BY SAM LONG

 

Dry-washing, in many ways, puts me in mind of eating at a Chinese restaurant with chopsticks. It’s fun to try; but you can’t move material from one place to another very fast, even if you’re good at it. That’s why it’s so important to pick out an area with a theoretically high concentration of gold. Of course, down here in Arizona, you’ve got about as much chance of finding an area like that as a one legged man’s got at winning a kicking contest!

That’s not to say you shouldn’t try. I always do so with this theory in mind: Billions of years ago, when God was putting tons of gold in Alaska, South America, Russia, Australia, the Yukon, and even California, he accidentally spilled a couple of pounds over Arizona. I always think of that after I’ve worked through a pile of rocks and sand big enough to shade an elephant, and not come up with enough gold to fill a tooth. All the expert mining techniques in the world won’t come up with a speck of gold where there’s none to begin with. So, the place to start is history.

I know you’ve read it a thousand times. Now you can say you’ve read it over a thousand times: It’s usually better to begin your search for gold in an area that has produced it in the past. The more the better.

From that point, go to maps. Study them religiously. I take my topographical maps to an office supply that has an enlarging copier. I have the section I’m interested in blown up two or three times. This really helps in seeing all the side washes, forks, bends, and places of slowing water that are the obvious holding spots for gold.

Now, you’re ready to hike to these areas. Of course, on your way to and from these spots, keep your eye open for any likely looking area you might have overlooked on your map. There are a zillion of them, so you’ve got to learn to be very selective.

Remember, you want to shovel rocks, sand, and gold through your dry-washer, not just rocks and sand. It doesn’t matter to your shovel. It doesn’t matter to your neighbor. It only matters to you. Take your best shot before you ever crank up your machine, and you won’t have to deal with the disappointment of getting skunked.

And, just how do you do this? Sampling. That’s right— sample, sample, sample. If you’re diligent about it, and do it correctly, when you finally start dry-washing, your question won’t be will I find gold? It will be how much will I find?

Starting up your dry-washer in a likely-looking spot without sampling, makes about as much sense as a dog barking at a knothole. Sure, sampling is a lot of extra work and it takes time. But, when it’s all said and done, you’ll end up with some gold along with the new blisters–instead of a sour attitude and the new blisters.

This isn’t to say you can’t set up anywhere and get some color. But to my way of thinking, that would be pure luck; and I haven’t experienced enough of that to feel qualified to write about it. If you have, and can make it work time and time again, I’d sure be willing to learn.

So, here we are in a gold producing area, walking up a wash that had some likely-looking gold-holding spots on our map. How do we sample? Well, as with most things, there is more than one way to skin a cat. I use a Goldspear. It’s proven itself to me to be an accurate, time saving, prospecting tool. I know lots of folks don’t think much of them, but usually they haven’t ever owned one, or don’t understand how to use them to their advantage. Granted, they’re not some super tool that can automatically find gold. But used correctly, they can sure save you a lot of needless digging. And, at the price of shovels these days, you don’t want to wear out any more than necessary.

For now though, I’ll skip the use of the spear and explain a few points of how I sample without one. Again, this isn’t the only way to sample or dry-wash, but it works for me. Adapt it to your own personality and tools, as you see fit. In my pack, my basic tools are: Two pans, a small kitchen sieve; and, because we’re prospecting dry washes, a wide-mouth plastic gallon jar of water. Needless to say, never go anywhere without your rock pick.

With these basic tools, slowly work your way up the wash, visually sampling as you go. In your mind’s eye, continually look for the places gold is likely to accumulate. The more of these types of places you can recognize, the more success you’ll have in sampling.

Likely gold-holding areas would be the inside of sharp bends; areas where the wash levels and widens, indicating slowing water; areas of red and blue clay; pockets of iron pebbles, which show the water’s inability to carry heavier minerals; or a zone of magnetite, hematite or quartz. All these are good visual indicators that gold will likely be present.

After finding a place containing as many positive indicators as possible, roll over the biggest boulder you can in that area; and using one pan to hold the water, screen some material from under the boulder into the other pan and go to work. If you’ve done your homework right, this should yield you a few colors. Jot down how many on your map at the place where you found them. If more than just a few colors materialize, try a couple more pans before moving on. Continue in this manner for the rest of the day. You should have a few different areas that are somewhat better than the others.

Now that you’ve picked a good spot to work, and packed in all your equipment, the last important point is the speed at which you run the material through your dry-washer. It’s a big temptation to drop your riffle board too low so you can process material faster. But by doing this, you’ll lose a lot of finer-sized gold. As you either know, or will soon find out, most gold in the dry washes is very small. Unless you keep your riffle board only slightly lower than level, a good portion of the fine gold won’t have time to settle. It will end up going over the end instead. You can’t feed any more material in than is going out, so be careful not to overfeed the hopper. Otherwise, you’ll end up with gold in your tailing pile. Nothing will make you feel ankle high to a frog in a post hole quicker than your neighbor coming by, to run his Goldspear through your tailing pile, and getting enough beeps to make a liar out of you, when you tell him you were planning to run it through again a second time anyway.

The biggest hindrances to running your machine are laziness and rain. If you’re the type who does more spitting on the handle than shoveling, you’ll probably welcome the rain. If not, the folks around you will surely think you were raised on sour milk. It takes the fun out of dry-washing when you just get going good, then it rains and stops your operation. That’s what happened to us this winter. With my Keene dry-washer, I could work wetter dirt than everyone else because it blows hot air. But after the fourth cloudburst, it was even too wet for me. We switched it to a re-circulating water system and kept going.

So, if you pick the right spot and don’t push your machine, you’ll get some good gold. It might not be the most gold you’ll ever get in a day, but that desert-gold is some of the prettiest you’ll ever find. Since gold is more ornamental than useful anyway, you ought to be happier than a fly in a raisin pie

 

By Jimmy Sierra

“What goes on in that metal box may be a mystery to most of us, but we all know it isn’t magic”

 

Metal detectingThe title of this article can mean different things to different people and thereby add to the mystique surrounding the entire field of metal detecting, for that is what “Electronic Treasure Hunting” is all about. The word electronic should mean the same to everyone. What goes on in that metal box may be a mystery to most of us, but we all know it isn’t magic.

The vast assortment of transistors, resistors, capacitors and various integrated circuits add up to a very sophisticated type of transmitter which broadcasts a signal through the transmitting coil of copper wire contained in the disc or loop at the front-end of the detector. This signal is affected by the electromagnetic field which is present around all metal objects. Thus, when it returns to the receiver-coil in the loop, this signal is changed. The change is interpreted by the complex circuitry in the detector box and lets us know that there is metal out there.

Depending upon the sophistication of the detector, this data can include the possible type of metal, depth of the item and even the shape or identity of the metal object. This may be an over-simplification of what goes on, but we need not worry about how it happens. Let the engineers who invent these devices handle that. The thing to remember is, metal detectors find metal. There are variables that create differences between detectors, and these variables will determine which style of detector is best-suited to the type of treasure hunting that we wish to do.

This brings us to the second part of the title of this article: Treasure Hunting. As I mentioned, this is the part that means different things to different people. To some, it means looking for dropped coins or jewelry in various places such as parks, playgrounds, backyards, beaches, picnic grounds or even old ghost towns. The locations change and the technique for searching varies a great deal, but the basic function of the detector to locate metal is the same. Some consider treasure hunting to be locating caches of buried coins or valuables, even sunken galleons. Again, the treasure and the location change, but the detector is still operated as it is de- signed, to locate metal objects.

To others, treasure hunting takes the form of searching old battle sites or ghost towns for relics of days gone by.

And yet, another select group of treasure hunters who call themselves “prospectors” direct their search for the elusive nuggets of gold, long sought by man to be used as a measure of wealth.

By now I hope it has become apparent that the common denominator linking most treasure hunters together is the electronic metal detector. The location may change and the targets may differ, but all respond to the initial function of the detector to find metal. It is only necessary to vary where we look, and to some degree, develop special skills unique to each type of treasure in order to change from coin shooter to cache hunter to relic hunter to prospector.

This might be a good time to clear up one particular misconception, one that has been brought to my attention hundreds of times over the years by those unfamiliar with treasure hunting. That is, the idea that metal detectors cannot find GOLD. This stems from some misunderstanding about the nature of gold. When I have questioned these people, I have found that most were not really sure if gold was a metal or not. Some had a vague idea that gold might be classed as a mineral. Most, however, were not sure what the difference was between a metal and a mineral.

In brief, the difference between a mineral and a metal is that a mineral is a chemical compound of more than one element, and a metal exists in its pure state as a single element. So, let’s just accept the fact that iron, copper, lead, silver, and GOLD are all metals and can be found free in that form, and that all of them can be located with a metal detector. We can surely begin to see why such mystery surrounds gold and gold prospecting, as well as treasure hunting in general.

I do not mean to imply that electronic treasure hunting or prospecting is as easy as falling off a log; only that it is not magic, and that the skills acquired while learning to hunt coins in a park with a detector are the same skills used when prospecting for gold nuggets in the Mohave Desert. The target and the location change, but the basic skill is only varied by the different types of hunting.

Up until several years ago, one of our most successful coin shooters from the Sacramento area in California had never seen a gold nugget except at the various gold shows where suction dredgers show off the treasures which they find at the bottom of streams and rivers. He had acquired the necessary skills over the years in the operation of his detector. He had learned to utilize the ability of his detector to cancel-out the ground mineralization caused by iron ore and salts which mask the ability to locate metal objects such as coins. He had trained his ear and slow searching techniques to hear those deep older coins. When he decided to give a shot to gold prospecting, he had little else to learn. He was successful right from the start. Of course, he didn’t look for the nuggets in the local park. But, he did find his first nugget in a dry streambed not more than 15 minutes from his house. He was bitten by the gold bug on that first day and will never be the same!

His biggest problem was to find a good place to hunt. He rightly concluded that the best place to start was where the old 49ers had found gold. If it was there then, it was surely there today. He was right. He began by going over the tailings left behind by old-timers. Gold was plentiful and the old methods of recovery were not perfect. Carelessness and lack of skill left plenty behind. He researched old maps and history books to seek out previous diggings. Sometimes, he went over old tailings. Other times, he searched dry washes and gulches near the diggings. Experience sharpened his skill and techniques, just as those many hours spent in the old parks had prepared him for this new approach to treasure hunting.

Averaging three days per week searching, he found more than 40 ounces of gold last year!

I do not want to paint too rosy of a picture here. The fellow mentioned above is a real experienced detectorist. He spends time hunting and looks for the right spots. Few of us will measure up to his success. But most who try their hand at treasure hunting will be pleasantly surprised at how fast they can become skilled in the use of this electronic device. Practice and patience are all that are required. Skill in tuning and operating the detector comes from reading the manual carefully and asking information from the dealer that sold the unit. Other users are a good source for acquiring special helps in learning to use the unit. I, as well as others, have written articles and books explaining in detail the tuning and searching techniques of metal detecting.

