By Jimmy Sierra

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

 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Good Hunting!

 
video subscription graphic
 

By Dave McCracken

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

Dave Mack

 

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

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

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

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

SETTING UP TO WORK AN AREA

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

DRY-WASHING PLANTS

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

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

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

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

“Non-motorized dry-washing unit”

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

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

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

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

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

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

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

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

SETTING UP A DRY-WASHER

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

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

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

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

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

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

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

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

DRY-WASHING AND CLAY-LIKE MATERIALS

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

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

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

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

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

DESERT PLACER GEOLOGY

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

 

By Linda Haze Gabris

 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

By Jude Colleen Kendrick

 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

 

 

By Dave McCracken

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

Dave Mack

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

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

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

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

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

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

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

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

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

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

 

“Shallow water dredging can be very rewarding”

 

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

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

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

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

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

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

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

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

 

BY MARCIE STUMPF/FOLEY

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

By Dave McCracken

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

Dave Mack

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

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

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

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

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

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

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

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

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

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

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

Here are a few basic sampling principles:

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

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

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

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

 

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

Here are several different levels of quantification:

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

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

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

  

 

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

 

By Dave McCracken

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

Dave Mack


Riffles in box Three sections of screen

Classification is the Key to Fine Gold Recovery

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

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

Conventional Suction Dredges do not allow for Much Classification

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

What to use for a fine-gold recovery system?

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

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

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

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

Dredge 1Dredge 2

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

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

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

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

 

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

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

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

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

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

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

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

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

 

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

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

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

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

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

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

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

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

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

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

Header areaHeader with screen and miners moss

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

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

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

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

 

 

 

Two kinds of rifflesriffle section

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

Adding larger riffles for bigger gold

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

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

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

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

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

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

Building the System

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

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

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

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

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

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

Sluice Underlays

Close-up of matting
Close-up of both

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

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

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

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

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

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

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

Double-screen Assemblies

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

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

 

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

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

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

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

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

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

Screen frameStacking screens

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Other Considerations

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

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

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

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

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

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

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

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

 

 
video subscription graphic
 

By Dave McCracken

There can be a lot of gold deposited under and around the boulders located within a pay-streak!

Dave Mack

 

It takes an incredible force of water to move boulders in a river. Once they are moving in a flood storm, they can deposit in low-velocity areas, just like gold does. But, since boulders do not have a higher specific gravity, mass for mass, than most of the other streambed materials, they can be washed downstream just about anywhere in the river during a major storm. So you should not only use the presence of boulders to guide you in sampling. You would be much better advised to focus your attention on the boulders that have been deposited along the common path of gold’s travel.

In shallow streambed material, you can sometimes detect where important bedrock changes are located by noting where the boulders have deposited within the waterway. For a boulder, or a group of boulders, to be found in a specific location along the river’s path, there may be a sudden bedrock drop-off, a large crevice, or some other kind of lower-velocity condition in that area which caused the boulder(s) to be deposited there. Everything in the waterway happens for a reason, even if you cannot always see what it is!

If the boulder(s) is located somewhere along the common gold path, that would be a prime spot to do some sampling. In this situation, I suggest that you do not limit your sampling to the area just behind (downstream) of the boulder, though. Go around to the upstream side of it, as well. Look for any bedrock change which may have caused the boulder to stop there. If gold has moved through that area, that same bedrock change could also have caused gold to concentrate there. Finding the bedrock change that stopped the boulder, and following the bedrock change across the waterway, is a great way to locate the common gold path.

You do not always find boulders with every rich pay-streak deposit. But, it is not uncommon to find many boulders keeping company with a good pay-streak. When you do find them, most of them will probably have to be moved out of your way as you work forward through the deposit.

MOVING BOULDERS BY HAND

There can be a lot of gold deposited under and around the boulders located within a pay-streak. To get most of the gold out from under a boulder and into your suction nozzle, usually the boulder has to be moved at least a little bit.

One of the most useful tools that can help a dredger move boulders is a 5-foot (or longer) steel pry bar. If a boulder is too large to be moved to the rear of the dredge hole by hand, it can sometimes be rotated around to one side so that you can dredge out from under part of it. Then, it can be rotated around the other way to access the remaining gold and material beneath. A long pry bar can be a big help to you in moving boulders around in this way.

