BY ANTHONY “LITTLE TONY” STEURY, SR.

 

As usual, I awoke to the sound of a mother osprey’s loving shrieks giving instructions to her two young ones who had not yet mastered the art of flight. The sun was just coming over the top of Sugarloaf Mountain, quickly cutting the chill from the night air.

I could tell by the thundering sound of the rapids below my camp that the mighty Klamath River was rising at an alarming rate. The flood gates at the dam were being slowly raised, and I knew my time was limited. I felt that I must get down to bedrock under the rapids in order to find the gold that I knew had been waiting there for a gold dredger with modern equipment since the earth was formed millions of years ago.

As I quickly prepared a hot breakfast to help brace myself for the cold water I would have to endure, I reflected on the past two weeks dredging with my 6-inch dredge slowly moving yards of material, throwing cobbles, and moving small boulders to bore my way down to bedrock and get deep enough to escape the white water force that kept blowing me out of the hole. I was now at a point where most of the turbulence went over the top of my head, and I no longer had to work on my stomach with my face next to the nozzle intake to see. When I first started this hole, I was using 85 pounds of lead around my waist. One slight turn of the head would mean getting my mask or regulator ripped from my face by the turbulent force of the rapids.

I was snapped out of my interlude by the smell of burning bacon and a beautiful eagle gliding gracefully up the river taking full advantage of the thermal river canyon updrafts. Had I known then what events waited for me at the bottom of the river this day, I would have stayed in camp and dreamed of all the gold I had found in the years past.

As I put on my wet suit, my dog “Treasure” was already in the truck patiently waiting to go to our dredging operation as she had done so many times before. I think she knew our time was running out, and swimming the river to work our claim would soon be impossible.

I finished suiting up and grabbed all my gear. Twenty minutes later we were at the dredge, gassing up and getting ready to dive.

I took a quick look at my water marker, and it showed that the water had progressed 18 inches higher since yesterday. Not a good sign in the life of a fast-water dredger. Just as I started my engine and was preparing to slide down the suction hose into my hole, an ominous black cloud came from nowhere and totally blocked out the sun. It gave me a strange feeling as I looked up the side of the mountain and saw the old growth trees bending to a heavy wind by its awesome power. The cold, fast water slammed into my body.

As usual, my gallery was waiting for me in the bottom of the hole. Two ugly eels, three big suckers and many small fingerlings.

Without the sun, and because of a heavy flow of algae, it made visibility less then ten inches. I grabbed the nozzle and started plowing my way deeper around the base of a large boulder that I knew was lying on bedrock. Every day I had tried to move it with an 8-foot pry bar without success. “Today,” I vowed it would move. I threw caution to the wind and felt if I moved enough overburden from around its base, the force of the water would drop it on down behind me to the bottom tier of the rapids.

After steadily working for an hour and a half, I took a quick look at my watch and saw I had ten minutes of gas left. I was just about to go up and refill when the sun came from behind the clouds, allowing me to see that I had finally reached bedrock. There was a one-inch crevice starting at the base of the boulder making it a natural riffle. I took my small pry bar from my belt and pried into the crevice. Yes, I was right! Out came the gold into my suction nozzle. I had found the paystreak; I had outsmarted Mother Nature once again.

Just as I turned to go up and refill the gas tank on my dredge, I heard the familiar grinding sound of falling rock. A breathtaking pain shot up my leg causing me to spin around and grab my calf. As I did so, my mask and regulator were torn from my face. Experienced reflex made me grab my air hose to quickly retrieve my air source which I shoved back into my mouth, blowing out the water so I could breath God’s clean fresh air again.

At this point, after diving rivers and lakes clear back to when I was a young boy, I still panicked, causing me to hyperventilate. My mind started spinning to warn me I was about to black out. From out of nowhere, a voice was telling me to slow down my breathing, lie still and think things out before I became another one of the river’s many victims.

As my mind cleared, I started to run my hand down my leg, since without my mask, I could see only a few inches in front of my face. As I did so, again came the full force of pain which I was now more prepared for. After a quick search, my hand told me my ankle and foot were pinned under the large boulder that I had released with my foolish dredging around its base. I lay back again waiting for the pain to subside. Fighting panic, which would only bring me death, I took off one of my gloves and started to feel around behind me knowing my 8-foot steel bar lay somewhere near-hopefully close within my reach. It was the only chance of freeing myself, and a slim one at that. After groping around as far as I could reach, I was about to give up when my fingers touched steel. I arched my back and got three fingers around the point. Grabbing it the best I could, with my leg killing me, I pulled it toward me far enough to get a better grip and have total control. Just as I got it under and behind the boulder, I heard the engine stop from above.

I knew that there were only fifty-two seconds of air left in my holding tank. I twisted my body allowing me to put my unpinned leg against the boulder while, with arms above my head, I grabbed the top of the bar with both hands. I knew there would be only enough air for one chance to free myself. My mind raced back through my past. I thought of all the sporting events I had won in my youth. All the brave men who had died for their country telling me of all the things they still wished they could do. My family who still needs me and all of life’s battles I had won.

I felt a surge of power entering my body along with that gut feeling one always gets just before a win. I sucked in the last remaining air in my tank, pushing with my leg and pulling down on the bar with the 180 pounds of power that my body had to give.

Instantly, I fe1t the boulder move and I wrenched my leg free. Without hesitation, I ripped open my lead weight buckle release and shot out of the hole and down the rapids at breakneck speed.

In times past, this trip would mean a one-mile walk back up the river along a very rugged river bank, plus a one-hour delay swimming back across the river, floating down to my dredge, and retrieving all the gear I was forced to drop.

This day as my body was bounced along the bottom and slammed into boulders, I felt only the breath of joy while thanking a power greater than myself for this gift of life that was once again given to a mortal such as I. In a matter of minutes, my high-speed float trip was over, after being hurled into a slow water eddy which allowed me to drag myself up on a pile of cobblestones left by the old-time 49’ers.

As I laid back, totally exhausted from the pain and nerve-wracking experience, thinking about the fantastic gold deposit I had located, I looked up into the sky just in time to see my friend the eagle drop a wing tip to catch another updraft. He was, as always, looking after me and all of those who respect and love the river, saying farewell until another day dawned fresh in the life of the fast-water dredger.

 

By Dave McCracken

Specialized metal detectors will detect gold well-enough that they will sound-off on nuggets, deposits of smaller pieces of gold or even very small individual flakes of gold.