Joining up with others in a Club or association will gain you very valuable access to experience and places to hunt for golden treasure.

One of the unpredictable ingredients in the creation of a successful treasure hunter is LUCK!! The old adage that you have to be standing over a target to find it, is true. My friend and I were searching an old baseball field a number of years ago which was adjacent to an old Mission. We both found numerous coins, many silver, but all from this century. I was lucky enough, however, to find a 1778 Spanish half real dating back to the Mission Period. It was only 4 1/2 inches or so deep. It was luck. I was practicing the same learned skills as my partner and we both were successful. My old coin was there because I was standing over it.

I have a good friend with whom I prospect. We dig a lot of targets in order to find the elusive gold nugget. I have found many nuggets, most in the tiny-to-small size-range, but none really large. However, along with many smaller nuggets, this fellow has found a 6-ounce, a 9-ounce, and a 12-ounce piece of Mother Nature’s natural golden treasure. Granted, he hunts for gold nuggets a lot more than I do, but many who hunt as often as he does never find nuggets in that class. Wouldn’t you say some luck came his way? Each one of these nuggets was found with a different make and model of detector.

Many detectors are pretty equivalent in ability to find metal, but all metal detector users are not equal in skill — or in luck.

Another example comes to mind at this time: This one might seem pretty far-fetched, but it is true. A few months ago, a prospector-friend of mine called to announce that he had just found his largest nugget to date. It was a ¾-ounce piece, that’s 15 pennyweight. Now, that is a respectable nugget. Of course, he said he found it with the help of his faithful dog. You might call the dog his gold-hound at this point. While my friend was prospecting along the bank of a popular river, his dog was doing his duty near the water. As he noticed his dog scratching at the sandy shore, he caught a glimpse of something flashing in the sunlight. He went closer to investigate and spotted the aforementioned nugget with loop and all attached. Some luckless prospector had lost his prized specimen from around his neck. One man’s loss is another man’s gain, as they say. It goes without mention that this is one dog that will never want for attention again!

We have talked about learning how to use the detector, regardless of what the object of your search is. There is no substitute for expertise and skill. We have mentioned that buying the proper detector is essential and we have pointed out that a certain amount of good luck doesn’t hurt. The final ingredient is good old perseverance and perspiration.

My basic intent in this article is to clear away some of the magic from electronic metal detecting and show it as an acquired skill, which is what it really is. It is important to buy the best detector you can; one that has the ability to cancel the ground-mineralization. This is most important if you plan to use the detector for prospecting, because gold and silver are most-often found in highly-mineralized soil.

If you are going to use the detector in trashy areas (lots of man-made metal objects), you should buy a detector that has some ability to identify trash. Otherwise, you will have to dig every target that sounds off. This is not only tiring; but since you can only dig so many targets in a day, it diminishes the odds of digging good targets. You can see that this would not be important if you were relic hunting, where all items are potential treasures. But it is more important when coin hunting, where pull tabs and bottle caps are not desired, or in prospecting, where nails and tin cans left from former miners are tedious to dig and not as valuable as gold nuggets. Of course, if the area is virgin, one would not have a need for identifying trash.

Being able to identify a “hot rock” (a rock with different mineral content than the surrounding terrain) is also an important feature to be looked for in a detector to be used for prospecting. Have your dealer help you pick a detector best-suited for your needs, whether they be specialized or multi-purposed.

Good Hunting!

 
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By Dave McCracken

Always set up a dry-washer downwind of where you are working!

Dave Mack

 

Deserts consist of huge deposits of sedimentary material which have been affected by ancient ocean tides, ancient rivers, glaciers, floods, gully washers and windstorms. They are literally a gold mine of placer deposits.

There is also an enormous amount of gold-bearing mountainous dry placer ground which has remained relatively untouched by large-scale gold mining activity because of the scarcity of water required in those locations to support wet recovery methods.

Generally speaking, dry methods of gold recovery are not as effective or as fast as wet recovery methods. Yet, dry methods do work well enough that they can produce gold well if the ground is rich enough. Recent developments in dry washing equipment have made it possible for a one or two-man operation to work larger volumes of dry placer ground without water, and obtain good results in gold recovery.

Dry processing recovery systems generally use air flows to do the same job that water does in wet recovery systems. Under controlled conditions, air flows and mechanical motion and vibration can be made to effectively get rid of lighter, worthless materials. This causes a concentration of heavier materials similar to what occurs in wet processing.

SETTING UP TO WORK AN AREA

Sometimes a road can be bulldozed to your spot. Sometimes you can drive right in with a 2 or 4-wheel drive truck. In these situations, you might consider screening pay-dirt into the back of a truck and hauling it to a wash plant to be processed elsewhere. Actually, this is just slightly more difficult than shoveling directly into a wash plant. The hardest part is breaking the material away from the streambed and classifying it. It takes a little more time to haul the material to the wash plant, but that depends upon the distance and the condition of the road. It is also more difficult to shovel up into a truck. Some small operations use a portable conveyor belt to lift the material into their truck. Feeding the material from a truck into a wash plant is not as difficult, because it is usually down hill. An average one or two-person team should be able to move the equivalent of a pickup-sized load of screened pay-dirt and process it through a wash plant at another location in the period of a full day’s work-perhaps even two truckloads, depending upon the distances involved. If the material is paying well, they could do well at it, too.

DRY-WASHING PLANTS

If conditions do not allow you to truck the pay-dirt to a nearby water site to be processed by wet methods, you will have to consider processing the rich material by dry-production methods.

While dry-panning and winnowing do work, and have been broadly used as a means of production during the past, they are not normally as effective as some of the modern dry-washing plants which are available on today’s market.

Dry-washing machines use an air blowing fan or bellows-type device to blow a controlled amount of air-flow up through the dry material that is being processed. Air flows help blow off the lighter materials and allow the heaviest particles and gold to collect.

Dry-washing plants are available which can either be operated by hand or by lightweight engine and air-fan assemblies.

“Non-motorized dry-washing unit”

A hand-operated dry washing plant usually includes its own classification screen as part of the unit. Raw material can be shoveled directly onto it. The bellows air-blower is usually operated by turning a hand crank, which is often conveniently located so that one person can both shovel and alternately work the bellows at the same time. Under ideal conditions, two people working together can process up to a half-ton of gravel per hour by taking turns, one person shoveling while the other works the bellows.

Some units also have a 12-volt electric conversion kit to allow you the option to either hand-crank in the field or connect to a 12-volt battery for automatic bellows operation.

Various gasoline motor-driven dry concentrating units are available on the market which utilize static electricity and high-frequency vibration to help with gold recovery. Most commonly, there is a high-powered air-fan which pumps air through a discharge hose into the concentrator’s recovery system. The air currents which pass through the recovery system are adjustable so that the proper amount of flow of lighter materials through the recovery system can be obtained-similar to a sluice box in wet-processing. The purpose of the steady airflow is to “float off” the lighter materials through the box. Heavier materials like gold will have too much weight to be swept through the recovery system by the flow of air.

The bottom matting in this type of concentrator is usually made up of a specialized material which creates an electrostatic charge as high velocity air is passed through it from the air discharge hose. Fine pieces of gold, while not magnetic, do tend to be attracted to surfaces which have been electrostatically-charged, similar to the way iron particles are attracted to a magnet. So the bottom matting in these concentrators often attract fine particles gold to itself and tends to hold them there.

Some motorized dry concentrators also use a high-frequency vibrating device to keep the entire recovery system in continuous vibration while in operation. The way to get gold particles to settle quickly down through other lighter materials is to put the materials into a state of suspension. The vibrating device on this concentrator helps fine particles of gold work their way down through lighter materials that are being suspended by air-flows.

Here follows an excellent video demonstration which shows exactly how motorized dry concentrators work:

A motorized dry-washing machine is excellent for the production demands of a one or two-person operation. Under ideal conditions, it is able to process up to about a ton of raw material per hour, which is the equivalent of what a medium-sized wet sluicing operation can produce. This is as much or more than one or two people can usually shovel at production speed when working compacted streambed material. Most motorized dry-washers do their own screening of materials and almost everything else automatically. This leaves the operator free to produce at his or her own comfortable speed.

Total weight of the average motorized dry-washer is about 75 pounds, but the units do break down into separate pieces which can usually be carried around by a single person. So the electrostatic concentrator can be carried to a hot spot if it is worth a few trips to do so. They usually get about 3 hours to the gallon of gasoline.

SETTING UP A DRY-WASHER

There is no fixed formula for setting up the proper air flows and downward pitch on the recovery system of a dry-washer. A lot depends upon the nature of the material that you are processing, how heavy it is, whether or not the material is angular or water-worn and the purity (specific gravity) and size of the gold being recovered. Each of these variables is likely to affect how you must set your recovery system in each different place that it is operated.

The main thing to remember is that the machine needs to separate the gold from the lighter, valueless materials. If you only have a small amount of air-flow running through your dry-washer, then you will need more pitch on the recovery system-and you may need to feed the material slower. Too much air flow can also be a problem. Normally, you would compensate by adjusting to a lesser pitch on the riffle board.

Watch how the material flows over the riffle board. You should see the dirt rise up in an orderly fashion and flow over top of each riffle. It looks an awful lot like water. It is best to keep a steady feed of material going through a dry-washer at all times. The riffles should be filled about half to three-quarters, with a steady flow moving from one riffle to the next. The material in the riffles should have a fluid look to them; they should not be packed solid.

This following very important video sequence demonstrates how to set up and operate a motorized dry-washer, and it shows exactly what you should look for while making flow adjustments to obtain optimum gold recovery:

It is a good idea to shovel lower-grade material into your dry-washer while adjusting for the proper air flows and pitch. Once set, you can shovel in the pay-dirt.

One thing about dry-washing is that because it is generally slower than wet methods, the pay-dirt must have more gold. High-grade areas in the deserts certainly do exist! This is all the more reason to make sure your recovery system is set properly before processing pay-dirt. Chances are that you will not see any gold that might be discharged into the tailing pile through a dry-washer recovery system.

Another thing about setting up a dry-washing production program is that you always set up a dry-washer downwind of where you are working!

Once gold falls into the dead air space within the riffles, it will usually stay there. The air-flows are generally not strong enough to push gold out of there. There is a limit to this, however. Just like a water recovery system, a dry-washer will concentrate the heaviest materials which it processes. After some time, the heavier concentrates may require stronger air flows or a steeper pitch to keep them in suspension. At this point, it is probably time to clean up the recovery system and start all over again. If you are keeping a close eye on your recovery system, you can see when it is time to clean up. The fluidity of the material inside the riffles becomes more concentrated and slows down.