The key concern while working around boulders is safety! Loose boulders in and around a dredge hole are the gold dredger’s greatest danger, especially when working alone. Boulders resting up in the streambed material are usually more dangerous than those resting on the bedrock. But, those on the bedrock can cause trouble, too, if they are loose and able to roll – particularly, if the bedrock has any slant to it.

As they are uncovered in a dredge hole, loose boulders should be moved and safely secured as a top priority. They should be placed at the rear of the hole, if possible. But, wherever they are placed, they should be positioned so they no longer pose any threat of rolling into the hole and on top of someone working there. You can place smaller rocks and cobbles under the boulders as necessary, to make certain they will not roll or slide.

If you start to uncover a boulder that is resting up in the streambed material, do not forget about it. Until it has been moved and secured safely, a loose boulder should be foremost in your mind. If it is not yet ready to be moved, and you still need to dredge around it to free it up some more, it can be useful to place an arm or a shoulder against the boulder. This way, you can feel if it starts to loosen up in the material. Do not place your arm, head, or shoulder near the underside of the boulder, however. Because, sometimes a boulder will loosen up and crash down very quickly, without much warning. Physical contact with the boulder is helpful when you cannot keep your eyes on it at every moment. The face mask limits your visual perception underwater – especially when you need to watch what is going up the suction nozzle.

The main concern here is to take all necessary precautions to keep yourself from becoming pinned or crushed beneath a boulder in your dredge hole. If a boulder pins any part of your body to the bottom, it may be difficult or impossible for you to get the necessary leverage to move the boulder enough to get out from under it. And, if you are working by yourself …? I know of two dredgers who ended their careers in just this way.

Also beware of fractured bedrock walls that tower over you. They can fall apart and drop in your dredge hole as you remove the streambed material that holds them in place. I got pinned once by a slab of bedrock that broke free of a wall as I dredged away the material that was holding it there. Luckily for me, it landed on my steel-tipped boot, and that I was dredging with another guy on that day!

The second greatest danger to a dredger usually comes from a cobble falling off the side of the dredge hole and hitting the dredger in some way — like on top of the head. This can finish off a dredger just as surely as a boulder. Or, it may cause some serious pain/injury. Fingers and other body parts can get smashed if you are not careful!

Most trouble with cobbles and boulders can be prevented simply by taking your hole apart with safety in mind. The proper method of taking a dredge hole apart has already been fully covered in my Gold Dredger’s Handbook, so I will not repeat it again here. But, as a point of emphasis, the fastest way to take apart a streambed also happens to be the safest way.

Production dredging goes very smoothly and quickly when you have some area of exposed (dredged) bedrock between the non-dredged material in front of you and the cobbles, boulders and tailings behind you. When you start uncovering a boulder in the material, you should immediately begin planning where you are going to move it, once it is ready.

If you run across an occasional boulder that you cannot move by hand, sometimes you can dredge the material (and gold) out from around and under it without having to move it out of the dredge hole. You accomplish this by moving other, smaller rocks out of the hole to make room for the boulder. In this way, if there are not too many boulders, you can keep moving forward on the pay-streak without the few boulders slowing you down very much.

But, if there are a lot of large boulders down along the bedrock, you will likely discover that at least some of them will need to be completely removed from your excavation if you expect to uncover very much bedrock with your suction nozzle. Some boulders will need to be removed to make room for other boulders as you move forward on the pay-streak. If you cannot remove the boulders from your dredge hole by hand, then you will need some mechanical assistance.

DIFFERENT TYPES OF WINCHES

COME-ALONG: A “come-along” is a portable, hand-operated winching device that can be of considerable help to a small-sized digging program. It can be used to move those boulders that are not huge, but which are too large to be moved by hand. Come-alongs range in size. I recommend a larger version of the better quality, rather than the really cheap, imported models. Come-alongs have a great accessibility factor, because you can carry one just about anywhere. Their operation is somewhat slow. But, they will give you that extra edge when you need to move just a few boulders, and you do not own or want to set up a power winch.

