BY DON PADGETT
During my fourteen years of mining throughout the United States, with a variety of gold mining equipment, I’ve seen and processed a lot of black sand. And since the mining equipment I’ve used has ranged in size from gold pans and suction dredges to Caterpillars and heavy equipment, its been possible to approach “fine placer gold recovery” and its liberation from black and blonde sands from virtually every level.
Learning in any form takes time and usually a lot of practice, which all too often includes making a few mistakes. So I might as well begin this article by admitting that I’ve certainly left my share of gold on the ground, even after all the hard work of getting it out of some of nature’s most elusive hiding places.
Liberating gold from black sand can be a very difficult process, especially when the gold is extremely fine. The finer the gold, the more difficult the recovery seems to be. And whether you’re an experienced miner or a novice, it is certainly a waste to walk away from your fine gold, leaving it half processed in a pile of black and blonde’ sands at your clean-up site along the river bank or in your campground. For example, let me relate a true story of one of my own recent experiences:
During a recent winter, after a fairly good dredging season, the cold water and my own curiosity caused me to wander around and check out some of the black sand piles (left behind by other miners) I had noticed earlier in the season. Knowing from my own experiences how miners tend to lose gold during clean-up, I took along my gold pan to test with; and sure enough, in the first pile of sand I found two nuggets (about 1/4 and ½-pennyweight) along with plenty of color. I immediately went back to camp and returned shortly with my shovel and some buckets which I used to transport the heavy black sands back to my campsite where I do my own clean-ups. I use an industrial-type spiral-wheel which is larger and faster than the typical gold wheel sold in most mining supply stores. Gold wheels will do a great job of fine gold recovery providing they are set up and used properly. And since every wheel and concentrate deposit is unique, your ability to tune your wheel and work your sands will be the critical factors affecting your fine gold recovery, not a particular brand name.
During the past few months, I’ve also been running the final clean-ups from a number of mining operations along the Klamath River in northern California. In most cases what were only five gallon buckets of “previously processed” black sands magically changed within a few hours into literally pennyweights and ounces of liberated fine gold. You can just imagine the surprise and excitement experienced by these dredge operators when they saw that the black sand byproduct they had so very often considered “nearly worthless” or “unrecoverable” was in fact valuable and could even pay a substantial portion of their operating expenses.
Most of what I’ve learned was to a large extent the result of associating with some of the best clean-up men in the gold mining fields of Alaska. They had been liberating gold for more than fifty years when I first met them, and many are probably still at it today. If there is a single and most important key to unlocking the mysteries of fine gold recovery, it is “the basics always work.” So if you’re in fine gold, and you’re not able to recover it, remember to return to the basics.
What follows is a simple step-by-step process of the basics of fine gold recovery:
Without Classification, Liberation is not Possible
Virtually every piece of modern mining equipment currently available in local mining and equipment shops has its own inherent system of material classification. To classify, in mining terminology, simply means to separate the material (rocks, gold, and sand) by size and/or weight (usually by size). It only makes sense to take this process even further in handling the clean up of your concentrates.
Classification is often accomplished by using screens of various sizes or meshes, and while many gold miners choose to buy these screens from their gold mining supply store, it is not unusual at all to see lint screens, window screens, and even kitchen sifters alongside a clean-up operation. Classification screens come in many sizes: 4, 8, 12, 20, 30, 50, 100, and even smaller. These numbers represent the number of openings per linear inch. For example, a 4-mesh screen has four holes per linear inch or 16 holes per square inch, and allows material to drop through which is smaller in size than about 1/4 inch smaller, actually, because the wire in the screen takes up some of the space.
With a little practice and experimentation you will find out which screen will work the best for you and your particular clean-up operation.
Beginning Your Clean-Up
Start your clean-up by removing your concentrates from your sluice box. Next, use your #4 screen to classify and remove this spectrum of material, checking closely for nuggets and large, flat flakes. Surprisingly, many miners fail to inspect closely because they are working a deposit that only seems to produce fine gold. Nuggets can be lost because they are simply thrown out in this important stage of the process. Usually this first step is done right at the river bank, making what you must carry back to your camp less cumbersome. Now screen your materials though your #8 screen. What’s left on top of this screen will be easy and quick to pan at the river. Take what falls through the screen back to your wheel for processing.
Using Your Wheel
It is very important to go through the above steps before attempting to use your wheel to process your concentrates. Remember, the wheel works on the principles of weight, angle (pitch), and water-flow. In the following steps, you’ll be first separating the blonde sands from the heavier black sands. This process is called the “first split.”
This separation should be done using your wheel’s fastest speed if you have a variable speed wheel. This split will take a little time, but remember that if you were panning this material it would probably take as much time or more, and may not be as effective for fine gold recovery. Many people purchase a wheel to reduce the amount of panning time in their clean-up operation, as well as recovering more gold.
At this stage, you’ll want to pull the black sands and gold from the blonde sands. It’s okay if a small portion of the blondes are drawn up along with the blacks in this first split.
We have found that skimming the lighter sands off the top of the material being processed in the wheel (not in the riffles) can be more effective than allowing the tailings to simply run out of the wheel with excess water.
The best demonstration of how to use a gold wheel that I have ever seen is in Dave McCracken’s video, “Modern Gold Mining Techniques.”
When running this first split, the wheel will pack just like the riffles of a dredge. When this occurs, for better results, you can spoon material from the bottom of the wheel up onto the riffles. We also seem to get better results by spooning material onto the drier section of the wheel so that it passes into the flow of water as the wheel turns. Watch yourself very closely because this is the step where many of the larger flat flakes are lost simply by scooping the material out of the wheel too soon. Once this split is complete, you should find that you have cut your material in half or more.
Now you should have what we call salt and pepper sand and gold. If you have only black sands at this point, you have probably lost some of the finer gold already. Look closely; and if this is the case, stop, back up and rerun this split again. Remember, the wheel will only recover as well as the skill of the operator permits. So take your time and make sure you’re not losing your fines at each stage of the process.
Next, classify the remaining concentrates once more using a #12 screen. This time you’ll only have half as much material so it will go very fast. The material on top of the screen produces your bigger gold; and if you’re in good gold, you’ll be able to still see it lying all over the surface of the screen. Sometimes, I find it easier to dry and run a magnet through the sands. This approach will usually remove 50% to 80% of the magnetic black sands, leaving your gold and just a little material to pan or blow off. These gold particles and flakes should be bright and beautiful and can be put in your gold jar.
Now it’s time to tackle the material that dropped though the #12 screen by running it through the wheel. When using a variable speed wheel, this split should be processed at the slowest speed, and the pitch of the wheel should be set at a steeper angle. Use a moderate-to-slow water flow, adjusting the wheel to pull just a little black sand, and all the gold. Once you’ve run it through, simply adjust the wheel a bit steeper and rerun this gold-laden material once more, only this time just pull the gold.
This process will leave you with all your gold, and perhaps just a very small amount of fine black sand. I find that if you dry this final product, it is very easy to blow the remaining black sand of by sorting through it on a clean piece of paper and blowing gently. It is a nice way to end your day!
And finally, if you’re having any trouble in your clean-ups, remember to return to the basics by watching your classifications, checking what you’re about to discard on a regular basis, and by making sure that you’re not leaving your fine gold for someone else to recover simply by re-running your old sand piles. I hope these hints are helpful, and good luck with your future clean-ups.