DRY-WASHING AND CLAY-LIKE MATERIALS

Material to be processed must be thoroughly dry to get the best results out of any dry-washing plant. Sometimes you will run into moist clays when out in the dry regions-just like you do in the wet streambed areas. It is also possible to find a pay-layer associated with the clay. Clays make dry-washing procedure more difficult, because they must be thoroughly dried out and broken up before being processed effectively by dry methods.

Sometimes this means the material needs to be set out in the sun to dry for a full day or more before anything further can be done with it. Sometimes it is necessary to dig clay a couple of days ahead of the processing stage. You can alternate spending a day digging and laying out material to dry, and then a day processing dried material. Sometimes, the dried clay can harden into clumps, which then must be broken down into dust and sand before you can recover the gold out of it. When necessary, all of these requirements require more time and energy. But if a good pay-streak is involved, you will find yourself doing whatever is necessary to recover the gold out of it.

It may be necessary to use rock-crushing machinery to break up hardened clay-like material and crush it down on any kind of a production -scale.

The clean-up of concentrates from a dry-washing plant is accomplished best by wet-processing methods. Usually, if you have room-enough to haul around a dry-washing plant in your vehicle, you will also have room for enough water to pan down your final concentrates, too. The following video sequence demonstrates how and when to perform a final clean-up during dry-washing:

If water is not available to you out in the field, the clean-up of your dry concentrates can sometimes be accomplished quite effectively by running them through your dry-washing plant several times. Final cleanup procedures can then be done to separate the gold from the last bit of remaining valueless material.

DESERT PLACER GEOLOGY

The chances of finding a hotspot out in the desert, or in some other dry region, are probably just as good or as your chances of finding a hotspot in the watersheds of the gold-bearing mountainous areas. These chances are pretty good, providing that you are willing to spend the time, study and work that is necessary to implement a good sampling plan.

Probably your best bet is to start off with a “Where to Find Gold” book and study the geological reports which apply to the area(s) of your interest. There has been some small-scale mining activity out in the dry regions. Much of it was lode mining, but some placer activity took place, as well. A good portion of prior activity is recorded information today. It can be of great value to you to know where gold has already been found. It is almost a sure thing that the areas which were once worked for gold at a profit were not entirely worked out. They might be worked again with today’s modern equipment at a profit. Any area which has once proven to pay in gold values is a good generalized area to do some sampling activity to see if additional pay-dirt can be found.

The desert areas were pretty-much left alone by the large-scale mining activities of earlier times because of the accessibility problem. Often, during earlier times, there was not enough water to sustain life, much less to process gold-bearing material.

But desert prospector should not limit him or herself to only the once-proven areas. Most of the desert regions have gone pretty-much untouched by past (effective) sampling activity because of accessibility problems, lack of water, and not having adequate equipment to do the job up until recent years. So the desert prospector has access to a lot of ground, and there are not that many competitors to worry about.

A single large rain or wind storm can change the entire face of the desert in just a few hours. There is very little undergrowth in these areas to prevent a good-sized rain storm from causing an incredible amount of erosion. And so you hear all the old-timers’ stories of finding bonanza-sized gold deposits, marking their position, going out after tools and supplies, and then returning to find the desert entirely changed and the bonanza apparently gone. Undoubtedly, some of these treasure stories are true. After all, many of those old-timers had gold to go along with their stories. Many of them spent the rest of their lives looking for their “lost gold mine.”

All of the placer geology concerning wet areas also applies to desert placer deposits (most which were developed during wet storm events). The same remains true of eluvial deposits-which is the gold that has weathered from a lode and been swept some distance away by the forces of nature. Eluvial deposits in the deserts (called “Bajada placers”) tend to spread out much more widely, and in different directions. This is because they are usually not eroding down the side of a steep mountainous slope. Therefore, they are sometimes a little more difficult to trace back to their original lodes. But it can be done. The answer is to do lots of sampling.

History has shown that one of the best locations to look for gold is where the hills meet the desert and fan out. This is where the water slows down during flood storms and drops gold in the gullies and washes. There also are likely to be more gold traps further up the hillside.

When doing generalized sampling in the desert, concentrate much of your activities in the washed-out areas, where natural erosion has cut through the sediments and created a concentration of heavier materials. Dry-washes, dry streambeds and canyons are good for this. Get an eye for the terrain, looking over the high points and the low points to get an idea of where the water flows during large flood storms. Areas where the greatest amount of erosion has taken place are areas where the highest concentration of gold values might be found. Remember that we are looking at many thousands of years of erosive impacts.

Bedrock will be exposed in some low areas, as in canyons and dry washes. These are ideal places for you to get into the lowest stratum of material-where the largest concentrations of gold values are often found. Large and small canyons have been formed by many years of erosion and are likely spots to find paying quantities of gold.

Caliche is cement-like false bedrock which is commonly found in desert placer areas.(photo USGS)

The desert and dry areas also commonly have a “false bedrock” layer specifically called “caliche.” Sometimes (often), this caliche layer is only a foot or two thick. In some areas, gold is concentrated along the caliche, just like on top of bedrock.

After a storm in the desert, in some places you can find small pockets of gold in the gravel traps, under rocks and under boulders which rest on top of the caliche. Sometimes the gold is pounded directly into the caliche and needs to be removed with a pick or crevice tool. Caliche layers which are close to the surface allow small-scale dry-washing operations to be economically feasible, because of the lesser amount of gravel and material which needs to be shoveled off the gold deposits.

Streambed material can be recognized by the smooth water-worn rocks. Anywhere in gold country, where streambed material is present, is a prime area to be doing some preliminary sampling. Such material indicates that it has been exposed to a substantial amount of running water. This means concentrating activity took place with those same materials. It is possible that the material was once washed out of an ancient river.

However, gravel and material does not need to be water-worn to carry gold in the desert areas. Rough and angular gravel, which has not been greatly affected by water, also sometimes carries gold in volume amounts. Testing is the key.

Sometimes it can be worthwhile to do some sampling in the different layers of desert material when they are present and exposed. Gold concentrations in and between flood layers can happen even more in the desert. This is because of the flash floods which can occur there.

Sometimes substantial gold concentrations can be found just beneath boulders which rest upon bedrock, or up in a layer above bedrock.

When you find a gold deposit in a dry area, whether on bedrock or the caliche, you will want to thoroughly clean the underlying surface upon which the gold is resting. Seldom will you visually see gold in dry placer material-even when there is a lot of gold present. Use a whisk broom or vack machine to clean all of the loose material. Sometimes, it is also productive to break up the surface of the caliche or bedrock with a pick or other crevicing tool.

Occasionally, in dry washes, you can actually see stringers of black sand along the bedrock or caliche-especially directly after a storm. You can sometimes do exceptionally well by following these stringers and digging out the concentrated gravel traps. Do not forget to test the roots from trees and other vegetation in such areas. Vegetation requires a certain amount of mineralization to grow. Roots can grow in and around high-grade gold deposits. I have heard of single roots which have been dug up and produced as much as three ounces of gold!

Some electronic prospectors use their metal detectors to trace concentrations of black sand. Then they follow up by testing the areas which produce the strongest reads from their detectors.

Some desert areas, like Quartzsite, Arizona, also have gold just lying around anywhere-even on top of the ground. Such places are excellent for electronic prospecting and dry-washing. The deserts of Australia are famous for this. I have a number of friends who have been very successful in the Nevada deserts, using metal detectors to recover large numbers of nuggets, some very large, directly off the surface of dry desert ground.

If you find a piece of gold on the surface of a dry placer area, it is likely that there are more pieces of gold in the immediate area. Electronic prospectors call these areas “patches.” Gold generally does not travel alone-unless it was dropped there by mistake.

Sand dunes in the desert are usually not very productive. This is because they mainly consist of lighter-weight sands that were deposited there by the wind. However, sometimes the wind can blow off the lighter-weight sands from a particular location, leaving the heavier materials exposed behind. This is similar to what happens after a big storm at the gold beaches. This is something that should be watched for.

When prospecting around in the dry areas, when you encounter tailing piles from past dry-washing operations, it might be worthwhile to do some raking of the tailings and scan around with a metal detector. Sometimes old tailing piles can be productive enough to run them through a modern dry-washer.

 

 

By Linda Haze Gabris

 

Gold nugget found while metal detectingI first wanted one when I read about a million-dollar nugget found in Australia by an electronic-prospector.” The captivating article told about an enormous lump of gold that was unearthed by a miner using a metal detector. Several stories later, one of these devices was on my “have-to-have” list. That was years ago. In 1988 I ordered an A3B-United States Garrett Gold Hunter.

My owner’s manual promised this unique instrument would help make all of my dreams come true! Well, here I am more then a decade later with good news. I can vouch for the fact; these strange-looking gadgets really do work! During these years I have unearthed some of the best treasures to be found anywhere in the country!

First of all, an “electronic-prospector” has to redefine the word “treasure.” To me, a treasure is almost anything that lies hidden and secured by earth or water.

While there is no thrill quite as great as finding a lustrous gold nugget wedged in a crevice of bedrock, or an old coin buried deep in pine needles along the trail, one can learn to appreciate other “finds,” too! “Beeping-out” and digging up simple objects like an old tobacco tin, a horse shoe or the remains of an enamel wash dish also contribute to my own “joy of the hunt.” A heap of old rusty cans behind a tumbled miners cabin, or a scrap of metal embedded in a gravel bar, offer reminders of those who traveled ahead of us-down the golden trail. Some hunters call these items “bad beeps.” I have learned to appreciate them as interesting bits of yesterday!

The first thing to do when learning how to operate a metal detector is to read all of the manufacturer’s literature. Make yourself familiar with the features of the model that you have chosen. You will receive maximum performance from your detector by studying its manual. Even if it takes days, I suggest you don’t hit the gold fields until you understand all of your detector’s functions and features.

When you head for the hills, make certain that you bring along a spare set of batteries!

The best place to get familiar with your new machine is in a “salted” area near home. Make sure you pick a place where you will not encounter buried power lines! You can build a test plot by planting several items at various depths, from two to ten inches deep, and about two feet apart.

Using bits of colored cloths tied to little sticks, you can flag the location of the different items; a nail, ball of tin foil, bottle cap, an old fork or spoon, a couple of coins, and a gold nugget or ring (be sure to mark the location well). Note the depth at which they were buried! Now you can scan the targets and listen to the detector “beeping out” its signals. If you listen closely, you will hear different tones for each metal.

Once you can tell the difference between the sounds, study the sounds in accordance with the depths. This adds a challenging twist to your learning curve!

Using lots of patience, try hunting for items in both the “all-metal,” and “discriminate” modes. You will want to wear headphones for greatest effect. Following your manual, try both automatic and manual tuning. Work with the instrument until you understand its unique workings. Practice, as you would with a guitar, until your detector is “tuned.” After you are familiar with all your model’s features, and you know what the different types of targets sound like, you can head into the hills with confidence and great expectations!