GRIP-PULLER: Several companies make a hand-winching device that rides along on a steel cable. There is a handle that you crank back and forth, similar to a come-along. Each time the handle is cranked in each direction, the device moves an inch or two along the cable. These units also come in different sizes. In my opinion, grip-pullers are a substantial step up from a come-along, both in pulling-power and dependability. I have used these units underwater, but find that the water resistance adds substantial work to the cranking action. Still, when you are working alone, having this device in the hole with you allows you to see what the boulder is doing while you are winching it

Where you can buy winching supplies

USING YOUR TRUCK AS A WINCH: If your vehicle can be driven to a nearby position, you can stretch a cable from the vehicle to the boulder. The proper direction of pull can be rigged up by running the cable through snatch blocks (heavy-duty pulleys) which can be anchored to trees, boulders or whatever is available. Then you can use the pulling-power of your truck to help move the boulders out of the way. Four-wheel drive vehicles work better for this, especially when they are carrying a load to increase tire traction. Suggestion: It is better to connect the cable to something on the vehicle’s frame, rather than just the bumper!

When conditions are right for it, using a vehicle to pull smaller boulders can be much faster than using a come-along. One person operates the vehicle, while a diver is in the water, slinging the boulders. Safety becomes a greater concern when more than one person is involved in the pulling and the slinging of rocks. Communication and coordination between the “puller” and the “slinger” are very important to prevent serious accidents. Suggestion: If you turn the truck around and pull in reverse, you can better-see signals from your partner, and sometimes you get better traction, especially on a 4-wheel drive vehicle. Another suggestion: It is better to keep your vehicle a respectable distance from any drop-offs (like into the waterway), just in case the boulder gets momentum in the wrong direction. I know of guy who got pulled over the side of an embankment by a boulder gone wild!

Larger-sized trucks, tractors, bulldozers, and other heavy equipment can sometimes be used to move bigger rocks with even better results.

AUXILIARY TRUCK WINCHES: Auxiliary automotive winches are also able to move small to mid-sized boulders for a dredging operation with excellent results. Some of those little winching units have a wondrous amount of power. A typical 8,000 or 10,000-pound electric winch will move a surprisingly-large boulder!

If you are going to be using an electric winch, you may want to consider installing dual batteries in your vehicle. It also helps to keep the engine running while you are winching, so the batteries can quickly regain their charge between pulls.

When using a truck-mounted auxiliary winch to pull boulders, it is a good idea to block all four wheels. This precaution helps to keep the vehicle from moving, rather than the rock you are trying to pull. The front tires should be blocked especially well. If there is an embankment to worry about, it is also a good idea to run a safety chain or cable from the vehicle to some additional anchor behind, like a tree or another truck. This will protect against losing your vehicle over the embankment if the boulder happens to roll the wrong way. Sometimes this added measure is necessary just to keep the vehicle from sliding during the pull.

Probably the best kind of auxiliary vehicle winch for dredging purposes is one that can be attached mechanically to the “power take-off unit” on your vehicle’s transfer case, if it has one. With this kind of winch, you can use the full power of your truck’s engine to pull rocks. Not only will this provide you with more pulling power, but you will not have to worry about your batteries running down.

There is also a lot of good to be said for the portable electric and hydraulic winches on today’s market. I know of many smaller-scale and commercial dredgers who use them. They are quite powerful! Portable electric winches can be framed up to (1) attach to a vehicle, (2) be taken out to the dredging site, or (3) even be floated on a platform, where there is deeper water. All that is needed is an automotive battery and a means of keeping it charged up. The portable hydraulic winches can be similarly effective. The winch controls can be extended out on a longer cable and even modified to work underwater, which can be very helpful!

LOG SKIDDERS: Most gold-dredging country is also logging country. So there are quite a few log skidders around that can be leased or hired to pull boulders for you. Log skidders are usually equipped with powerful winches. They can really do a job in pulling the larger boulders! Also, you can drive them into some pretty difficult areas. Hopefully, you can work out a deal that will be ideally suited to your operation; a deal perhaps, where you pay by the hour and have the skidder arrive at a certain time each day, or whenever you are in need of it’s services.

PORTABLE POWER WINCHES: Gasoline-powered, mechanical and hydraulic winches are available in all sizes. Generally, the larger they are, the more winching-power that they produce. But, the added size and weight also makes them more difficult to pack into some of the less accessible areas.