Dave Mack

 

 

Chrissy with her gold and metal detectorThere are many different kinds and models of electronic metal/mineral detectors to be found on today’s market. This is a guideline to give you the basic knowledge to help you choose the proper detector for your prospecting needs, and to help you use your metal detector as an effective prospecting tool.

There is a lot of electronic prospecting and gold nugget hunting activity going on at the present time. Consequently, there are different tools being used, along with several different popular approaches in how to properly-tune a detector and how to achieve the best results while searching.

It is important to point out that no two gold-bearing areas are exactly alike. An approach which might work better in one area, might not work very well in a different area. So, the purpose of this article is not to tell you what I think “the best” approach is. It is to give you information about each of the different approaches, so that you can gain a larger bag of tools to use when confronted with different situations out in the field.

I should begin by mentioning that the type of electronic detector used to find gold and other precious metals is not a “Geiger counter.” A Geiger counter is an entirely different electronic tool which is used to detect radioactive elements.

The type of electronic device used to prospect for gold is called a metal/mineral detector (“metal detector,” for short). Metal detectors are quite simple to use (once you understand them), and can be helpful in assisting you to locate gold or silver deposits or specimens once you have gained some personal experience in using one properly. While they are rather simple to use, it does take some practice with a metal detector before you can use one proficiently in gold prospecting activities.

There are many different models of metal detectors being offered on today’s market, most which are more useful to the treasure hunter than the gold prospector (two entirely different fields of detecting activity and procedure). Those detectors of most use to gold and silver prospectors generally fall under two separate categories: Beat Frequency Oscillator (“BFO”), and Very Low Frequency (“VLF”).

BEAT FREQUENCY OSCILLATOR

First we will take up the BFO, which is the simpler of the two—but is less-often found these days, due to the substantial electronic advancements of VLF detectors.

The BFO detector usually has two main settings, which are “metal” and “mineral.” As far as electronic detectors are concerned, the difference between the two is that “metals” are targets which are conductive of electricity–such as copper, gold, silver or iron. And, “minerals” are targets, or target areas, consisting of magnetic non-conductive materials such as magnetic black sands (Fe304). These are also known to prospectors as “black sand concentrates.” Electronic prospectors generally refer to them as “heavy ground mineralization.”

An iron object which has been in the earth for an extended period of time, and having thoroughly oxidized, will usually read-out on a metal detector as a mineral instead of a metal object–which it no longer is.

So the two basic settings on a BFO detector are “metal,” electrically conductive targets (gold and silver), and “mineral,” non-conductive magnetic particles (magnetic black sands).

The various models of detectors have different ways of sounding-out on reading targets. Some detectors have a light which turns on and off. Some have a meter with a needle on a dial–which will also give you an idea of the intensity of the signal given-off by various targets. Other detectors have a tone which changes in volume or pitch when passed over a reading target. Some newer-model detectors have an LED display which spells-out the different types of targets being encountered. Some detectors have a combination of these features.

Generally, the best type of metal detector for prospecting purposes is the type which includes an audio tone in which the audio pitch changes when the search coil is passed over a reading target, and which also allows a set of headphones to be connected. The advantage to using headphones while prospecting is that you can shut out the background noises from the surrounding environment and concentrate more intently on even the smallest audio changes which can and do occur while searching.

On most tone-changing BFO detectors, the tone will not only raise in pitch when the search coil is passed over a target for which it is set to sound, but it will also lower in pitch when the search coil is passed over a target of the opposite setting. For example, if a BFO detector is on the metal setting and is passed over a large gold nugget, the detector’s audio tone should rise in pitch. If the detector on the same metal setting is passed over top of a high concentration of magnetic black sand, the audio tone should lower in pitch. The same thing holds true in the opposite for the BFO detector which is adjusted to the mineral setting.

One other interesting thing to know about BFO detectors is they generally sound-out on the most dominant element, either “metal” or “mineral,” whichever is most present in the ground which the detector is being passed over. For example, if you are passing the search coil over ground which contains gold (this would read as a metal), yet there is a large amount of magnetic black sand in the same ground, it is likely that the BFO detector will read-out on the black sand as a mineral while ignoring the gold. Equal reading-amounts of both metal and mineral elements in a section of ground, in any quantity, will prevent the BFO detector from sounding-out on either element.

Because BFO detectors read-out so well on highly-mineralized ground, the presence of highly-mineralized ground tends to block-out reading traces of gold which lie in or under. This is known as “interference” in the electronic detecting field. Magnetite (magnetic black sands) has such a strong affect on metal detectors, that a concentration of only one percent magnetite in the ground may create a signal-imbalance which is hundreds of times stronger than the signal which might be given off by a small gold nugget.

So, a mineral reading on a BFO detector does not mean there is no gold present, only that there is heavily mineralized ground—which may be blocking-out gold readings.

One of the problems in electronic prospecting is that gold targets are often associated with highly-mineralized ground. Therefore, as a tool, the BFO has its advantages and limitations. In some prospecting situations, it can be very helpful to have a device which is good at pinpointing areas of concentrated heavy mineralization. The BFO does this exceptionally well.

This is further-discussed in my other article on this subject: Prospecting for Gold with a Metal Detector.

Some places where nuggets and larger flakes of gold become trapped do not allow heavy concentrations of black sand. One example of this would be a location (rapids) where the water runs fast over top of exposed bedrock during major flood storms. Such areas can be well out of the active waterway and directly accessible to metal detecting. BFO detectors can be very effective at helping to locate gold targets in places where heavy mineralization is absent.

GOLD TARGETS

Unfortunately, as a metal, gold is generally not picked-up very well by metal detectors. This is a comparative statement. Gold does not sound-off on a metal detector nearly as well as an iron object of the same size and shape. However, specialized metal detectors will detect gold well-enough that they will sound-off on nuggets, deposits of smaller pieces of gold or even very small individual flakes of gold.

No metal detectors are able to detect particles of gold dust at the time of this writing. This is probably a good thing, however; because there is so much fine gold spread throughout gold country that it would probably create additional interference problems on a sensitive gold detector.

Therefore, in electronic prospecting for gold, we are looking for flakes, nuggets and accumulations of gold. These are targets which will add up more quickly to something of good value.

It is important to understand that different makes and models of metal detectors are not equal in their ability to detect gold objects. Some detectors will just barely sound-out on gold objects. Others will not sound-out at all.

I highly recommend that any person who is buying a metal detector for gold prospecting purposes should bring along some samples of natural gold to test the various detectors before deciding which one to buy.