I find the equipment needed for electronic prospecting is very simple. You will need a tool for digging out the “buried treasures” as you discover them. I use a long, narrow-mouthed spoon in areas where the earth is soft. In areas of harder soil or cemented gravel, I find a sharp-nosed pry bar works best. If I am detecting for gold in gold producing regions, I always carry a plastic gold pan and miner’s shovel. When beeping occurs in gold-bearing gravel, I shovel the “scanned-over” dirt into the pan, and then run the detector over the pan to see if I scooped up the target; or if it is still in the ground.

Once I have the target in the pan, I sift or pan out the material to see what is reading out on my detector. Don’t use a metal pan, because you won’t be able to pin-point the target.

Don’t be disheartened if most finds only pan-out as old sluice box nails or rusty bits of metal. This is to be expected in some areas. Determination and patience will eventually lead you to precious golden nuggets for your poke! You will need a leather pouch or plastic container with a tight-fitting lid to put your new-found gold in. Zip-lock bags are also good for this.

I always carry all “dug-targets” back to camp with me, so that the search area will be fresh for my next hunt (or for other detectorists!)

When a nugget has been unearthed, I usually turn off my machine and hand-work the area by test-panning surrounding gravel that could (often does!) contain particles of gold or other nuggets too small or deep for detection. Until you know the full range of your model, this is a good practice to follow. All detectors have varying ranges of depth penetration!

I have discovered the most productive areas for metal detecting gold are in the areas around old workings. Some of my most prized nuggets have been “beeped” out of tailing piles left behind by the old-timers!

I have also unearthed nice nuggets from the “spillage” around the old recovery systems from bucket-line dredges, sluice boxes, and shakers. Using my metal detector, I have stumbled upon many clean-up” sites from big operations. A “clean-up” site is usually near water, where the heavy concentrates from an operation have been worked-down to just the gold. Concentrated material from an old recovery system contains black sand, rusty nails, bits of metals; and more often than not, a good amount of fine gold particles that were lost during the clean-up process. After my detector has sounded-out a “clean-up beep,” I pan it out before moving on.

In my years of prospecting for gold, I have not only unearthed a collection of remarkable gold nuggets, but I have also found other unique treasures. One such piece was a sad old iron that I was able to restore to good condition. This was located in a gravel bar, in the middle of the Manson, a noted gold producing river in British Columbia.

Other “treasures” include countless forks, knives, spoons, metal buttons, medals, coins, a silver-handled nail brush, and a pill box dated from the 1800’s. I have also found tons of rusty square nails, tin cans, scraps of screens, grates from old workings, and many tidbits from unknown objects.

Every target, whether it is a kidney bean-sized nugget, or a mere bean can, offers me the excitement of the dig; the thrill of discovering something that lay hidden in the earth. It is treasure; no matter how great or small! That’s what electronic prospecting is really about: The “beep” at the end of the search coil!

 

By Jude Colleen Kendrick

 

Dry washing1I remember, in my beginning days of prospecting, driving through the Upper Mojave Desert in Southern California, looking for mines to explore and tailings to scratch through. Occasionally, off to the sides of the road, I would spot small areas where dust and sand billowed up. At first, I thought that they must be “dust devils,” yet they never seemed to change position. In my imagination, I wondered if someone was sending up smoke signals, because that is what they appeared to resemble. One day, I decided to satisfy my curiosity and follow a dirt road up to the puffs of dust.

As I drove up, I saw an old man shoveling gravel into what I now know was a dry-washer. My own previous experience in gold mining had been with suction dredges, so I was excited at the possibility of another way to find gold! The gentleman was kind enough to show me how his dry-washer worked. He explained that he also dredged during the summer. But during the winter months, he headed for the more moderate desert-climates. The thought came to me that now I could prospect year-round, and that everyone in my life would really be annoyed at that. This was because I didn’t leave much time for anything else but gold prospecting, as it was!

For a more comprehensive explanation about dry-washing, please click here.

The old prospector’s machine was a “Nicks Nugget;” which, as I understand it, was constructed upon the design of an “Old Beck’s” dry-washer. It basically worked from a large bellows which was run by a small gas engine set up around 10-feet away (to separate the motor further from the dust). There was a 10-foot leather belt attached to the pulleys. I noticed that the pulleys were connected in such a way that the entire machine vibrated when the bellows opened and closed. The man told me that he would not have any dry-washer other than a Nicks Nugget I, of course, asked him where I could find one for myself. He told me, “Someone one has to die, because they are not made anymore and that’s the only way you’re ever going to buy one!” That is exactly what happened about a year later. An old prospector in the town of Randsburg passed away. I heard that his equipment was being sold and bought the Nicks Nugget!

Drywashing machineMy machine has great recovery. I have tested my tailings throughout the years; and to my knowledge, I have never lost a single speck of gold!

The desert is peaceful and quiet. At night, you can see the sky and stars in a way that is beyond words…

I should point out that dry-washing is a dirty way to prospect. No matter where you set up the machine so that the dust blows away from you, the wind figures out what you are doing. Then it changes direction so that you get a mouth-full of dust with every shovel-full of gravel! I suppose this is just one of Mother Nature’s many ways of making you pay dearly for her most cherished golden treasures!

Most of the time, I wear a bandanna, which helps a little. But when I go back to camp, I still look like “Pig-pen” from the Peanuts cartoons! Still, it has always been worth it.

Winter in the desert can be hard at times, because the temperature-changes are quite drastic. It will be a comfortable 70 or 75 degrees during the day. Then, the afternoon winds can gust up to 60 miles per hour, and the temperature can drop as low as 20-degrees during the night. I woke up one morning to find that all of my panning water was frozen solid. I could not believe it!

The desert also demands the most out of your creativity and imagination. Very often, we all forget some part of our equipment, no matter how careful we are about packing. Yet with a little thought, anything can be fixed. On one trip, I had forgotten my large panning tub, so I ended up digging a hole, lining it with a large plastic garbage bag, holding the edges down with rocks. Presto; a baby swimming pool! I used it to pan down and perform final clean-up on the concentrates from my dry-washer.

Another time, the worst possible items were forgotten; which were the legs to my dry-washer. Can you imagine? I was frantic! After a few moments of figuring my whole trip was for nothing, I looked over the poles from my picnic awning, and the light went on in my head. Shortly thereafter, I took two of the poles, broke them off at the length I needed, and punched four holes in the poles for the nuts and bolts. Within minutes, I was already cranking up the dry-washer. There is always some solution if you are in the right state of mind; you just have to find it! I’m sure this is all just a part of gold prospecting.

The beauty of the desert makes up for any discomforts which you may experience along the way. Usually, nobody is around for miles. It is peaceful and quiet. At night, you can see the sky and stars in a way that is beyond words. And the gold has always been there for me, from flour to nuggets of various sizes and shapes.

One of my favorite things to do while dry-washing is run my machine all day, collect all of the concentrates; and then at night, by lantern-light, pan everything out! There is something wonderful about working everything down to that glimmering, beautiful gold at the end of my day!

During my years of dry-washing, I have spent Christmas out in the desert a number of times. One year, I grabbed three friends (who have parents and family in other states), and took them to one of my mining claims for a “different” type of Christmas celebration. We decided we would cook our turkey on the BBQ and try to make the side dishes on the Coleman stove. A friend of mine had hooked-up an apparatus so that my rotisserie on the BBQ worked off a 12-volt battery. It was great!

My friends and I thought everything was under control until we realized we had bought too large of a turkey. So we ended up eating our Christmas turkey at 10:30 at night! By then, we had already eaten all of the side dishes as “appetizers.” After a few toasts of champagne, nobody seemed to care much about how or when the turkey was done! It was sometime during that evening that one of my friends decided to make a “snowman” out of three large round lava rocks. Even though there was no snow out there, we found ourselves making the best out of our situation. I’m certain that none of us will ever forget that Christmas experience!

Now-back to the important thing — gold! I have usually dry-wash alone; but when I do have a partner, it certainly makes things a bit easier on both of us. One person can be breaking-up the gravel while the other can shovel. During one of my trips, I ran into my friend Ed “Half-Bucket” Daugherty. So we decided to team up for a while. Later, when we realized that we were onto some good gold, he and I were both feverishly shoveling gravel into my machine so fast, that several times we crossed our shovel handles and sent gravel flying everywhere. To this day, I am convinced that it was those lost shovelfuls which had the big nuggets in them! I’ve often wondered if “Half-Bucket” ever went back out there to get them…

I once watched a young man with a whisk broom and dust pan going from one prospect hole to the next, left behind by other people. He merely swept the shelf completely clean and panned-out what he had collected. He found more gold that way than I did running yards of gravel into my dry-washer! So I started using this method, but took it a step further. I took a gas-powered vacuum, sucked up the layers left on the shelves by others, ran that material through my dry-washer, and then panned-down the concentrates. Trust me; by following this method, I have always recovered a lot of color and sometimes a small nugget or two. I nicknamed this method “dry crevicing.”

While I have not tried it yet, I have run across others in the desert who have made fantastic gold recoveries using modern metal detectors to locate pockets and “patches” of nuggets. I have this plan of trying to combine modern electronic detecting with dry-washing…

At the time of this writing, it remains a little warm to start working my mining claims in the desert. Writing about it, though, has me counting the days until the weather cools.

Until then, I’ll look at my gold from last season and imagine my bottles completely full for the next time.

But even if they aren’t full, the desert and dry-washing are wonderful for the winter months. I can’t wait! Good Luck!!

 

 

 

By Dave McCracken

Every successful gold miner will tell you he or she is absolutely willing to devote whatever time and energy is necessary to locate the next discovery!

Dave Mack

Why is it that some people are able to succeed well at gold mining on a continual basis, while others have difficulty making it work?

There are a multitude of factors which contribute to the success or failure of any operation, but there is one factor which I feel underlies all the rest. It has to do with time.

Upon close inspection, you will find that every person who is doing well in these activities, other than the occasional lucky person, has been willing to devote a great deal of time to his or her mining activities. While luck does contribute to some excellent discoveries, you will find that good luck comes around more often when you spend more time searching for gold.

Unquestionably, there are skills, techniques, and standard procedures to learn in order to succeed well in gold mining. It takes time to get through the learning curve.

People who get involved with the idea of getting rich quick are usually disappointed. People who are willing to devote whatever time is necessary to polish their skills, and who are willing to devote themselves to locating the next discovery, usually do pretty well.

And, it is not necessarily true that you need to spend a lot of time before you start making important discoveries. It is mainly the willingness to devote lots of time. We have seen many beginners, who were approaching the activity with the correct viewpoint, do very well right from the start.

Most good things in life take some time to develop. Get rich quick schemes tend to cheapen the value of an activity. More often than not, it takes time to do things the right way, to make things come out good in the end.

Older people, wise with age, often say that their most worthwhile accomplishments took lots of time and energy. And, for them, the time and energy spent was the best part of it!