If you find a widespread, rich pay-streak with plenty of large boulders that need to be moved, you should set up on your dredging site the most powerful winch that you are able to haul in there. The more pulling-power you have available, the smoother and faster winching will go.

I never recommend that a dredger buy a portable power winch just because he or she will be dredging. It is probably better to wait until you know exactly what your needs are. I have worked many pay-streaks where no winching was needed at all. And, in many of the pay-streaks that did require winching, a number of the boulders were so large that the small, portable store-bought type of winch would not have been adequate for the job.

You can find some pretty heavy-duty used winches for sale at about the same cost as a lighter-weight, new portable unit. I advise waiting to see what you will need before putting your money into a winch.

Having said that, here is something to consider: Mechanical winches seldom have a control mechanism which can allow the operator to stand away from the machine where all the wrestling is going on (and in the line of fire if a cable breaks). While I have used some wonderful mechanical winches, there was never a time that we were pulling a big rock that I was not worried about something going wrong with all those tons of energy happening right next to me. There is a lot to be said about electric or hydraulic units that will allow you to step away from the danger with the controls in your hand.

WINCHING COBBLES IN DEEP MATERIAL OR SHALLOW WATER

As I have stressed in other articles about dredging, the main limiting factor to progress is in how quickly oversized material (rocks that are too large to be sucked up the nozzle) can be moved out of the ongoing excavation. In deeper streambed material, there can be so many cobbles that there is no longer any room directly behind the dredge hole to throw them. You can run into a similar problem in shallow water, where the cobbles must be lifted out of the water (where they become a lot heavier) to get them behind the dredge hole. In these types of situations, it is common to fill cargo nets with your cobbles and winch them out of your dredge hole in bulk. The following video sequence was taken in an operation where we were removing big lots of cobbles from a deep excavation in just this way:

SETTING UP A HOLE FOR WINCHING

Before you start winching boulders, it is a good idea to first make sure that you have located the lower (downstream) end of the pay-streak. You do not want to winch boulders onto any part of the pay-streak that you will be working at a later time. While the winter storms could possibly move some of the cobbles and dredge tailings which were placed on a pay-streak in error, it takes much more than a winter storm to move boulders from where you winch them. Believe me; it is much better to plan ahead, so you only need to move boulders one time!

BUILDING A RAMP

It takes a tremendous amount of winching-power to pull a boulder up and over another boulder from a dredge hole. The direction of pull is all wrong, and the second boulder will act like a barrier. The winching is much easier, smoother, and far less dangerous, if a ramp is built so the boulders will have an inclined runway to be pulled along. Cobbles can be used to make an effective boulder ramp. Therefore, an important part of setting up your dredge hole for winching is to construct a ramp/runway that can be used to easily remove the boulders, without them encountering difficult obstructions.

It can be really tough to pull a boulder out of a hole without a ramp.

Cobbles can be used to make an effective ramp for winching boulders out of a dredge hole.

One approach to setting up your hole is to dredge around a number of boulders as much as possible to free them up for winching. This way, more boulders can be pulled out of the hole once winching is begun. Then you can come back later to clean up the bedrock with your dredge.

To perform winching effectively, you will need plenty of air line attached to your hookah system. This is because it is necessary for the diver to sling each boulder and follow it to its final destination where he will disconnect it. Then, the sling and cable must be pulled back and attached to the next boulder. Since this process requires a lot of movement, depending upon the distance involved, you may need to attach an extension onto your air line to accomplish this smoothly.

FEASIBILITY OF MOVING BOULDERS

A dredging operation that requires a lot of boulders to be winched is going to move slower than if little or no winching is required. A winching operation almost always requires the involvement of at least one other person, sometimes even two or more. Those “extra hands” will usually expect to get something for their active participation in your dredging project. So you will find that when you need to use a winch, you will be moving slower through the pay-streak, and it will usually cost more to run the operation. Therefore, a pay-streak that has lots of boulders usually needs to pay pretty well to make the additional effort worthwhile.