Small samples of natural gold and small nuggets are readily available by doing a search on the Internet or contacting a prospecting shop. This is to be sure that the metal detector you do buy will sing-out well when it is passed over natural gold objects, even very small gold targets. If a specific detector will not sound-out on gold held in the air, it will most-likely never detect gold targets located in the ground.

When testing-out the various detectors, it is better to use natural gold samples—like nuggets, flakes or a sample bottle filled with smaller-sized gold,. Some detectors will, and some will not, sound-off on small bottles that are filled with fine gold. Using natural gold targets is better than using a gold ring or some other type of jewelry. Jewelry is nearly always made of gold which has been alloyed with other metals (like copper)—which may read-out on a metal detector better than natural gold objects. Therefore, gold jewelry might give you a wrong idea about how well a metal detector will sound-out on natural gold targets.

The best detectors for finding gold are not necessarily the most expensive. Varying costs in detectors are sometimes in proportion to the amount of additional electronic circuitry that is built into the detector for extra features. These sometimes have little or nothing to do with the detector’s capability of locating gold targets.

Gold targets give a solid, mellow sound on a metal detector, similar to lead or brass. Pieces of steel wire and bigger nails usually give a stronger beep—or often a double beep.

The capability of a metal detector to sound-off on a natural gold target will partly depend upon what other metals the gold is alloyed with. Silver and copper make natural gold targets sound-out stronger. Nickel, mercury and platinum alloys make natural gold targets more difficult to find.

Metal detectors read-out on gold better as the pieces become larger. As an example, an average gold detector might sound-out very well when its search coil is passed over an eighth-ounce nugget from several inches away, yet not sound-out at all when passed over three times as much fine gold accumulated in a glass jar at the same depth or distance from the search coil.

Actually, it is not just the size of the target which counts. The object’s shape also makes a difference, and also the direction which a target is facing. A larger, more solid surface-area of gold will sound-out stronger. For example, a flake-shaped nugget is likely to sound-out better on a metal detector than a round nugget of the same weight, as long as the flat-surface area of the flake is facing in the direction of the metal detector’s search coil. Also, coarse and irregular-shaped nuggets, as commonly found in dry placer areas, residual and eluvial deposits, do not generally sound-out as well as nuggets which have been worked-over and pounded by flood storms in a streambed (because these are more dense and solid).

How tightly a gold deposit is concentrated also makes a difference in how well it will cause a metal detector to sound-out. Whereas a quarter-ounce of flake-gold inside of a jar might sound-out well on a particular detector, perhaps two ounces of the same flake-gold spread-out over a slightly larger area might not read-out at all with the same detector when the targets are at the same depth beneath the surface. This is one factor which is important for the gold prospector to realize: Any metal detector wills read-out on tighter concentrations of gold better than larger amounts of gold which are more widely dispersed. Metal detectors will also read-out on nuggets (larger solid pieces of gold) best of all.

DEPTH CAPABILITIES

How deep into the ground that a specific metal detector will sound-out on an object depends upon various conditions. Surprising to many, how much a detector costs may not have much to do with its depth-sounding capability. In fact, some of the less-expensive models are able to probe deeper, and pick up on gold better, than some of the more expensive detectors. The Federal Communication Commission has put a maximum limit on the signal-strength which can be used in metal detectors. So the idea that a more expensive model puts out a stronger signal to probe deeper is simply not correct.

The type of object has much to do with how deep into the ground that it can be located with a metal detector. Different kinds of objects have varying amounts of magnetic and electrically-conductive properties. Therefore, they affect metal detectors differently. Also, some detectors will sound-out on some kinds of objects better than others. As mentioned earlier, gold is not one of the better-reading metals, so cannot be picked-up with a metal detector as deeply as an iron object of similar size and shape.

Another factor which determines how deep an object will be picked-up by any detector is the size of the object itself. Whereas a 2-pennyweight nugget (1/10th ounce) might be picked up five inches deep into the ground with a certain metal detector, a 5-pennyweight nugget (1/4 ounce) might be picked-up eight inches deep into the same ground with the very same detector.

How much an object has deteriorated and has been absorbed into the soil is another factor in how deep the object will be picked-up. Iron objects tend to oxidize and become slowly absorbed into the surrounding material. This causes the target to appear larger and read-out more strongly, so it will be picked-up at greater depth with a metal detector. Once such a target has thoroughly deteriorated as an object, it will stop reading as a metal and start reading as highly-mineralized ground. Gold does not oxidize or deteriorate, so this factor does not apply to natural gold targets.

The size of a search coil on a metal detector is also a factor in how deeply the detector will locate objects. Larger coils generally are able to detect objects at greater depth than smaller coils. But they generally do not have as much sensitivity in detecting smaller gold targets. Smaller search coils have greater sensitivity to small objects, yet do not have the depth-probing capability that larger coils do. Medium-sized coils, from five to eight inches in diameter, often combine the features of having both a reasonable amount of sensitivity for the smaller objects, and acceptable depth-scanning ability.

One thing to keep in mind is that a larger coil will also increase the size of the area being covered by each sweep.

Many nugget hunters prefer to have a smaller search coil handy, because it produces the greatest small-object sensitivity (gold flakes), and because the smaller coils can get into tighter spots—like in and around tree roots and inside of exposed crevices in the bedrock, where nuggets are most likely to be found with a metal detector.

Almost all detectors today are made so that various-sized coils can be attached, depending upon what they are to be used for. When testing a detector, do not make the mistake of assuming that if the device sounds out well on a gold sample when using a coil of one size, it will also sound-out well when using a coil of a different size. Your best bet is to test the detector with the various-sized coils to see which work best for your particular needs.

One of the most important factors determining how deep a metal detector will sound-out on a gold object is how much mineralization (interference) is present in the ground that is being prospected. More minerals equal less depth. This is especially true of BFO detectors. Because black sands usually exist, and sometimes actually concentrate, within the very same streambeds or soils where gold deposits are located, metal detectors are not always used to directly detect gold in streambeds or material of substantial depth. They are sometimes used to scan places where there is a very shallow amount of gravel or material (if any) present over top of the gold (exposed bedrock).

One excellent use of the BFO detector as a prospecting tool is to locate concentrations of black sands in a streambed. Black sands often accumulate in the very same locations that gold does (pay-streaks). From your fundamental knowledge of placer geology, after potential pay-streak locations have been pinpointed, those specific areas can sometimes be scanned with a BFO detector to locate the increases in other heavy elements. Specific sites which sound-out heavily on the “mineral” setting can then be sampled by conventional gold mining techniques.