There are few activities which are better, more exciting, and more rewarding than gold mining and treasure hunting. While it can be aggravating at times during the testing stages when you are not finding what you are looking for, this just makes the thrill of discovery all that much better.

Every successful gold miner will tell you he or she is absolutely willing to devote whatever time and energy is necessary to locate the next discovery. And this is a lesson we could all learn from.

 

“Shallow water dredging can be very rewarding”

 

When it comes to small-scale gold mining, disability does not mean inability. It simply means that we must make accommodations. If you want to say that you can’t do something, then you won’t be able to do it. Your disability, when it comes to mining, is a state of mind. There is a form of small-scale mining that will fit everyone.

Possibly, I have been fortunate in being able to find miners to show me how to mine. Almost everyone I have run into has been more than willing to help, but better than that, they were willing to share their knowledge with hands-on demonstrations. Using this information, I have been able to determine what accommodations I must make for my personal disabilities.

Most of us are unwilling to accept the fact that we may not be able to do something. I think those of us with disabilities may have a greater failing in this. I’m as guilty as anyone.

I started out with a pan and a couple of buckets, and then added a sluice. What I hadn’t properly learned was how to pan. With two bad shoulders and a lack of breathing capacity, the standard panning style just doesn’t work. An old miner with arthritis in his back showed me how he does it, and it works. Confidentially, I still don’t pan well, and that’s why I own a mechanical panner. The next step up was a 2 1/2-inch dredge. It breaks down into manageable loads, and I call it a “four tripper.” Four trips for me to get it in or out of an area.

Keep in mind that miners are a friendly and helpful group. If you are having trouble moving equipment, then ask for help, but I’ll bet you are offered help before you ask. Don’t let anyone kid you, shallow water dredging can be very rewarding. You may not be pulling an ounce a day, but what’s wrong with a couple pennyweight? Also don’t forget that at the end of the day you are going to have to do something with the concentrates you have produced during the day. They weigh twice as much at the end of the day when you are carrying them to your vehicle.

The biggest mistake I made was to let my desire to move more material overtake my common sense. I bought a 4-inch dredge. It became a six-plus tripper. After putting it in the water twice, being exhausted each time, and having friends become very concerned when they watched me move the loads, I have given up on that idea. I’m now back to the 2 1/2-incher. I recently saw in a magazine article a listing of what the author felt was the minimum dredge set-up to start out. He felt that a 4″ dredge was the best, and this included air. I won’t argue too much, but my concern is really with the many miners who begin using air without training. For the person with a heart or lung problem, the compressed air could be a killer.

Another alternative to consider is having a partner. It can be your wife, girlfriend, or just a friend. This way you can share the equipment-moving chores, and you can complement each other when it comes to the mining. If nothing else, someone has to carry the drink cooler and be “straw boss.”

Small-scale gold mining can be good exercise, but know your limits. Have a talk with your doctor to see if there may be a change in your medication due to exercise or altitude. My medications do change when I’m on the river. Your doctor will probably look at you like you are crazy when you say gold mining. Just show the doctor some of the gold you have found. You may end up with the Doc on the river, too!

 

BY MARCIE STUMPF/FOLEY

There is a fairly new method of mining out there in the mining community that is rapidly gaining in popularity, with good reason. It is called “Vacking;” and, as you might suppose, involves vacuuming material.

As a suction dredge vacuums material from the bottom of the river, this is a type of dry-land dredging. It involves using a small, lightweight unit to vacuum cracks and crevices of exposed bedrock, moss on exposed bedrock or boulders, or material in a dry wash in the desert. For this “dry land dredging,” however, there are no uncomfortable and expensive wet-suits to don, no heavy equipment to carry and then set up, and no long period of learning how to operate the equipment, or learning where to find gold.

Anyone who is familiar with mining knows that there is a much larger proportion of fine gold deposited than large gold, in almost any area. Each winter, as the rivers swell with winter rains and snows, much fine gold is washed down them. The fine gold, since it is much lighter in weight, is deposited much higher on the banks, or in the material of the river. As the high waters recede with the onset of spring and summer, much of the areas where the fine gold is deposited is left exposed up on the banks of the rivers.

The new units consist of a two-cycle gasoline engine mounted on a five gallon container, which is equipped with a suction hose and a crevice nozzle. They are very efficient at pulling the fine gold from moss, and at cleaning out crevices. Previous efforts to accomplish this by hand were slow and painstaking, and not very efficient. Collecting fine gold has always been one of the greatest challenges facing any miner, and some people spend years attempting to perfect their fine gold recovery.

Not only does “vacking” do an excellent job at recovering fine gold — it is a lot of fun! It is so fast, simple, and easy to use, that it seems to take all the work out of mining. You are still out in the great outdoors, still getting healthy exercise, but all that’s left when you remove the excess work is the fun.

Since we live and work very near a gold-bearing river, if my husband can squeeze two hours of time, he can get to his favorite spot, set up, get in most of that time mining; and still come home with enough gold to feel he has been mining. If he is dredging, that’s not enough time to more than set up and get started before he has to quit!

These units come on their own back-pack frame, and all accessories are carried right inside the unit. It is a completely self-contained unit, and includes an extra fuel bottle, a crevice tool, a gold pan, a “sniffer bottle” to remove the gold from the pan, and even a sample vial to keep it in. With all these accessories, the unit weighs just 15 lbs., so you could hike into the back country with it without undue strain.

Many wives who are not interested in dredging or motorized sluicing (high-banking) enjoy using this type of unit because it is something they can do completely on their own. The only problem we have seen develop is that when some of the husbands see that the gold recovery exceeds that of their dredge or motorized sluice, they want to use one also. Then, they either fight over the one unit, or join the growing group of “two-vack” families. Since they are such low-cost units, this is pretty easy to do.

I recently talked to one avid vack-miner who has been using one of these units for two years. He was concerned that he might possibly lose some of the fine gold out the exhaust as the unit filled, since it is so lightweight. Shortly after purchasing his unit, he fitted an elbow and extension over the exhaust, and directed it into a container of water. He has used it faithfully, and panned out the light powder that accumulated each time. He has never found even a speck of gold in it.

A crack or crevice in exposed bedrock that runs crossways to the current of the river acts as a natural riffle, catching fine gold just as the riffles of a sluice do. The moss that accumulates on exposed bedrock acts much as the carpet in a sluice, only better! It is amazing just how much fine gold can accumulate there. These are prime areas for vacking.

Areas where people have been working with motorized sluicing equipment have also proven to be good. Even if they have worked the area down to the bedrock, they have been unable to clean the area as thoroughly as it can be cleaned with a Vack, and generally, the richest areas are right on the bedrock.

The greatest demonstration I have ever seen about how gold traps in bedrock and moss, and how much work it is to recover it using conventional methods, is contained in Dave McCracken’s video, “Modern Gold Mining Techniquies.”

Although I have not mentioned finding nuggets with this equipment, it certainly does find them! Even areas that have predominantly fine gold in the high bedrock will trap nuggets during flood storms, and if they are there, this equipment will help you get to them as nothing else will.

Since you do not work directly in the active waterway, and this equipment does not put anything into the waterway, there are no dredge permits required for the use of these units, at least in the state of California.

All in all, Vacking has such a wide range of applications, in so many areas of the country, by such a wide range of people, that the gain in popularity is very understandable. It can only be expected to grow.

If you should get the Vacking bug, be sure you look for us out there, because that’s where we will be every chance we get!

 

By Dave McCracken

How much you need to qualify a gold deposit in advance depends upon the additional investment that will be required to gear-up for production.

Dave Mack

In placer mining, there are fundamentally two kinds of sampling:

1) Discovery: Attempting to locate a higher-grade deposit of value inside of a larger volume of lower-grade material.

2) Quantification: Extracting and analyzing smaller portions, to gain a perception of how much value exists within a larger volume.

The general concept behind sampling is to minimize investment into a specific mining property, or a particular project, until there is enough proof that a mineral deposit exists which contains enough value to justify a more substantial investment.

The kind of sampling that you should do, and how much is necessary, largely depends upon the ultimate objectives, and/or how large of an investment you will make to implement a commercial project – especially that portion of the investment which cannot be recovered and re-committed to some other project at a later time.

For example, if you are going to join The New 49’ers Prospecting Organization to gain access to 60+ miles of mineral properties in northern California, and decide to devote an extended period of time into searching for and developing high-grade gold deposits along those properties, the money you would spend outfitting yourself with a sampling dredge is something you can depreciate over the extended period. This is because the investment will not be confined to a single mining project or property. When you are done, because the dredge and gear will be accessible, you can regain some of your investment by selling the used equipment.

How much sampling would be necessary in advance of making this investment? Not so much, because most of the investment is not committed to a single mining property. Before a final decision is made, perhaps it would be worth spending a week of your time participating in a Group Mining Project, to obtain some direct exposure to the activity, and see if this is how you want to spend your time.

On the other hand, if you were considering a substantial capital investment to start up a full-scale commercial dredging program on one specific mining property out in the middle of Borneo’s rain forest, where accessibility is only available by helicopter; it would be wise to first send in a sampling-team to confirm the existence of commercial deposits that will allow you to make a reasonable return on your investment. Knowing that most of the capitalization into this kind of mining project is unlikely to be diverted to some other program at a later time, how much sampling would be enough? It should be enough to:

1) Verify that commercial deposits exist on the property; and,

2) Quantify the deposit(s) well enough to become certain that the commercial value of the project is justified.

Sampling is a careful, organized method of attempting to locate high-grade mineral deposits; and then, obtain a reasonable perception of the value they contain.

Here are a few basic sampling principles:

1) The larger the sample, the more accurately the sample results will represent the larger volume of material that has not been analyzed.

2) The more samples you take, and the closer they are together, the more accurately the average result will represent the larger volume of material that has not been analyzed.

3) To achieve an accurate result in sampling, it is vital that you thoroughly clean all of the values from sampling equipment in-between samples.

4) As mineral deposits can be found at different strata’s within a streambed, a good sampling program does not only test in different geographic locations; but also at the different layers within a streambed. This is because it can often be more commercially-productive to mine a deposit only down to a specific strata.

 

On this river in Madagascar, the gold (plentiful) was so fine, the sample material had to be dredged into a large catch basin suspended between two boats, and then processed using specialized equipment on the bank.

5) To be effective, recovery-equipment used in sampling must have the capability of concentrating the values which exist within the deposit. Where special recovery equipment is needed, and the sampling must be accomplished with portable dredging equipment, it is sometimes necessary to dredge the samples into a floating catch-container. Then the samples can be carefully processed on land.

Sizing the gold being recovered, and the gold that is not being recovered, is an important part of a sampling process.


6) Care must be taken to ensure that foreign material is not introduced into the material being sampled which can render the result inaccurate. Just as this has to do with foreign material from other geographic locations, it also has to do with material from different strata’s within the streambed, if layers are being tested independently of each other.