The following video segment will give you a look at an organized winching program where multiple persons were involved:

Sometimes, you may discover an excellent pay-streak, but find that it lies beneath many boulders that have to be moved. Even though there may be plenty of gold under the boulders, after figuring the time and expense involved in winching, you may conclude that the gold recovery, though excellent, is still not sufficient to make the project economically feasible. Big boulders are not easy to move. Moving them takes time and money; more, sometimes, than the gold is worth. So, to avoid getting bogged down in an unworthy project, keep track of your daily expenses and your daily gold recovery. Then you will have some basis for calculating whether it is financially worthwhile to continue dredging in that specific location.

If your winching helpers are not full-timers on your dredging operation, and if the location is not too remote, you might arrange to have them arrive at a certain time each day to help pull boulders. That way, you can spend the morning setting up the hole to winch as many boulders as possible. Then, when your help arrives, the boulders can all be winched out of the hole at one time. After winching is completed for the day, you can let your winch helpers go, while you go back down and clean up the hole with your dredge. This way, you are not paying helpers to stand around with nothing to do while you are dredging. It can make a difference.

SETTING UP A WINCH FOR OPERATION

When you are using a portable power winch to move boulders in a dredging operation, the winch must be set up on a solid and stable foundation. It takes a tremendous amount of force to move a boulder. Sometimes, the boulder will move quickly. Or, sometimes, the sling will slip off the boulder, causing the cable to suddenly go slack. Maybe the boulder will loosen up and roll the wrong way, causing a sudden, heavy stress on the cable. When these things happen, and they do happen, you do not want your winch bouncing around or sliding off the platform. That could be extremely dangerous! The winch must be stable!

The winch also should be anchored to a solid object behind it which will hold its position much more securely than the boulders that are to be moved. A fair-sized tree, or a large boulder, directly behind the winch platform can work well for this purpose.

Also, the cable or chain being used to anchor the winch must be considerably stronger than the winch’s capability to pull. The last thing you need is your anchor chain or cable breaking while you are pulling a large boulder! This could cause the winch, and the winch operator, to be yanked off the platform, resulting in a serious accident. Undamaged, heavy-duty truck tow chains with the adjustable end-hooks are excellent for anchoring a winch. Make sure you get chains that are strong enough.

Your winch should also be anchored to a point which is lower than it is. If the winch is anchored from a low point, when boulders are being pulled, the winch will be held down more solidly onto the platform. If the winch is anchored to a higher point, during pulling the winch can be lifted off its platform. This can also be dangerous.

Sometimes, you will not be able to find a good location for your winch along the streambank. You prefer a location where the winch can be set up to directly face the boulders to be pulled, and which provides a level, solid foundation with a properly-located, fixed object from which to anchor the winch. But if that is not available, you can almost always find an acceptable foundation somewhere between two large objects along the bank. The platform may require a little concrete work to get it right. The winch can be anchored to one of the objects, while the other object can be used to attach a snatch block (heavy-duty pulley). The cable can then be run from the winch, through the snatch block, to the boulders that need to be moved. One advantage to this rigging setup is that if the cable does happen to break under a great strain, it will be less likely to fly directly at the winch and its operators.

Positioning the winch between two anchors on the bank,
because there is no easier way to get a straight pull with the winch.

When you set up a winch, it is usually best to position it so the boulders will be pulled as much as possible in the desired direction. The boulders will also need to be pulled far enough away from the dredge hole that they will not have to be moved again at a later time. Often, you will not be able to set up the winch in a position where you can directly pull the boulders in the desired direction. For example, you may want to pull them downriver, rather than toward the stream bank. This situation is most commonly corrected by using directional-change snatch blocks. A snatch block (pulley) can be anchored at a point from the exact direction that you want to pull boulders. The cable then runs from the winch, through the snatch block, to the boulder. In this way, you can usually move the boulders in any direction that you desire from a stable winching position along the bank.

Setting up the proper direction of pull by anchoring a snatch block directly downstream in the river.

Directional-change blocks for winching should be very heavy-duty. They need to be stronger than the cable being used, or the capability of the winch to pull. The best pulley is one that can be quick-released from the cable. This way, you do not have to feed all the cable through the block to get rigged for winching. Good winching pulleys are generally available at industrial equipment supply stores and at marine equipment shops. Directional-change blocks can be attached to trees or boulders with the use of additional cable, chokers or heavy-duty chain. You will find that a few extra tow chains (long ones) and chokers will come in very handy when setting up a winching operation. Chains which have the end-hooks on them are best, so you can adjust their length to meet your needs.

