A Placer Mine is a unique creation by Mother Nature. Placer is pronounced so as to rhyme with glass-er.

As the earth was formed many minerals filled cracks created as the earth cooled and reshaped itself. These are the mineralized veins that create what are referred to as "Lode" mines. Lode mines are generally mined underground.

In creating a placer mine the forces of nature -- the wind, the rain, the snow and freezing temperatures -- have broken apart the rocks that contain the veins structure and freed the gold and other minerals from the rock. This "Free Gold" is now carried away with the wind and water.

Since gold, and many of the other minerals, is much heavier than the host rock the gold get trapped in crevices and little pockets. In fact, any time the water, or the wind, that is carrying the gold slows down the gold will settle out.

If the gold is bring carried by water in a stream or river then the gold will settle whenever the water slows down. The water will slow if the river levels out and it will also slow on the inside of any bend in the river. This is why the miners and prospectors always search sandbars for gold. Since gold is heavier than the surrounding materials it has a tendancy to work its way deeper and deeper into the material it has collected with. It will continue to work its way down until it reaches "bedrock."

This is why the richest parts of a placer mine are deeper down toward bedrock. Many times the material on top has no value at all and is referred to as "overburden" because it is just that -- a burden that is over the top of what we want to get out.

A placer mine is much cheaper and easier to set up. The amount of gold is way, way less than in most lode mines, but the placer gold is much, much easier to collect. With a placer mine you are working on top of the ground, not underground. You don't need all the lights, bracing, and explosives for a placer mine.

We will use a Trommel, which is nothing more than a revolving screen for sorting the large rocks out of the material that we want to put through our sluice box. The dirt, sand, and gravel that we want to put through the sluice box is fed into the trommel hopper. From there it passes through the trommel where it is sorted. The large rocks fall out of the lower end of the trommel and are taken out of the way by a conveyor belt. The "undersize," which is what falls through the holes in the trommel, go into the sluice box. It is in the sluice box that the gold is collected and oncentrated.

End View of a Trommel The small circle represents the water spray bar. Water is pumped into the spray bar under pressure and comes out a of a series of spray nozzles. This will wash the dirt off the large rocks so we don't throw any gold away. The spray bar is stationary while the barrel of the trommel revolves around it. A small drill will put holes in the pipe to act as the nozzles. The number of nozzles and size of the nozzles sets the water pressure. By holding the pressure at 100 psi the spray bar can be made from a piece of Schedule 40 PVC pipe. The four bars, sometimes there are five or six, are to make sure the material in the trommel is thoroughly tumbled and washed.

The end view of a sluice box, which is shown to the left, shows the simplicity behind the box. The drawing is an exploded view so each part may be clearly seen. National Gold uses a sluice box that is 24 inches inside width and just under 12 inches in height. This way we take a 4 foot by 8 foot sheet of aluminum and have it bent for us. Because we insist on a full 24 inches inside, and because we have about 1/4 of an inch rolled on the top edge so we don't cut ourselves, the sides are just under 12 inches high.

The small box represents the "matting" that is always placed in the bottom of a sluice box. The purpose for the matting is to trap the fine gold and keep it from going out the end of the box into the tailings pile.

We have seen many different types of matting used. Virtually anything that has pockets, or is fibrous will work. Some things just work better than others. We have seen indoor/outdoor carpet, regular carpet, burlap sacks, and even old clothes.

National Gold prefers to use conveyor belt lagging. It is a piece of solid rubber than can be cut 2 feet wide so as to fit the box exactly. You do not want pieces any longer than 4 feet because of the weight involved in handling it when it has all of the dirt and concentrates setting on it. At the end of the day you are already tired and you don't need to have to fight the matting in order to clean out the sluice box.

With the conveyor belt lagging we simply stand it on its side and wash it with a garden hose. Do not spray, just let the hose run normally. This will wash all of the gold out of the myriad of little pockets in the lagging. We simply do this in the sluice box, starting at the lower end, and catch the gold and concentrates in a wash tub at the end of the sluice box.

If you are interested in setting up your own operation go to the local conveyor belt company and ask to see their belt lagging. It has little pockets all over it. The sides of the pockets are lower than the ends so washing the material out of the pockets over the sides becomes much easier.