7) The smaller the sample being analyzed, the more the result can be thrown off by the introduction of foreign material (called “contamination.”)

8) Tailings from a sampling recovery system should be carefully analyzed to see what values are being lost; and whether steps can be taken to recover the values in a production operation.

9) Ultimately, only the values that can be recovered during production should be included in the final business projections.

10) Care must be given to measure the amount of raw volume that is excavated to extract a sample. Because the value recovered must be related back to the amount of material that was moved and/or processed to obtain the result. This relation will need to be measured against the volumes and costs associated with a potential production operation.

For example: If an average cubic meter of streambed gravel to be processed will produce $10 in gold (gold at $425/ounce), at a gross production cost of $4 per cubic meter, when a production dredge is operating at 100 cubic meters per day, you can predict a net income of $600 for each dredge participating in the program.

Sampling is generally accomplished in two steps: The first step is to locate the existence of a mineral deposit. Usually, when we use the term “preliminary sampling program,” we are talking about a project where the existence of high-grade deposits still needs to be confirmed.

The second step is to sample the deposit(s) enough to gain a perception of its value. And that’s what this article is really about; how much quantification is necessary? The answer to this question largely depends upon the additional investment that will be required to gear-up for the desired volume of production.

Where we dredge along the Klamath River in northern California, using the very same equipment and support-structure in sampling as we do in production, we do not have to do very much quantification of a deposit before launching into production. This is because just finding the high-grade is reason-enough to mine it. Although, we usually do devote several samples in an effort to find a low-grade area where we can place tailings. Then, we establish the value of the deposit as we mine it.

The reason we can do this, is that under these circumstances, there is no substantial amount of increased financial risk when we transition from sampling into production.

Local miners were recovering rich deposits in the Cambodian jungle using very primitive, low-volume methods. Here was a good place to start with a sampling dredge.

However, many situations are different from this. Some mining projects are just in the start-up phase. Some mining prospects are in remote locations. Under many circumstances, to minimize risk, it is wise to begin with portable sampling equipment to complete the preliminary sampling phase of the program.

Local miners were supporting their villages in Madagascar by digging gravel from the bottom of the river out of boats using long-handled shovels. Our sampling later proved they were digging on the strongest line of gold in the river.

In this case, the question remains how much quantification is necessary to support the evolution to the next level of operations? This will always come back to the program objectives – which often have to remain flexible, depending upon what is discovered during sampling.

Here are several different levels of quantification:

1) Doing enough additional samples to prove that a high-grade deposit justifies bringing in a larger-sized suction dredge to go into production. As part of this, it is important to work out the best type of recovery system to use, and decide how many production-shifts you will run. Night operations require special lighting equipment.

2) Doing enough samples along a stretch of river to prove that high-grade deposits are extensive enough there to justify bringing in multiple production dredges, and setting up a substantial support infrastructure.

3) Doing a series of controlled samples, an equal distance apart, along a portion of a river, to statistically-quantify the value of a mineral deposit. This is often done under the watchful eye of a consulting geologist who will certify the results in preparation for a larger-scale mining operation with the use of mechanized machinery that might float on platforms.

  

 

4) Doing a series of controlled samples, an equal distance apart, for some distance across an entire section of river, to quantify the average-value of the river gravels. This almost certainly would be accomplished under the guidance of a consulting geologist(s) who will certify the results, in preparation of financial instruments for investment bankers or a public trading company.

 

By Dave McCracken

This system combines two classification screens to more-effectively separate material-feed into three separate size-fractions, each which is directed into a different recovery system.

Dave Mack


Riffles in box Three sections of screen

Classification is the Key to Fine Gold Recovery

It is well-established that if you want to effectively recover finer particles of gold, you must first separate them from the larger-sized materials which are being washed through your recovery system by a higher-velocity flow of water. The small-sized material can then be directed to a milder-flow of water over a shorter set of riffles. The smaller you can classify the size of the material, which can be directed by and even milder flow of water over lower-profile riffles, the finer-sized gold that you can effectively recover.

This is all rather easy to accomplish with surface processing plants where earth-moving equipment can be used to feed a plant some distance above the ground. Feeding a plant well above the ground allows plenty of drop for water and gravity to direct material through multiple sizes of classification screens. Then, gravity can be used to direct the different size-factions of material to separate recovery systems with controlled water-flows and riffle sizes specifically designed to recover gold effectively from each size-fraction.

Conventional Suction Dredges do not allow for Much Classification

I am not sure what the exact formula is, but I know from long experience that every inch you lift the feed of a suction dredge above the surface of the water, you lose a considerable amount of suction-power at the dredge nozzle. Therefore, since we have to accomplish both classification and gold recovery from a feed that can only be effectively lifted about 4-to-6 inches above the surface, our options are pretty limited.

Dredge manufacturers have worked out different ways to direct classified materials into slower-moving recovery systems. Generally these methods fall into three categories:

1) Placing a classification screen over top of a set of riffles. This way, smaller-sized material can fall through the screen into a slower-moving flow of water over riffles that are more-protected from higher-velocity water-flow. You see screened-over riffles in common use today.

2) Placing a classification screen towards the head of the sluice box, and then directing the classified material to one or two completely separate sluices which have a slower-moving flow of water over lower-profile riffles. This was most commonly seen in the form of side-by-side triple sluices during the 80’s and early 90’s. While effective, the problem with the side-by-side sluices is that the side sluice(s) normally have to be placed on top of the dredge’s pontoons. Therefore, in order for gravity to make everything work right, the initial feed to the dredge has to be lifted higher out of the water. This causes a power-loss at the nozzle. So you do not see as many side-by-side recovery systems in production on suction dredges these days.

3) Placing a classification screen somewhere towards the upper-end of the recovery system, and directing the classified material to a slower-moving recovery system which is located directly below the main box. This is commonly referred to as an “over-under recovery system, and remains in popular use today. An over-under system is most commonly accomplished in the same basic sluice box, which is constructed with a removable false bottom. By this, I mean two separate recovery systems, one sitting over top of the other, in the same sluice box.

I cannot go into which of these systems are better or worse; because there are too many variables in play, and experienced prospectors can work it out to get the best recovery possible out of any of these designs, each which would likely be comparable to the other. That’s because all three of these system concepts depend upon a single classification screen to remove some portion of the smaller-sized material from the higher-velocity water-flow which is required in a dredge.

This particular discussion has more to do with the effectiveness and size of material-classification. Remember, with conventional suction dredges, we are using water-flow to move all our material across any classification screen(s) that we are using. The larger the dredge, the faster and more powerful the water-flow must be to wash larger-sized rocks and a larger volume of material through the sluice. The faster the flow, the less time that smaller-sized material has to drop through a classification screen. The smaller the openings in the screen, the less opportunity smaller-sized material has to drop through the screen. The shorter the screen, the less opportunity smaller-sized material has to drop through the screen.

Each of these factors combine into to the effectiveness of the dredge’s classification. For example, the substantial flow of water to move 5-inch sized material over 10 inches of 1/8th inch punch plate does not present much opportunity for minus-1/8th material to drop through the screen. So while a separate slower-moving recovery system might be doing a better job recovering smaller-sized gold, perhaps the classification system is only allowing 5% of the finer-sized gold to be directed into the slower-moving recovery system. In other words, the effectiveness of your recovery system is largely affected by how you are attempting to classify and separate the smaller-sized material.

Therefore, on the subject of fine gold recovery with suction dredges, our first challenge is to try and accomplish effective classification as best we can out of a strong flow of water (strong enough to move the largest rocks you are sucking up through the recovery system).

Years ago, we overcame this whole challenge on commercial dredges by working out a mechanized shaker screen at water level which provided 100% classification of the dredge feed. Minus-sized material from the screen was dropped into a sump where it was redirected by a gravel pump to an elevated feed on a surface-type recovery system either on the shore, or on a separate floating platform.

But it is impractical and too expensive to try and place a mechanized classification screen on smaller-sized dredges — which also must remain more portable for sampling. Therefore, on conventional dredges, until someone comes up with something different (if ever), we must continue to make due with a water-flow to wash material across our classification screen(s). With this in mind, here are a few principles which I believe to be true:

1) The faster the flow, the more difficult it is to drop finer-sized material through the openings of a screen in your sluice box.

2) The smaller the holes in the screen, the less finer-sized material you can expect to drop through the openings out of the high-velocity flow required to move larger material through your sluice box. Example: Using the same flow of water and material, you could expect more fine-size material to drop through a 3/8-mesh screen, than a 1/8-mesh screen. This is because the larger openings provide a bigger doorway for material to drop through.

3) The shorter the length of a classification screen, the less fine-sized material you can expect to drop though. Therefore, we want the classification screens to be as long as we can get away with. Longer screen means more opportunity for finder-sized material to drop through.

4) Effective classification of finer-sized material can be accomplished better in stages. For example, first drop 3/8-minus material out of the fastest flow in the box. Then, using a slower flow of water, direct the minus-3/8 material over a 1/8-inch screen.

5) Since we only have 4 or 5 inches of drop to work with from the feed of a conventional suction dredge, there is only room for two levels of classification screen before we must drop the finest-sized material into a recovery system. Otherwise, we will be underwater where reduced gravity is not going to allow water-flow to work for us, anymore.

What to use for a fine-gold recovery system?

material in rifflesAs I have explained elsewhere, I believe it is necessary to direct finer-sized material over lower-profile riffles that will continue to remain fluid under a mild flow of water, even when they are full of concentrated (heavy) material. If you have not reviewed the theory on this, I strongly suggest you read “The Size of Riffles.”

There are different kinds of low-profile fine gold recovery systems on the market. Just take a look around and make your own choice.

We have been using the green, plastic Le Trap sluices to reduce the volume of our dredge and high-banking concentrates all the way back to the early 90’s. I cannot overstate how effective these Le Trap Sluices are. When set up with the proper water-flow, a Le Trap will recover all the visible gold from a feed of minus-1/8th material with losses that are so minimal as to be meaningless. We know this from panning the tailings hundreds of times over the many years.

So when we needed something to recover overwhelming amounts of fine gold using a dredge on a river in Cambodia, I started giving a lot of thought to how we could more-effectively classify dredged material down to minus-1/8th, and direct the material in a controlled flow over Le Trap-type riffles.

Dredge 1Dredge 2

Several very experienced dredge-builders and I created the prototype several years ago from a Precision 6-inch dredge. To accomplish our objective, we assembled two layers of classification screen, each which could be independently raised or lowered, so that we could adjust the water-flow over the riffles, and over each of the screens. The top screen is 3/8-inch mesh. This is to allow the larger-sized material and strong water-flow to wash through the box without affecting the plastic riffles along the bottom. Minus-3/8ths material drops through the top screen onto a 1/8th-inch mesh screen, where the water flow is substantially reduced. Slower water-flow then allows finer-sized material more-extended contact with the 1/8th-inch screen.Double screens over riffles

Material that drops through the 1/8-inch screen is then carried over the Le-Trap sluice by a mild flow of water. By adjusting the height of the lower screen over the plastic riffles, and the slope of the sluice box, we are able to control the amount of water-flow over the lower-profile riffles.