VERY LOW FREQUENCY DETECTORS (VLF)

The VLF detector is a more recent development in the field of electronic prospecting. Very Low Frequency detectors may come under other names or descriptive abbreviations such as VLF, GEB, MF, GCD and others. These are designed with circuitry which is able to cancel-out the effects which highly-mineralized ground has on a BFO detector. VLF detectors have the ability to look through or past highly-mineralized ground and detect metal objects (gold) that may not read at all on a BFO metal detector.

The VLF, being able to cancel-out interference caused by mineralized ground, is more suited for locating gold deposits and gold specimens directly. However, it still remains true that gold targets will have to be large enough, or located close enough to the surface, or deposits will have to be tightly concentrated enough, to sound-out on a VLF, just as with a BFO detector.

Just because a particular detector is of VLF design, does not mean it will sound-out well on gold. In fact, there are some VLF detectors which have difficulty in sounding-out on gold samples at all. So this type of detector must be just as thoroughly tested using natural gold targets before buying for prospecting purposes.

The VLF detector, being a mineralization-cancelling device, sometimes does not have the ability to detect the heavy black sand concentrations the way a BFO detector is able to. Consequently, a VLF is more often better-suited for scanning directly for gold, whereas a BFO is generally better-suited in helping the prospector locate gold deposits in an indirect sort of way, by finding the highly-mineralized ground within a gold-bearing area.

MULTI-PURPOSE DETECTORS & SPECIALIZED GOLD DETECTORS

VLF detectors are sometimes also constructed with discrimination circuits that are designed to cancel or identify specific types of targets—like bottle tops, aluminum foil and pop-tops. For the most part, this type of electronic circuitry is better-suited for treasure and coin hunters. When used in prospecting for gold targets, discrimination circuitry sometimes has a tendency to also reduce the detector’s depth-probing capability, especially in highly-mineralized soil or streambed material. Since gold targets are already difficult to locate, it can sometimes be better to not utilize additional circuitry which could hamper sensitivity towards gold.

However, some conditions do exist in which discrimination circuitry may assist a gold prospector. If using such a detector, always test it against a sample-nugget planted in or on the ground that you are probing, to determine whether or not you can trust the discrimination circuitry.

There is a lot to be said about having a small natural gold target along with you at all times when you are prospecting for gold with a metal detector. This way, each time you decide to try something new to try and get the most out of your detector under changing circumstances, you can confirm the results using a target which is similar to what you are hunting for. It is common for electronic prospectors to glue a test-nugget for this purpose to a poker chip, which can be tossed to the ground and easily spotted again.

Some of the newer, specialized VLF gold detectors are utilizing specific discrimination circuitry called “Iron Identifiers.” This does not necessarily reduce the total depth capability in the detection of gold targets. In other words, the circuitry will identify iron objects which are nearly certain to be iron. The downside to the use of such circuitry is that if an iron target is too deep or too small, it might still be identified as iron. Also, if the ground is highly-mineralized, the accuracy of iron-identifying circuitry is likely to be reduced.

The best gold detectors which use a meter or other display to identify different types of objects, do not route the discrimination function through the same circuitry that produces sound variations through the headphones. In this way, you can obtain optimum depth probing and object sensitivity to your ears, along with some added visual ability to pre-identify what is sounding-out on the detector. This is all about reducing the amount of trash targets that you must dig up while looking for gold.

Some experienced electronic prospectors utilize discrimination circuitry (turning it on and off accordingly) only after a target has been located. This way, depth and sensitivity is not forfeited during preliminary searching.

Other experienced prospectors insist that no discrimination circuitry is needed. Once you are familiar with the area you are searching, and know the specific audio tone changes of gold and/or trash targets, you will form your own judgment of which targets (sounds) to dig and which targets to leave alone. Different prospectors have different methods. Also, different locations often require different methods. Some experienced electronic prospectors simply dig every target (sound).

Some VLF detectors are made with circuits designed to analyze targets. This means they are able to tell you if the target is a nail, bottle top, a nickel, silver dime or a piece of gold. Such circuitry has only limited accuracy in electronic prospecting; because highly-mineralized ground tends to interfere with the signal and can give a false reading in the analyzer. Still, the added capability can be useful.

None of these circuits are a problem with multipurpose detectors, providing the special circuits can be shut off or bypassed—and/or providing the additional circuitry does not hamper the detector’s efficiency in locating gold and silver targets.

Some VLF detectors are designed with manual ground-balancing controls, and others are designed with automatic ground-balancing circuitry. Some prospectors prefer the manual controls. Others prefer automatic ground-balancing. There is nothing wrong with automatic ground-balancing circuitry in gold prospecting, as long as it is fast enough to keep up with the rapidly changing mineralized conditions of the different areas you intend to prospect—and as long as the additional circuitry does not hamper the detector’s ability to locate gold and silver targets.

Some VLF detectors have been specifically designed as gold prospecting tools. Since most specialized gold detectors operate at a higher transmitting frequency, have extensive ground-balancing capabilities, and have special circuitry to avoid sensitivity overload in highly-mineralized ground, they definitely do have some advantages in their ability to locate small gold targets over most multipurpose detectors—or gold targets which are deeper in the ground.

The high-performance of some of today’s specialized gold detectors even make pinhead-sized gold targets recoverable.

Which detector you choose to buy will depend upon what you plan to use the detector for. If you plan to only use it for prospecting purposes, a special gold machine is probably best for you. If you intend to search for coins, caches, artifacts and lost articles, as well as prospecting for gold and silver, perhaps a multipurpose detector is best—or two separate detectors. Only you can decide.

I would suggest you buy your detector from a dealer located in the general area where you plan to prospect for gold. The local dealer will know which detectors are performing best in that area. Local dealers will also introduce you to other prospectors, and perhaps a local prospecting and/or treasure hunting club or association.

Communication with local prospectors can be a very big help in determining which detectors are best for specific areas. You can also get tips from them on productive places to prospect with your detector.

No detector made is the best for all locations. Some machines work better than others in wet or dry conditions. Some work better in hot or cold climates. Some detectors are affected by alkali “salts” in the soil or gravel more than others. When any of these examples is the case, a smaller coil might manage adverse conditions better than a larger coil. Each area is different.

Another reason to purchase your detector from a local dealer is the help and support that you will receive. Success in the field comes from understanding the workings of your detector, and perhaps receiving inside information on good places to hunt. The money saved by buying from a discount mail-order house may not be worth the loss of support you would otherwise receive from a local dealer—especially when you are just beginning.