To minimize damage to the environment, you can place pieces of wood between the cable or chain and the trunk of any tree that you use as an anchor. When you anchor a directional-change block to a tree or boulder, you are almost always better off anchoring to a low point. This will reduce the chances of rolling the boulder over or pulling down a tree.

When you use a cable to anchor a winch or directional-change block to a boulder, set it up so that the pull will not cause the cable to become pinched (between two boulders or between a boulder and the bedrock) or be pulled into the material underneath the boulder. Otherwise, after the winching, you may have trouble retrieving your cable without having to move the anchoring boulder as well.

At times, you may need to set up a directional-change block, to pull boulders in a desired direction, but cannot find a downstream boulder that is large enough to use as an anchor. In this case, you can run an additional cable out from a fixed object further downstream on the opposite side of the waterway, and attach your directional-change block to the cable. Then, by increasing or decreasing the length of the cable, you can position the block right where you want it.

Setting up a directional-change block by extending it out on a cable from the other side of the waterway.

It is not a good idea to winch boulders with rope, even the smaller boulders being pulled by your truck or a come-along. When you use rope for winching, the rope stretches even if it is doubled-back multiple times for extra strength. And, it stretches. And, it stretches. Then, it breaks. Such breaks can be dangerous when working around boulders. Also, it can quickly exhaust your supply of rope. Rope is just not strong enough for the job. Steel cable is best. You might get a deal on good, used steel cable from the scrap metal yards. Call around to find out who has it when you need it. Scrap yards usually sell it at scrap prices, by the pound, even if it is in good condition.

The cable you use on your winch should always be considerably stronger than your winch’s pulling capacity. The last thing anyone wants to see is a bunch of out-of-control steel cable flying wildly back in his direction. Faulty or worn cable should be replaced immediately and never used thereafter for winching.

Winching boulders involves an incredible amount of force. So does hauling logs by cable. Similar cables are used in logging operations to pull trees to the loading area. I have heard stories of logging cables snapping, flying back, and cutting a man in two. You are dealing with a similar amount of force when winching the larger boulders in a dredging operation.

WINCHING SIGNALS

During a winching operation, it will be necessary to have a diver in the water to set the sling on the boulders. The diver will also need to remove the sling from each boulder after it has been moved, and then return the sling and cable back to the dredge hole for use in moving the next boulder. This process will continue until all the boulders for that stage of the dredging operation have been moved.

Unless the diver is slinging boulders and operating the winch (a very slow way to go, unless the controls to the winch are in the water with the diver), another person must operate the winch, truck or other device that will be doing the pulling. Once you have more than one person involved in the operation, communication becomes a critical part of the process.

If the winch is a smaller one, or if a truck is being used to pull boulders, and the pulling position is in sight of the target boulders, the job might be accomplished with only one winch operator. On the other hand, in a normal two-man operation, if the winch operator is unable to maintain constant eye contact on the area where the winching is taking place, perhaps a third person will be needed to help with the communication. Each situation will be different. Since this need for immediate and accurate communication is a safety matter which requires on-site judgment, you will have to decide how many people are needed to winch safely.

Sometimes a truck can be turned around to pull backwards, and the driver can directly see and simultaneously carry out the diver’s signals. The controls on an electric winch will often allow a second person to be positioned well enough to see what is happening where the rocks are being moved.

While a boulder is being moved, the diver can watch its progress and signal the winch operator to stop pulling and/or give slack on the line so the boulder sling can be adjusted, if necessary, to successfully complete the movement as planned. The main point is that the diver must be able to communicate to the winch operator quickly and without error. The greater the pulling-power and/or speed of the winch, the more important it is that these signals be accurately received and acted upon quickly. Imagine that you are using a powerful winch to pull a large rock with a heavy steel cable and solid anchoring objects. If your boulder gets jammed against something else in the dredge hole so that it will not move, and you continue pulling with great force, something is eventually going to give. And, it might not be the boulder! This uncertainty is what you want to avoid.