If you use the burlap or carpet you will have to rinse it out in the wash tub and this can be a real chore. Not only that it is almost impossible to get all of the gold out of the burlap and carpet so eventually you will have to burn the matting and pan the ashes to get the rest of your gold.

The larger box, in the drawing, represents the riffles.

Here again, anything that will break up the smooth flow of the water and let the gold settle to the bottom will work for a riffle.

We have seen riffles made out of almost everything imaginable. We have seen the riffles laid crosswise in the box, which we prefer, and we have seen them laid lengthwise in the box. We have seen wire mesh screens, sticks, and metal used for riffles.

Whatever is used, must be pressed down into the matting so that a tight seal is made so water will not come under the riffle and wash out the concentrates that are trying to collect.

The cut-away drawing shows the relationship between the sluice box, the matting, the riffles, and the direction of water flow. National Gold uses steel riffles that are 2 inches high with the cross bars being made from steel bar that is 2 1/2 inches high. By the time the 2 1/2 inch bar is tilted so that the top and bottom are flush with the 2 inch side pieces the slope of the cross bars is right where it needs to be for the optimum collection of fine gold.

Even though the sluice box has no moving parts and basically just sits there, it is the key to the entire placer operation. If it is not level from side to side then the water will slow at the low point and cause the riffles to clog and not function properly. It it is not uniform in its slope from start to finish then the water will slow where the box flattens out and cause the riffle to clog and not function properly. The speed at which the water flows through the sluice box is critical. The water speed is controled by the slope of the sluice box. If it is too steep then the fine gold will be washed out. If it is not steep enough then the washing action will not work properly and everything will be collected -- which clogs the riffles and causes them to not work.

When the sluice box is operating properly the riffles will cause an eddy effect on the downstream side. This eddy disrupts the smooth flow of the water and causes the heavy minerals to be deposited. As the day wears on, the heavier minerals work their way deeper and deeper into the material collected so that by the end of a days run, the heaviest concentration of gold will be found at the start of the sluice box. The gold will have forced the lighter minerals out so they will be recaptured further down the sluice box.

In order to establish the proper water speed you need to understand that the faster the water moves the heavier the material it will take with it. For instance, when we were mining with the 14 inch suction dredge on the Klamath River I was standing near the end of the sluice box and reached down and picked a softball sized rock off the surface of the water. Needless to say we shut down immediately and revamped the sluice system to slow down the water. All we were doing was moving the gold from one place to another without collecting any along the way.

It is very simple to set the slope of the sluice box. Initially, the slope should be set to 1 inch of fall for each foot of length. That means that a 40 foot sluice box will have a total drop of 40 inches. In order to set this without expensive surveying equipment you need a ball of twine and a "line level." A line level is a device that has a leveling bubble and will hook to your twine.

Fasten one end of the twine to the spot where the top of your sluice box will be. Go to the bottom end of where your sluice box will end and have someone hold a 2 x 4 upright. Stretch the string down to the 2 x 4 and make sure it is level by checking with the line level.

Mark the spot on the 2 x 4 and measure down the distance you need. Mark this spot also. This is where the top of the sluice box will be at its lower end. Now, put a stake in the ground and tie the twine off on the stake at the lower mark on the 2 x 4. Now you are ready to put the sluice box in place. As you install the sluice box you can bring the top of it up to the twine and level across with a common carpenter's level.

If you plan ahead you can make the sluice box adjustable by building the box with trailer hitch cranks for legs. This will give enough flexibility to raise and lower the end several inches. You must still keep the slope uniform the full length of the box. To do this simply run your twine back down the top of the box and then move the end the distance and direction you need in order to adjust the box. Then, you can adjust each of the cranks to move the box to the new slope.

There are not many things more beautiful than after a long day to turn off the water and see the front 8 to 10 feet of the sluice box an almost solid yellow color. And, of course, since the nuggets are heavier than anything else, this is where you will find the nuggets, if there are any. It needs to be carefully pointed out that if all you have is nuggets you probably will not be able to make money on your mining operation. Typically over 80% of the gold in a placer mine is fine gold -- sometimes referred to as flour gold. If you do not collect this you are wasting your time and throwing good money away.

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When it all gets put together this is what it looks like:

National Gold's French Corral Placer Mine -- In Operation