When buying a detector which you intend to use for prospecting purposes, keep in mind that probably the most important feature is the detector’s capability of cancelling the heavy ground mineralization found in most gold-bearing areas.

Practice makes perfect. You must start with good equipment. The rest will be up to you.

ELECTRONIC PROSPECTING DRILLS

The following is a set of drills put together to give the new (or old) owner of a metal detector some practice with his tool and to allow him (or her) to get a good grasp of what the detector’s gold-finding capabilities are:

DRILL No.1: Take a file or electric grinder to a piece of iron or steel (like a nail), and allow the fine pieces of metal to fall into a container. Pour some filings onto a piece of paper and pour some glue over the filings to hold them intact. Pour more filings on top of the glue and then pour on more glue. Continue this until the conglomerate is giving off a strong mineral reading on your detector. Make three different sheets of mineralization; one giving off a very mild mineral reading, one causing a medium signal, and one which gives off a strong signal.

If you are already an experienced gold prospector, and have some black sand concentrates lying around somewhere, use a magnet to collect some magnetic black sand and use these instead of iron filings. Sometimes, you can get prospecting supply outlets to send you a small package of black sand concentrates. You can also find bags of mineral concentrates (which usually include some gold) which various sellers on the Internet market as panning sands. These are better than using a machine to create iron filings, because they are the actual material that you will encounter in the field.

These different mineralized conglomerates will give you a good idea of how your detector will react to different degrees of mineralized ground.

DRILL No.2: Acquire at least a half-ounce of placer gold, preferably more, with a variety of fine, flake, and nuggets so a wide range of testing can be done.

Carefully place the gold in a pile on a clean sheet of paper in a location where there is no other metallic object reading on your detector. Scan the gold with your detector from varying distances to get an idea of your distance-capabilities when scanning a concentrated gold deposit.

Now spread the gold out over a slightly-wider space on the paper and scan again to check distance. Continue to spread the gold out wider and wider until it no longer reads on your detector—or until you are picking up on individual flakes of gold. This drill will give you a good idea of what sized pieces and accumulations of gold will sound-out at what distances. Try different coil sizes to see what their capabilities are.

Pay particular attention to the specific sound-readings that you get when scanning over gold targets. These drills should be done with headphones. With some practice, you will start to be able to tell the difference between gold and other metallic sounds by the difference in the strength, crispness and tone of the signal. Stronger-reading metals will give a sharper and louder change in tone, whereas gold tends to cause a softer and more indistinct signal–especially when located in smaller amounts or at a distance. Do the drill and see for yourself.

DRILL No.3: Using the flake-gold and nuggets in different accumulations, as done in drill No. 2, place the different sheets of mineralization over the top of the gold and note the responses on your metal detector. If you have a VLF, practice cancelling-out the mineralized sheets and test to see what size-accumulations of gold can be picked-up while doing so. Try more and more mineralization, combining the sheets together if necessary, to see how much mineralization your VLF detector will look through and still have sensitivity to gold targets.

Notice how even a larger piece of gold puts out only an inkling of a reading when covered by heavy mineralization and/or scanned from a distance. Recognizing these very light signals is usually the difference between success and failure in electronic prospecting!

If you are doing these drills with a BFO detector, try combining different amounts of mineralization with the various-sized accumulations of gold. Determine for yourself on your own detector how much mineralization it takes to block-out the different accumulations of natural gold.

I am certainly aware that sometimes it is difficult to come by a collection of gold flakes and nuggets if you don’t already have a collection of your own. However, the time spent in locating some natural targets to practice with, or in talking a friend into lending you his collection–or in talking him into doing these drills with you—will be worth many times as much time spent out in the field with your detector.

These drills will not teach you how to prospect for gold deposits. Only practice and experience out in the field will do that. But these drills will go a long way to familiarize you with your detector and give you certainty on the use of it. They will help you with the basics that you will need to learn to prospect for gold with a metal detector.

HELPFUL TIPS ON TUNING

Each model of detector has its own set of operating and tuning instructions which you should follow. And, I highly suggest you familiarize yourself with every aspect of the manufacturer’s instructions. In addition, here are a few pointers which have proven successful in the prospecting field:

Some manufacturers recommend that their volume-changing detectors be tuned to just below the hearing range. The purpose of this is so that the slightest reading will make a sound— which can be easily distinguished from the silence. But for prospecting purposes, it usually works better if you tune your detector so the audio signal is always within hearing-range. This will use up the batteries just a bit faster, but it is much better to be able to hear the signal at all times.

The audio threshold (“threshold”) of a tone-difference sounding detector should also be set just in the hearing range. When looking for natural gold targets, just the slightest change can mean the difference of finding or missing a gold target. Changes in volume and/or audio tone also are an indication of changes in ground mineralization and let you know when adjustments are needed to ground-balance again and again.

Sometimes the detector’s audio signal will drift off to a lower volume range due to temperature changes or loss of battery life. If the audio signal is tuned into the non-hearing zone and drifts into an even lower range, you might be scanning for several minutes without having the detector tuned properly. That would just be a waste of time.

Sometimes a warming coil will cause the threshold sound to drift upwards. A cooling coil might cause the threshold to drift downward. Hunting in and out of water environments, while scanning the banks of a stream, might cause threshold changes. You should make adjustments as necessary.

The main cause for a detector’s tuning to drift is loss of battery life. When this occurs, it is time to replace the batteries with a new set so you can get the best performance out of your detector—which is needed when hunting directly for gold.

It is always a good idea to bring along an extra set of batteries into the field when prospecting. Because when they quit, you are finished until new batteries are installed. Extra batteries should be kept cool and dry. Zip-lock baggies work well for this.

Prospecting for gold targets directly with a VLF detector should almost always be done in the “all-metal” mode.

Setting Sensitivity: It is important to stress that you do not want to set the sensitivity too high on your VLF detector while prospecting in a heavily-mineralized area. A high sensitivity setting while testing a nugget in the air will show improved perception—and therefore can give you a false impression of the detector’s scanning ability for gold targets in the ground. It is better to do your settings while scanning over your test-nugget on the ground that you will be searching over.

Turning the sensitivity up too high in mineralized ground is similar to using high-beam headlights in the fog. You get lots of flashback and irregular sounds and false targets. If your sensitivity is set too high, your detector will operate in an erratic manner. There will be many false signals which do not repeat themselves (“flashback”).