If you are using a winch that does not automatically feed the cable evenly onto the drum, the operator will sometimes need to manually guide the cable. Otherwise, on hard pulls, if the cable starts crossing itself and is allowed to pinch itself on the drum, it may become damaged and thereafter be dangerous for further winching. For this reason, the winch operator may need to focus some attention on the winch, rather than on the diver. In this type of situation, it is wise to include an additional person to help relay communication. Someone needs to be watching for the diver’s signals at all times.

Gasoline-powered winches make noise. So does a gasoline-powered hookah-air system supplying air to the diver. The diver also usually has a regulator in his mouth. With all of this noise present, and the diver having his mouth full, verbal signals are usually not very dependable – especially, if there is a substantial distance between the diver and the winch operator. For these reasons, I have often found visual signals to be more trustworthy, particularly when there is a person positioned at the winch to relay the diver’s signals to the winch operator.

In shallow water, hand signals can usually work pretty well. You really only need three of them: “PULL” , “STOP” and “GIVE SLACK ON THE CABLE”. I highly suggest you take a look at the standard set of signals that my partners and I use in our own dredging operation. These can be found in a special video segment included with an article I wrote about teamwork. Otherwise, create your own signals so that they can be quickly and clearly understood, and one signal cannot be confused with another. There is also a section on winching and signals in my video, Advanced Gold Dredging & Sampling Techniques.” You might want to check it out to get some ideas.

At times, you may be faced with the need to winch boulders out of a dredge hole located in deeper water. In this case, the diver will be heavily weighted down to stay on the river-bottom. He may also be some distance from the streambank. In this setting, it may be nearly impossible for the diver to surface to give timely signals to the winch operator. The process of getting up to the surface can simply take too long! When this is your situation, and if the water is not moving too fast, you may consider using a buoy, tied to a rope that is anchored near the dredge hole, to relay your signals. I personally have found the best and safest signals to be: (1) buoy underwater means, “PULL” (2) buoy floating at the surface means, “STOP PULLING” and (3) buoy bobbing up and down in the water means, “GIVE SLACK”.

This method of buoy-signals is relatively safe. If the buoy is anchored a short distance from the boulder, in order to pull the buoy underwater and hold it there, the diver would have to be away from the boulder on the “PULL” signal. If the buoy is floating, the diver can be anywhere, which is why it is the best choice for the “STOP” signal. You need to make certain, however, that nothing is allowed to snag the buoy’s rope (like the pull cable or an air line) which could pull the buoy underwater and cause a false “PULL” signal!

One other safety note:All divers must always watch their own hookah air lines during winching, to make sure an air line (or the signal rope to the buoy) is not snagged up in the cable or rolled over by the boulder as it is moved.

BOULDER SLINGS

When slinging boulders, try to make sure the pull cable will not rub too heavily or get crushed against other boulders. It is always best to protect the pull cable and let the boulder sling take the pounding. The boulder sling is going to be pounded anyway. Because of this rough duty, boulder slings should be replaced or repaired periodically.

One type of boulder sling often used out in the field is a long, heavy-duty tow chain with end-hooks which allow the chain to be quickly and easily adjusted to any length. This system gives you a fast set up. Just wrap the chain around the boulder in the proper place, connect the end-hook to give you the right fit, and she’s ready to go.

Tow chain boulder sling with end hook.

However, some boulders are smoother and rounder, which makes it more difficult to get a good “bite” with a sling made out of chain. Every time you start to pull, the boulder might move just a little and then the chain slips off. You can waste a lot of time working on a single boulder in this way; it can get quite frustrating.

Logging cable-chokers are also useful for making a cable sling that will tighten up on the boulder as you pull. This may improve the situation, but still not work problem-free on smooth, round rocks.

For round and smooth boulders, I have found the best remedy to be an auxiliary “boulder harness.” This homemade boulder harness consists of heavy cable, chain, steel pipe and cable clamps. It is very easy to construct. The sections of steel pipe slide onto the cable to protect it and to keep the cross-chains properly positioned. The harness is set up like a lasso. It pulls tighter around the boulder as stress increases on the line. And, it generally works well in pulling even the most difficult boulders.

How to put together an excellent boulder harness for winching.