Since the sluice box in the 6-inch Precision was much wider than a normal Le Trap sluice, the prototype required quite a lot of work in a cut and paste project (using of 4 or 5 Le Traps) to create the first underlay recovery system for a dredge.

Fine goldWe invested quite a lot of time and energy into the prototype. All you have to do is look at how much (very fine) gold we found on that river in Cambodia to understand why we did it. We were shipping this 6-incher over to resume (sampling) where we had left off on that earlier project.

 

During trials on the Klamath, I was amazed at how much (very) fine gold we recovered out of just a minute or so of dredging loose material off the surface!

Our trial run on the Klamath River near Happy Camp in March several years ago turned up so much fine gold out of the lose surface gravel, that I hesitated over sending the 6-inch prototype to Cambodia!

I have been told for 30 years that there is so much fine gold in the river that we are losing out of our conventional dredges, if we could just recover it, we could make the river pay just by pumping any gravel! This new system seemed to prove that theory may be true, especially with these higher gold prices. But it was March and the Klamath was cold; so we shipped the original prototype dredge to Cambodia.Cambodia Dredging

I devoted plenty of time in Cambodia (underwater) observing three separate flows of material coming off the back-end of the recovery system; and it was poetry in motion!

I have a non-disclosure agreement with our clients in Cambodia, so I cannot go into details or images of how well the new system performed over there. But I can say that I devoted a lot of time underwater watching water and material exit the sluice box in three separate flows; and the double-screen system is by far the best thing I have seen on a conventional dredge for effectively classifying material into three separate size-fractions.

Because of that, my experienced buddies and I invested quite a lot of time during the 2009 mining season to adapt the double-screen system to my 8-inch dredge. 8-inch dredge

Building double classification screens, so they can be adjusted up and down to allow you to set three separate water-flows through the sluice box, requires quite a lot of labor! But getting this right is the foundation of this whole concept.

Here are some video links which demonstrate the system being used on my 8-incher. These give you a much better look at how we created a double-screen classification system over top of the fine gold recovery: Take a look at the size of the gold we were recovering!

 

As (bad) luck would have it, the State of California imposed a temporary ban on suction dredging just as we completed the double-screen refit on my 8-inch dredge. This forced us up onto the Rogue River in Southern Oregon, where we are limited to smaller-sized dredges. So my 8-incher had to be set aside.

Picking up on the idea of my double-sluice conversion over a plastic sluice, one industry-fabricator was recently promoting the idea of refitting conventional sluices (using the plastic sluice underlay) which do not include the double-screen classification, and do not allow the screens to be adjusted. I would advise caution on short-cutting these concepts. That is what prompted me to write this article. Since these conversions must be accomplished through custom shop work, I wanted to provide you with some background so you can make your own decisions.

While there is still a lot to learn, for the reasons I outlined above in points 1 through 5, I personally do not believe that you can classify raw material effectively from a 4, 5 or 6-inch (or larger) dredge being washed across an 8-mesh screen by high-velocity water.

I believe effective classification must be accomplished in stages; first to drop the 3/8-minus material out of the higher-velocity flow which is needed to push the larger-sized material through the sluice. Then, drop the 1/8-minus out of the much slower flow necessary to wash 3/8-inch material across the lower screen.

I believe you have to be able to adjust the height of each screen (set the water velocity) in order to get a workable water-flow over the riffles and over the 1/8-mesh screen. The water-flow cannot be so much that you boil-out the riffles, and it cannot be so little that you load the riffles. You also must not pack up the space between the two screens!

Eric Bosch and I first experimented with this double-screen concept in the early 90’s. But we made the mistake of fixing both screens (welded them where we estimated they ought to be). Our estimate of how much water-flow was needed between the screens was incorrect; the space between the screens packed solid with material; and the whole system failed.

Also, if you cannot adjust the water-flow over the riffles, and between the screens, you cannot compensate for different conditions in different areas.

Dave's goldAs an example, there is an overwhelming amount of heavy black sand and small iron rocks (and lead) along the Rogue River in Southern Oregon. We do not encounter this magnitude of heavies on our properties along the Klamath River in northern California. The heavies along the Rogue completely overwhelmed my fixed recovery system (buried the riffles on my 5-inch conventional dredge) at the beginning of last season. This prompted me to place smaller riffles below my (fixed) screen, spaced further apart. That worked better, and I recovered a lot of gold. But I believe I lost most of the (very) fine gold (I could see it in the last riffle) that was fed into my sluice box. This has prompted me to refit the recovery system on one of my 5-inch dredges for the upcoming season.

The images at the beginning of this article show an early version of the double-screen system that was designed for deposits we located in Cambodia. We did not find a single particle of gold on that river that was larger than the size of a pinhead. Since larger-sized gold was not present, we did not want to waste the (very) limited amount of room we had to work with by installing riffles for larger gold. Those images are helpful in showing the plastic sluice underlays (there are two of them, one following the other).

The images at the beginning of this article show the Cambodian version of the double-screen refit. Those images are helpful in showing the initial plastic sluice underlays that we were using (there are two of them, one following the other).

Header areaHeader with screen and miners moss

The images in this article also show a header section near the upper-end of the box. My initial theory was that the initial impact of the water and material must bottom-out on something other than plastic sluice underlays. We experimented with a combination of different kinds of heavy screens over top of miners moss or ribbed rubber matting to absorb the initial force of the water and material where it bottoms-out at the head of the sluice box. Fortunately, nearly everything we have tried in the header section seemed to work really well. As you will read below, we have since evolved completely away from using plastic sluice underlays… Header area after running

This is what the header area looked like under the screens when we shut the dredge off while dredging at production speed. You can see how classified material kind of mounds up there before flowing onto the slick plate of the riffle system. We are finding that quite a lot of (very) fine gold also gets trapped in the header section!

We have noticed that while in production, material tends to mound on top of the header section under the 8-mesh screen, and then wash off the mound onto the first sluice underlay. This is really good, as long as the mound does not rise up and pack-up the whole space between the screens.

While we were still using them, the plastic sluice underlays followed just behind the header section. This allowed water-flow and material to settle out and slow down before being washed across the lower profile riffles.

 

 

 

Two kinds of rifflesriffle section

Notice that the shorter section of riffles (remains protected by the top screen) are present only to process classified material which washes across the 8-mesh (lower) screen in the box.

Adding larger riffles for bigger gold

We have since evolved the system, adding two sets of different-sized riffles to catch larger-sized gold. We accomplished this by replacing one of the 1/8-mesh (lower) screens with a solid bottom that supports both sets of the added riffles. The false bottom continues to allow an under current to wash minus 1/8th material across a low-profile underlay, just like in the Cambodia version.

The first set of riffles on top of the false bottom is designed to process the material that drops through the 3/8-inch screen, but is too large to drop through the 1/8th-inch screen (1/8th-to-3/8th size-fraction). This would be for small nugget-sized gold. That size-range of gold is very easy to recover.

As I discussed in The Size of Riffles, the height of a riffle necessary to recover a piece of gold normally does not need to be much taller than the size of the gold you are trying to trap. So the first set of riffles for larger gold can be rather short. Notice that the first set of riffles continues to be protected by an extension of the top screen.

Then we added a final set of open riffles (not covered by a classification screen) to catch any gold we might suck up that is larger than 3/8th-inch (larger nuggets). For example, depending upon where you dredge, the Rogue River in Southern Oregon can produce a lot of gold in these larger sizes. But the river is loaded with fine gold, as well.

It is kind of hard to see in the images; but if you look close, you can see the plastic sluice under the false bottom where we placed the riffles for larger gold.

Since you cannot buy these double-screen systems ready-made, you either have to refit your own sluice, or arrange with a capable fabricator to do it for you. With this in mind, I will follow with some basic directions which we have learned from building several of these systems:

Building the System

If you look at a Le Trap, you will see that it has 3 important sections: There is a slick plate at the top. This is vital; because it allows the water-flow to smooth out before material encounters the riffles. Then there are some short riffles. These capture all the gold unless you over-feed the box with too much material at once, or unless you completely fill the short riffles with gold. Then there are some deeper riffles which more-aggressively capture all the rest of the gold when you do over-feed the short riffles up front. “Overfeeding” has more to do with the amount of heavy iron material, than light sand or gravel. I will talk more about this down below.

Close-up of rifflesThis image shows two sluice underlays following the header section (with no screens on top)

When we planned these sluice underlay riffle-panels, we included the slick plate up front, and then went about 50/50 the rest of the way using short and deep riffles. We did this because I wanted more of the short-type riffles that work so well in the Le Trap. But I did not want to eliminate the deeper riffles which create such a strong back-flow, especially at times when lots of material is being fed across the box. But through extensive trial and error using the third evolution of this system this past season, we discovered that the higher velocity flows that are necessary to move volume-amounts of classified material across the plastic riffles were also causing some of the trapped fine gold to boil out of the system. Too bad! We then tried Keene’s new ribbed rubber matting (good stuff!) and ended up with the same result (we were losing some gold). So it appears that these plastic and rubber riffle systems are better suited for final concentrating work, rather than being used in the volume production setting inside of a dredge recovery system (more on this below).

Because the double-screen assemblies are heavy, in order to manage them, you have to divide your sluice box into several smaller sections. How many sections depends upon how long your sluice box is. You will notice in the images at the top of this article that we divided my 5-inch dredge into three separate sections. One section is over the header area. The other two sections are over top of two identical sluice underlays. It is wise to divide the sluice underlay sections into exactly the same sizes. This way, the parts can be interchanged when it is time to reassemble your recovery system.

We build the double-screen assemblies so they rest exactly upon the sluice underlays. This allows us to take apart one only portion of the sluice box if that is all we want to look at or clean-up.

The screen assemblies are built so the aluminum side supports slide down inside the sluice box and sit directly on top of the side rails of the sluice underlays. This pins everything down snuggly against the bottom of the sluice box. Then we snap the screen assemblies down tight to make sure everything stays in place when we are running the dredge or moving it around on land or in the river.

Sluice Underlays

Close-up of matting
Close-up of both

Through a very substantial amount of trial and error this past season, we discovered that both the plastic sluice material and also the new Keene rubber matting were losing gold from under the twin screens.

Expanded metalWe finally found the right combination by using a wide, raised expanded metal over top of deep ribbed rubber matting. The aggressive expanded metal was dropping the gold out of the classified feed. Once it was in the ribbed mat, the gold was not getting away. This combination was so effective, we even replaced our header section with the same expanded metal, though we used miners moss underneath, rather than ribbed rubber matting.