Consequently, less sensitivity can give you more depth-penetration in mineralized ground. There is actually a middle ground, depending upon ground mineralization, which will give you optimum sensitivity without too many “ground noises” which are confusing and prevent you from selecting the real targets. Try and run with the sensitivity as high as possible—until the steady tone of the threshold begins to give off an uneven, wobbly sound while you are scanning.

I usually do not recommend using the factory preset marks on your detector controls. Such settings are for average conditions. Prospecting for gold targets requires continuous adjustment to ground-balancing, and the threshold and sensitivity need to be set as accurately as possible to ever-changing conditions. You need to get the most possible out of your detector to avoid missing gold targets.

“Peak Performance” on a metal detector for nugget hunting purposes in most cases is: maximum volume on detector, threshold set in minimum audio hearing range, maximum sensitivity without receiving too much flashback, and ground-balance to the average ground being scanned. When you accomplish peak performance on your detector, the rest is up to you! By this, I mean you will have to interpret which signals should be dug up.

Ground-balancing: Setting the proper ground-balance on your detector, and keeping it properly adjusted while you search, is perhaps the most important factor in successful nugget hunting. I cannot overstate this point; because without proper ground-balance, you simply cannot find natural gold targets—unless you just get lucky. All of the skills we will talk about in this article, skills and methods which will make you good at finding gold targets, all depend upon your detector being properly ground-balanced.

Always set your ground-balance to the average soil or material which you are searching. You will find the majority of gold nuggets in average ground. If you ground-balance to specialized heavier-mineralized zones which are not the average matrix, you may forfeit some depth-probing capability or sensitivity to smaller or deeper gold targets.

Detectors which come with permanently-set, predetermined ground-balance are usually not especially good for electronic prospecting.

You should hear a low hum when your detector is turned on properly (threshold sound). As the detector is raised or lowered from the ground, the threshold hum should get louder or softer. This tells you what needs to be done to get a proper ground-balance. Handling the ground-balance knob or button on your detector is similar to handling the volume control of a radio. If the threshold hum is disappearing as you lower the coil to the ground, turn the knob up. If the hum gets louder as you lower the coil, turn the knob down. The basic idea is to adjust the ground-balance knob (or press the button) until rising and lowering the coil to the ground creates little or no change in the threshold hum.

Ground-balancing has to be redone on a regular basis while prospecting. The reason for this is because placer deposits do not contain uniform amounts of magnetic mineralization. Water-flows create low pressure zones and high pressure zones from one place to the next. These different zones accumulate different amounts of mineralization during flood storms. Often, you can see changes in mineralization just by noting changes in the color or surface of the ground you are scanning. Also, changing from gravel-like material to bedrock surfaces almost always changes the amount of ground mineralization. Get into the habit of re-ground-balancing about every 15 or 20 feet, or about every five minutes, or whenever the ground conditions change.

Your detector will tell you what is going on. If the threshold hum is getting louder, it usually means there is less mineralization in the ground you are now searching. If the hum goes softer, the mineralization is increasing. With a little bit of experience, you will gain your own perception of when it is time to re-ground-balance.

It is almost never a good idea to balance a detector over top of a piece of metal in the ground. Move around until you find a non-reading area to ground-balance.

When ground-balancing, move your coil all the way down to touch the ground if possible. I say “if possible,” because you occasionally run across areas with so much mineralization that you are not able to put the coil within a few inches of the ground! “Alkali salts” in damp soil can sometimes also create so much interference that the coil of your detector needs to be raised several inches above the ground to search for targets. Naturally, depth penetration is lost by doing this. But sometimes you have no other choice. Sometimes you can also get around this problem by making adjustments to your detector’s sensitivity. This will allow you to search with your coil closer to the ground; but the reduced sensitivity will likely eliminate some perception of smaller or deeper gold targets.

Sometimes, you can obtain better results by ground-balancing your detector a little on the positive side. A slight positive ground-balance increases the detector’s sensitivity to smaller gold targets when hunting in an area of lighter mineralization. This means that the threshold makes a slightly louder hum as the coil is lowered to the ground. When operating this way, be sure to keep the threshold in the audio hearing range. You don’t accomplish this by adjusting the threshold; reset the ground-balance as necessary to remain in the audio hearing range when lowering the coil to the ground. Just a slight positive ground-balance boost is all that is needed. Some experienced prospectors like to operate in a positive range all the time.

However, you may find instances when working around highly irregular ground, vegetation and/or rocks when a slight positive ground-balance creates a problem. Lifting the coil up and down and around with a positive ground-balance setting can create a similar situation as with too much sensitivity.

In highly-mineralized ground, when there are too many flashback signals which could be real targets, you can try ground-balancing your detector to a slightly negative setting with the coil on the ground. This may reduce your sensitivity to some of the smaller gold targets. But it is likely to settle-out your machine, and it might make it possible to locate targets which otherwise would not be accessible.

Always bring along your small sample natural gold target (about the size of a match head). This should be glued to a bright colored poker chip, or something similar, to keep it from being lost. Some prospectors go so far as to drill a hole and tie a string to the poker chip to avoid losing valuable time searching for lost poker chips! When in doubt about your tuning, toss down the sample gold target, cover it over with the ground in question, and see how your detector reacts. It might not be necessary to cover the test-nugget. Just placing it on top of the ground may be enough to test the tuning of your detector over that type of ground.

One thing which should be mentioned is that while you are searching around, your threshold hum is likely to change. The answer is usually not to reset the threshold; it is to adjust ground-balance and sensitivity as necessary to challenge the changes in ground mineralization. Your sample gold target will be the final test of whether or not your adjustments are working. If you don’t have a small natural gold nugget, you really should get one! Otherwise, a small piece of lead will create a similar target.

Other Tips on Tuning and Setting up a Metal Detector for Prospecting: When you are operating a metal detector, it is good practice to remove all rings, bracelets, watches and other jewelry from your hands and arms (ankles and toes). They can give a false read on the detector. This is especially true when you are testing a detector before buying, or when you are tuning your detector to sound-out properly on a special metal target while passing it over or under the search coil with your hand. Sometimes, belt buckles, canteens, knives and other digging tools or large metal objects carried on a belt can create false signals when using the more sensitive and specialized gold detectors. Even metallic eyelets on boots can cause problems when scanning too close to your feet. It doesn’t take much practice to figure out how to solve these problems.

Make sure to adjust the shaft-length on your detector to a comfortable position. Bending over too far will create uncomfortable back strain when hunting for extended periods.