PULLING BOULDERS

Some boulders come easy and some do not. A lot of the problem is in breaking the boulder’s initial suction/compaction in the streambed. If your winch does not have the power to pull a boulder the way you have slung it, sometimes you can break the boulder free by using a rolling hitch A “rolling hitch” is rigged by slinging the boulder backwards, then running the chain or cable over top of the boulder. This places the winch’s pulling-power along the most-leveraged position on the boulder. This will sometimes free a stubborn boulder by rolling it.

How to sling a rolling hitch.

When pulling boulders up and out of a dredge hole, you should pull them some distance away from the hole. Otherwise, if there are more boulders to be moved, they may begin backing up along your ramp and block the passage of any more boulders. This could require you to move them all again, which is a time-waster that you can avoid with proper planning in the first place. For example, take a look at the image at the beginning of this article. That is a top view of a winching operation we did on one of our Group Mining Projects a short while ago. See how we were pulling the boulders back well out of our ongoing excavation?

If you are dealing with relatively deep streambed material and a lot of boulders, you may want to set up an adjustable, directional-change block behind the hole. This way, the boulders can be winched out of the hole in several different directions. This will prevent them from backing up so quickly.

Setting up an adjustable directional-change block to pull boulders in several different directions.

Once the dredge hole has been opened enough, some of the boulders can be winched or rolled to the backside of the hole, rather than taking them up the ramp. Winching will start to go faster when you get to this stage. Depending upon the situation, it may be necessary to winch some of the boulders up the ramp and out of the hole to prevent too much jamming. Be sure to keep access to the ramp free and clear. Otherwise, you may get closed in with too many boulders in the rear of your hole. The more boulders that are jammed up, the more difficult it can be to clear them out of the hole.

Sometimes, when you have winched your boulder to its destination, it will end up on top and pin your sling underneath. If you are using a tow chain as your sling, you can usually just unhook it and have the winch pull it out from underneath the boulder. But, if you are using a sling made of cable, you may not be able to pull it out from under the rock without damaging the harness. For this reason, it is a good idea to have a second sling on hand to help move the boulder off the other harness when this happens.

DIVER’S SAFETY

A diver will be safest by staying well away from the area where a boulder is being winched, and the path it will be taking as it is being pulled. The forces involved in winching are more than enough to cause a very serious accident. Since the diver is underwater, the winch operator sometimes cannot see what is happening where the bolder is located.

What can happen down there, though, is when the diver sees the boulder getting hung up on things as it is being pulled along, he wants to move in and help it along with his pry bar. The less power that your winch provides, the more the diver will naturally feel the need to help the boulder along in this way. Never forget that your safety margin is considerably reduced when you get near a boulder while it is being pulled! A safer course of action would be to stop the pulling and reset the harness, or reset the direction of pull, or improve the boulder ramp, or find a stronger winch for the job. Or, you can increase the pulling power of your existing winch by double blocking…

DOUBLE BLOCKING

“Double blocking” is accomplished by attaching a snatch block to the boulder sling, running the pull cable through that block, and then back to the last directional-change anchor. This type of rigging will nearly double the amount of pulling force that can be exerted against the boulder by the winch and pull cable.

Double blocking back to the last directional-change anchor
will nearly double the winch’s pulling power against the boulder.

If even more power is needed, another block can be set up on the line to run the pull cable back to the boulder sling. The pulling force of any winching device can be increased by continuing to double block in this way. There is a disadvantage to all this rigging, however. It takes much more cable to pull boulders any significant distance. Also, it is equally more difficult for the diver to pull the boulder sling and cable back to the dredge hole after each boulder has been moved. With all that cable going back and forth, it can get pretty complicated – especially if you are dealing with a limited amount of visibility. Quick-release snatch blocks are a must when double blocking. This way, you can detach the pulleys from the cable without having to feed it all the way through.

Actually, one double block is not that hard to manage as long as you have enough cable. It is when you double block a second time that it starts getting difficult to keep track of which cable is going to where? But, this alternative is available to you if you need the extra pulling power to move a particularly large boulder.

Directional-change blocks, by themselves, do not give you an increase in pulling power. For a power increase, the cable must be doubled back so that the boulder is moved only half the distance that the winch is pulling on the cable.