We did multiple checks; and we were never able to find a single speck of gold in the final 25% of our recovery system, even though we were mostly dredging in fine gold pay-streaks (loaded with fines in the front section of the recovery system) all season.

This is important: The width of the sluice underlays (and screen assemblies) have to be a bit narrower than the inside of your sluice box. Otherwise, it is too difficult to get them in and out when you want to perform a clean-up or reassemble the recovery system. I always allow a margin of around 1/8th or 3/16ths of an inch, maybe even ¼-inch on a wider sluice.

Note: We have since replaced the sluice underlay in the drawing above by welding some 3/4-inch angle iron on both sides of the expanded metal to create side rails that the double-screen assemblies can rest on top of.

The following video sequence should give you a better idea of what we have ended up with as a sluice underlay:

The width of your side rails needs to be greater than the margin you are allowing between the sluice underlay and the side of your sluice box. This is so you will be sure that the sides of the screen assembly are going to slide down and meet the rails of the sluice underlay.

Double-screen Assemblies

Sliding the second screen into the frameThese add up to some weight; so you have to plan how to divide your sluice box into small-enough sections that you can lift the screen assemblies out of your sluice box without too much trouble. On the other hand, you want to minimize how many sections you have to make, because these are very labor-intensive to build.

The length and width of the screen assembly should match the sluice underlay, so that they will marry-up exactly when you set the screen assembly down on top of the underlay.

 

Screen LatchYou have to use aluminum plate for the sides to keep the overall weight of the screen assembly from adding up too much. The height of the sides needs to be at least as tall as your sluice box. I build mine high enough that I have room to adapt a latch to snap everything down tight.

Once you have the aluminum sides of your screen assembly cut to size, bring them all to your local machinist, and ask him to mill slots so that you will be able to raise and lower your two screens. If you bring the machinist one of the lag bolts you are going to use, he can mill the slots just wide enough to allow the lags to slide up and down freely, but not so wide that the lag is allowed to turn in the slot when you are tightening or loosening the nuts that hold the screens in place. Just to make sure I will have the full range of adjustment, I have the slots milled nearly the full height of the sides, to within about ¾ inch of the edge, equally at the top and the bottom. Each aluminum side needs three slots; one on each end and another in the exact middle.

You can source thin-headed lag bolts from fastener supply outlets. If you look, I’ll bet you can find them on line. If you cannot find them, then you have to grind the heads down on regular lag bolts, because normal heads are too thick and will take up too much space between the screens and the sluice box.

Helpful hint: The head-thickness of lag bolts on both sides of the screen assembly need to be included when you are deciding how wide your screen assembly and sluice underlay need to be for everything to slide in and out of your sluice box without too much difficulty.

Another helpful hint: If you cut the side plates all the same size, and have the machinist mill the slots exactly the same on all the plates, all the pieces will be interchangeable, and then you can jig-up to drill standardized holes in the side rails to your classification screens.

The lag bolts need to be heavy enough to support the weight of your screens (perhaps 5/16ths or 3/8ths). Different boxes have different widths, meaning heavier screens. It is better to go a little heavy on the lag bolts. The bolts need to be long enough to extend through the aluminum side, through the side rail of the screen, and have enough room for a flat washer and self-locking nut.

Screen frameStacking screens

Ideally, you build all your screens exactly the same size, so they can be interchanged. We accomplish this by rigging up a jig to cut all the side rails exactly the same; then to weld the frames all the same; and then to drill all the bolt holes the same. We drill the bolt holes in the side rails a little large to allow some margin for error.

Side rails for the screens need to be heavy enough to support the weight of your screens with you standing on top of them. By heavy, I am discussing rail thickness. Because, if you go too wide, you will limit how close you can adjust the distance between the screens. Thicker 1.25-inch-wide strap has worked well on my refits for the screen side rails.

Unless you want to buy whole new sheets of screen (expensive), I suggest you source used screen at your local metal scrap yard. The one we go to in White City, Oregon nearly always has a large supply in all mesh sizes. I gather that commercial screening plants replace their screens pretty often – most of it still in good enough condition to meet our needs.

The top screen (around 3/8th-inch openings) needs to be heavy enough to span the length and width of your screen assemblies without needing additional support, and without bending or sagging when you stand on top of the finished screen.

The lower screen (around 1/8th-inch openings) needs to be heavy enough to span the length and width of your screen assemblies without needing additional support.

Helpful note: I experimented with a finer-mesh lower screen (about 1/10th-inch openings), and had trouble with small particles of rock plugging up all the holes. We call this “blinding.” It’s when the holes in a screen all become plugged-up (or overwhelmed by too much feed), preventing the screen from doing its job. So it would appear that you do not want to use a mesh on the lower screen much smaller than 1/8th-inch.

Cutting screenWe have had good luck cutting the screens to size using a cutoff wheel on a hand-held grinder. If your side rails are made of thick material, you should be able to cut the screen to size and weld it down directly on top of the side rail frame. Grind all the edges nice and smooth, so your hands are not getting cut up once you start working with these screens on your dredge.

Helpful note: If you weld the bottom screen on top of the side rails, and the top screen on the bottom of the side rails, you will be able to loosen or tighten the center bolts in the side plate much more easily. I am talking about the lag bolts which attach the screens to the aluminum side plates. If you end up with your center bolts between the screens, it is much more difficult to get at them!

Another helpful note: You might want to drill your holes just off center through the side rails. This way, you can still get a socket on the nuts after the screen is welded on.

These helpful notes are things I have learned the hard way!

When you assemble the screens, a good starting point would be so that the bottom screen rests maybe just a little more than an inch above the plastic sluice.

Helpful hint: If you make the side rails on your sluice underlay too tall, it will limit how far down you can slide your lower screen.

We have had pretty good results lifting the upper screen about 1.25 inches above the lower screen.

This is important: To add more flexibility, if not already present, we modify the sluice box supports on the dredge so that we can raise and lower the slope of the box. This creates a very helpful mechanism for adjusting flow rates.

Once in the field, you can make adjustments to sluice slope and height of each screen to work out the needed velocity in three separate water-flows: First, the water-flow across the sluice; then the water-flow between the screens; and finally, the water flow across the top screen.

I already discussed above how to replace the lower screen with a false flat bottom which you can place riffles on top of to recover the larger classifications of gold. In my view, it is more effective to do this in the lower section of the sluice box (though, I mounted the riffles for larger gold in the upper-end of the sluice on my 8-inch dredge). I know this viewpoint is not popular with some prospectors, because they do not want to chance losing a bigger piece of gold that is allowed to get so close to the end of the recovery system. My answer to this is that gold is really heavy stuff! If there is some anomaly (like the gold is attached to quartz rock which makes the piece lighter) that would keep it from trapping in a set of riffles in the back-end of the box, it probably will not drop out in the front portion of the box, either.

Other than in a very rare occasion, the vast majority of the gold you will recover is small enough to drop through an 8-mesh screen. Some important part of that gold is so fine as to be difficult to recover using the recovery system on a conventional suction dredge. The journey of fine gold through 20 feet of suction hose, and then up through a diffuser (flare jet) places most of this fine gold right on the bottom of the material as it first flows into the sluice – right where you want it; right where it is most likely to drop through the classification screens out of the higher-velocity flows, which otherwise can wash it through your box like sand. Better, I think, to get the minus-1/8th gold into a safe holding area as the first priority.

If you look closely at the diagram just above, you will see another reason to put the larger riffles towards the rear-end of a double-screen system. See how all or most of the fines are directed through an undercurrent below the larger riffles? This means the larger riffles will not be getting flooded and loaded up with fine-sized material. So, while fine material gets more exposure to low-profile riffles (where it belongs), the deeper riffles remain more open so that larger gold has a place to drop out of the flow.

But that is just my view. You guys can do it any way you decide to!Riffles just after shut-down

The reason you see rocks on top of the double-screens, is because we turned the dredge off while we were pumping at production speed. See how the riffles are working? They are not loading up, and they are not boiling- out. This means the system was working!

I do my classification and sluice flow adjustments when running the dredge at normal operating speed while I am feeding the nozzle at production speed in hard-packed streambed. I arrange for a second person to kill the motor without notice. Then, when I disassemble the system, I can see how the sluice and screens are performing while I am pumping gold and gravel into them at production speed.

Between these explanations, the drawings above, the images and the video segments, you guys (or the fabricator who will help you) should be able to see how these systems come together, and how they work. They provide you with a whole lot more than I started with!

Here follows a video segment we put together at the end of this last season which demonstrates the most recent evolution of this very effective dredge recovery system:

Other Considerations

Trial runPossible need for added floatation: As I mentioned above, these double-screen assemblies are heavy. So if you do a refit of your sluice, you may also consider adding some floatation to your dredge. When I refit the original 6-inch Precision dredge for Cambodia (image above), I also had new, larger aluminum pontoons made up to provide enough floatation so that I could also stand on the dredge while it was running. Nice!

Having enough water-flow to make double-screens work: Every dredge is a bit different. Before refitting your dredge with a double-screen system, you might turn the dredge up and watch the water-flow across your existing recovery system and estimate if you will have enough water volume to provide sufficient velocity to meet the needs of three separate flows.

Overfeeding the system: Every recovery system has its volume-limits! Since I find nearly all of my high-grade gold associated with hard-pack, I design my recovery systems to process average material which makes up normal hard-packed streambed that was put in place during the evolution of a major storm event. Normal streambed consists of rocks which are fitted together, with smaller rocks and pebbles in-between, with gravel, sand and silt filling the smaller spaces. When taking apart normal hard-packed streambeds, the smaller-sized material only comprises a small fraction of the overall volume. Therefore, I have yet to overwhelm one of these double-screen systems while production-dredging in hard-packed material.

On the other hand, if you go out on the river and just start pumping sand or loose, classified gravel (like tailings), a much-higher percentage of the material will penetrate the screens and you will almost certainly overload (blind) the sluice with too much material – and perhaps even pack-up the space between the sluice and the bottom screen. Let me be clear: This double-screen system is not designed to process sand or loose gravel deposits or tailings from some earlier mining activity!

This same concern is true for any type of recovery system used on a suction dredge. So it is important for you to be mindful of the material that you are feeding into your suction nozzle. If it is a layer of sand or loose gravel, you should either slow down; or you can speed up and pump it through as fast as you can; and then go up and make sure your system is no longer packed-up before you start feeding pay-dirt into your dredge.

The fine gold needs to be present: The only good place to test the effectiveness of your recovery system is when you are feeding high-grade into your dredge. The more gold you feed into the recovery system, the better you can see how well it is working.

Effectiveness cannot be discounted just because you see a speck or two of gold down towards the end of your box. The thing to look at is where most of the gold is stopping.

So many times, I have watched others decide their recovery system is not working, only because they are not recovering much gold. You cannot recover much gold if it is not present in the streambed that you are dredging! So I suggest you reserve judgment until you test your system in high-grade.