Also, when the angle of the search coil on the shaft is changed to fit a new set of search conditions, the detector must always be re-tuned to correspond with the new relationship between the coil and the metal shaft.

Some prospectors prefer to mount the control box of their detector on their belt or hip. This lightens the arm-load during longer periods of prospecting activity.

It is also a good idea to wind the coil connection cable firmly to the shaft. This way, it is not flopping around, giving false signals or getting caught on objects and vegetation. Be careful not to pull the cable so tight as to break inner wires and create irregular operation of the detector.

OTHER IMPORTANT FACTORS TO CONSIDER WHEN BUYING

If you are looking over a metal detector you are interested in buying, test it to make sure that its tuning does not drift on its own. This test can be done by placing a good set of batteries into the device, turning it on, allowing it to warm up for a minute, tuning it in, and allowing it to sit and run for 5-to-10 minutes. If the audio tone drifts during this time, you ought to look around for a similar detector which has better electronic stability.

CAUTION: Wetness and dampness are not good for the control box of any type of electronic detector. Be careful to avoid getting yours wet when working around water. If you intend to use a detector out in the field on a damp or rainy day, you can cover the control box with a clear, loose-fitting plastic bag and secure it to the shaft of the detector. The bag should be loose enough so you can work the various control knobs without having to untie the bag and take it off to setup or re-tune the detector.

HEADPHONES

It is important in electronic prospecting to use quality headphones. This point cannot be over emphasized. Some detectors work just fine with the headphones which come from the factory.

There are different types of headphones. Some are heavy and cover the ears thoroughly. Some are light. What is best for you will depend largely upon the conditions where you are going to search. For example, the heavy type which thoroughly covers the ears might not be very practical in the hot, quiet desert environment. But they might work exceptionally well in a cooler environment—say along the bed of a creek where running water is making lots of background noise.

Areas which include the company of occasional rattlesnakes might require the use of lighter, less sound-proofed headphones!

The proper headphones for a specific hunting environment are another area where the local dealer or members of the local prospecting club can make valuable suggestions.

It is a common practice for prospectors to shorten the length of cable on detector headphones to about 3 1/2 feet. This helps prevent the cable from snagging on branches and other obstructions when working in brushy areas or climbing over uneven terrain.

Some detectors have volume controls and others do not. Volume on a detector while prospecting should normally be turned to maximum. Don’t confuse this with threshold hum, which should be set near minimum audio level. If maximum volume on the detector is uncomfortable to you, obtain a set of headphones which have volume control. Then, turn your detector’s volume all the way up and use the headphone controls to turn the volume down if you must.

Many electronic prospectors highly recommend “sensitivity enhancers”—like those made by DEPTHMASTER. These help enhance the soft target sounds from gold, while lessening the noisier signals caused by trash and iron targets.

OTHER HELPFUL EQUIPMENT

A plastic cup or tray is sometimes necessary to recover gold targets, even in dry terrain. A plastic gold pan is helpful to work down material where water is present. Sometimes a portable garden rake is helpful for moving smaller rocks and obstructions away from a productive hunting area. A small G.I. shovel is helpful in some hunting environments. A canteen filled with liquid; tweezers, needle-nose pliers for removing gold from bedrock traps; and a small pick for digging and scraping. Sometimes the ground can be very hard. This is especially true when finding gold on hard caliche layers in the desert. A wide belt with a carpenter’s loop (for holding hammers) comes in very handy for a small pick. This keeps it out of the way, but also makes it quickly accessible.

A lot of your gear can be left at your vehicle, or carried in a backpack which can be set down at the hunt site. It is usually better to not load yourself down too heavy while prospecting with a metal detector.

Many electronic prospectors are using empty 35mm film containers to contain recovered gold targets. These are unbreakable, and the large mouth makes it easy to get a piece of gold inside. Zip-lock baggies are also helpful.

A magnet can be a very big help while electronic prospecting. Sometimes you can recover a faint-reading iron target right out of the dirt with a pass of a magnet. Otherwise, you might find yourself losing valuable minutes picking through the material, looking for a small piece of gold. Animal feed stores commonly stock a special magnet used for cows (traps small iron particles, preventing them from entering and damaging intestines). These magnets are powerful, yet inexpensive. You can mount one on the end of your small digging-pick or tape it to the handle of a plastic or stainless steel garden trowel. This way, the magnet is handy when you need it. Some prospecting picks are available which already have a magnet attached; very convenient!

A serrated-edge on a garden trowel also is helpful when you find yourself digging around roots or brush. Some prospectors keep one edge of their trowel sharpened just for this reason.

When working bedrock areas, a small crevice tool can be a big help to open cracks and crevices which are sounding-out on your detector.

Some kind of pouch or pocket creates a location to dispose of small pieces of trash and iron which you dig up. You only want to dig it up once! It is much better to remove all small trash targets from the playing field. With the continuous improvement of electronic prospecting tools, you could find yourself going back over the same areas again at a later time!

Some prospectors are using fishing or photography vests—lots of pockets. These come lightweight or heavy, depending upon the environment where you plan to hunt.

 

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

 
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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 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 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.

 

 

BY PAUL BADALI

Since we’re still in the mainstream of the dredging season, I’ve decided to share a few tricks I’ve picked up in my experiences with dredging over the past few years. Hopefully they will help to make your dredging a little easier.

After several seasons of use, dredge hose becomes cracked and needs to be replaced. I have tried to repair the cracks and holes in my 5-inch yellow hose with silicone R.T.V. glue, that didn’t work; so I knew I would be replacing it. The only 5-inch hose I could find in the dry desert state of Utah was a very light duct hose called Spirolite, which is used to blow insulation into attics. The hose is so light and thin that I decided both the first and second time I went in to purchase some it could not hold up under dredging conditions. But the price was so good (about $3.90/foot for 5-inch) that I finally bought a 10 foot length just to see how it would hold up in the Klamath River. I liked it so well that when Tony Dilmore, who had originally recommended it to me, showed up in Happy Camp with some, I bought another 20 foot length from him.

