different sizes before panning. These sizes will vary depending on what mesh size your material is to begin with.
Overall, Panning your concentrates is inexpensive and effective but is very time consuming and requires a lot of patience. This method has been used for centuries but lucky for us, technology and innovative miners have developed much more effective alternatives.
The next device is a Gold Wheel or Spiral Wheel. These devices require a lot of adjustments and can take a lot of time to get functioning just right. This is the main reason it would be my last choice in fine gold recovery devices. It seldom works the way it’s supposed to in my experience. It could be operator error but most people seem to have issues with it.
A gold wheel is a wheel-like disc that has spiral riffles leading to a hole in the middle. When properly adjusted, running water cups and spills out at the bottom of the wheel. Material is fed at the bottom while the spiral riffles slowly carry the heavies up and in to a hole in the middle. When working properly, the spiral riffles will carry somewhat clean gold into the hole and into a small container. This device will recover fine gold and minimize black sand but can become quite frustrating to deal with.
The next device is the Blue Bowl. This device has become quite popular recently. A blue bowl is a cake pan-like device that uses water current and centrifugal force to separate gold from black sand. It can be very effective but also requires a lot of set up and adjusting. It requires you to classify your material to a minimum of 20 mesh but works best if classified into 20,50, and 100 mesh then ran individually.
In my experience, it takes way too much time and effort to get everything working just right on a blue bowl and material usually has to be ran more than once to get all the gold. One positive thing about blue bowls is a full set up is pretty inexpensive.
Last but certainly not least is the Miller Table. This device stands out on top due to its simplistic yet highly effective design. Miller tables are like sluices but with out any Hungarian riffles, matting, or carpet inside. The floor of the table sometimes has a rough surface that if looked at closer, has small microscopic indentations that cause low pressure zones to catch extremely fine gold. A small pump (usually around 500 gph) recirculates water through the miller table. Miller tables have simple valves to control water speed.
The miller table works by allowing water to wash away all the light material and eventually black sand from the gold. The water pushes down on the fine gold (usually flat) causing the gold to stay put while all the black sand is washed away. A fine haired paint brush is used to brush up the material and eventually brush the gold into a pile or into a hole that collects the gold. Most Miller tables require material to be 20 mesh or smaller but there is no need to classify into separate/smaller sizes.
The Miller table is a tried and true method for recovering fine gold. It is very simple and requires very little assembly or preparation. You usually only need to run your concentrates once and there is no need to run different mesh sizes separately. Fine gold concentrates can be ran on a miller table in half the time it takes to pan your concentrates. Next time your about to start panning out your fine gold think about how fast and easy it would be to use a Miller table.
Here are my top Pics on Miller Tables. Click on the images below to view specifics.