Spirolite has definite advantages in some dredging applications. First of all, it is extremely flexible. It is ideal for creek dredging where the hose often must be wrapped around boulders. Secondly, it is extremely lightweight weighing only about half what the yellow hose weighs, so it’s easier to pack down the bank or into remote dredging sights. It does not show excessive wear as I had feared it might. When I first looked at this hose, I pinched my thumb nail and finger nail together on the thin clear material between the spiraled ribs and was able to pinch a hole in it. But I can’t see any holes in my 20 foot section of hose after half a season’s use in the Klamath River. So, it seems to hold up well. It does develop small holes where it is clamped to the nozzle and the jet, but these areas are at the end of the hose and can easily be cut off when they get bad. And at $4/foot, you can afford to take this into account and buy five feet more than you need. And as for beating out plug-ups, you don’t have to. This hose is so flexible that it rarely plugs-up. If a rock does turn sideways and plug, you simply deform the hose with your hands, and the plug frees with no hammering on the hose!

There is one application where a heavier, stiffer hose is preferred over the Spirolite, and that is in deep or fast water. Because the hose is so light and flexible, the water can grab it and keep pulling it out of your hole. When I used this hose in the gut of the “Glory Hole” on the Klamath in about 15 feet of water, I had to keep the dredge near the edge of the river, use 30 feet of hose, and anchor it to the bottom at two points on the way out into the gut. The nozzle still washed out each time I went up to knock a plug out. But for calmer more shallow water, it’s the hose I prefer to use.

You should be able to get it at most large hose supply stores in larger cities. If they don’t recognize the brand name Spirolite, ask for the lightweight clear spiral duct hose they use to blow insulation into attics with, and get prices at three or four hose supplies. You may get it even cheaper than I did!

Has your swivel nozzle stopped swiveling after two seasons of use? Mine had. Sand and small rocks work their way down into the joint, and rust accumulates in there over the winter. But if you have access to an arc welder, the repair job is simple. Just cut or grind off the weld beads that hold the swivel joint to the nozzle, and remove the swivel joint. Inside you will find two rubber O-rings or pieces of rubber cord cut to work as O-rings. Pull the whole assembly apart, and use a wire brush to buff rust and sand off of all the metal parts. Clean the rubber cord or O-rings in water.

You want to catch any sand that falls out, and pan it. I found one nice flake of gold inside my nozzle when I cleaned it. You may wish to use some type of non-oil lubricant in the swivel joint before you reassemble it, such as graphite or silicone. I haven’t done this yet, but I suspect graphite is the way to go.

To reassemble, simply match the old ground-off beads back up, and tack it in the same spots with an arc-welder. I would not gas weld these beads, as I suspect it would get the rubber O-rings too hot and damage them. When you are done, your nozzle should swivel as good as new. While you have the welder in hand, touch up any wear you see elsewhere on the nozzle.

This last winter, I got about 26 feet of 36-inch-wide miner’s moss free! You may be able to do the same. I noticed that miner’s moss was used on the floor as mats in every entrance at a local high school. I found the janitor and asked if he would keep me in mind, and give me any old pieces he might be throwing out in the future. He was curious as to why I would want old mats, and we got into an hour’s discussion about dredging for gold. At the end of our chat, he said, “You know, I think we have a few old pieces we’re throwing out in a store room right now.”

We went to look, and he helped me wheel out three six-foot pieces, and one eight-foot piece of miner’s moss. They needed some cleaning up, but hanging the carpets on the kid’s swing set and using the garden hose soon took care of that.

The moral of this story is ASK. If you want something, ask. If you think people will say no, nine times out of 10, then just ask 10 people, and you’ll get what you want. Everyone has seen miner’s moss being used for foot mats. The U.S. Postal Department uses it, supermarkets do, banks do, etc. They all have to throw out the old and replace it with new. So ask for the old mats, and chances are you will get some!

I would also like to give some advice on moving your small-size dredge around on a big river like the Klamath. If you are not a good swimmer, and you are scared to death to swim across; then listen to your intuition, and stay on the side you’re already on. Know your own limits, and don’t get yourself into trouble. But, if you’re an average swimmer, and just a little apprehensive, then here are some tips on getting yourself, the dredge, gas supplies, and concentrates back and forth across the river without a boat.

Number one, buy a good set of fins. Good fins fit over your wet suit booties and are fairly stiff. They are not so stiff that they feel like cedar shingles, nor so soft that you can touch the tip of the fin to the heel, but somewhere in between. With a good set of fins, you have about as much power in your legs as a 2-hp outboard motor, and you can really cruise across that river! Always wear your wet suit without weights when crossing, and take it easy. If you’re not used to pumping fins, you can quickly get a leg cramp from over exertion.

The current will pull you downstream as you swim. Pick a calm stretch of river to swim across, and start way up stream from where you want to end up. Don’t choose a calm spot immediately above bad rapids, because if you don’t make it, you will be going for a very bouncy ride. If you are crazy like I am, this can be lots of fun, but it can also freak out your wife who watches the ride from shore!

To swim across, just float on your back, point yourself towards the other shore, and pump your legs. Don’t try to head up- stream and fight the current! Just start way upstream from where you want to land on the other side, and take a relaxed ride. The fins do all the pushing, just let your arms dangle. With fins and a wet suit on, it’s easy as swimming in a lake.

To take my dredge across, I load everything onto it, and push on the tail-end of the sluice box while kicking with my fins. I do not like a rope tied from the dredge to the shore. I do not swim a rope across first, and let that rope pull the dredge in. I play outboard motor with my fins, and I propel the dredge to the other bank. I lie on my stomach if pushing, or on my back if pulling. I feel much more in control of the dredge this way. I do choose a very calm stretch of river to do this, and I give myself twice the distance upstream that I think it will take to get across. It’s easy this way for one guy to get a dredge across by himself, and it’s a breeze if you have a helper also wearing fins.

Supplies and concentrates are also easy to get across. If you use a large 30-gallon tub to dump your concentrates into, you already own a small boat. You can put your weight belts, winch, tools, towels, etc. into the tub, and pull it with you as you lie on your back and kick across. It will sink if you tip it, and an inflated inner tube around the tub adds safety and more buoyancy. You can pull people in dry clothing across in a small rubber raft as fast or faster than they can paddle. You can also very easily swim a motorized sluice (high-banker) across the river in a small raft or an inner tube. You can fit lots more cargo in a rubber raft if there is no one in the boat! Obviously, when you want to come back across the river, you have to walk upstream; because you will be washed downstream as you swim back across.

There really isn’t much to fear from a big river if you are careful. You float like a cork in a wet suit. Don’t fight the current! The current is stronger than you are, so “go with the flow,” and let it work for you. Get good fins, so you have some push, and have a good time with it. In most cases, there has been less prospecting and mining done on the other side, so you may reap great rewards for your investment in a pair of good fins!

Good luck, and see you out there!

 

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!

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