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.

 

 
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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.

 

 

By Dave McCracken

As far as I’m concerned, if you are going to spend a lot of time dredging in cold water, a hot water system is definitely the way to go!

Dave Mack

Cold Water 1
“Photo by Tim Cook”

Can you recall ever standing alongside an unheated swimming pool or just next to the water’s edge on the beach, trying intently to muster the nerve to jump into the cold water? Perhaps you even tried to build up to the big leap by counting, “One, two, three.. .jump!” — only to find yourself still standing at the edge of the water after the countdown and feeling like your body is not quite under your control. This can often be the case when you are dredging in cold water. The key to successful cold water dredging is having the proper equipment — particularly those items needed to keep your body from getting too cold and uncomfortable.

Wetsuits

Wet-suits are designed to allow water to get inside the suit. Your body-heat then warms the water up, insulating you from the colder water that remains outside the suit. In really cold water, the main problem with a wet-suit is that initial frigid shock which shocks your body as the initial cold water rushes into your suit when you first enter the water. This happens again every time you re-enter the water after knocking out a plug-up in the jet tube or every time you take a break. This “cold water shock” has an accumulative affect on the body; and even the toughest people often find ourselves going “one, two, three” on the bank and have trouble making our bodies jump back into the water.

Some wet-suit divers lessen the pain of cold water shock by having a hot tub of water on the bank. They pour the hot water into their suits just before re-entering the water to help bring up their body temperature. Hot water systems that provide a steady flow of warm water into a wet-suit are even better — but we will address that topic below.

There are different types of wet-suits, some which are designed especially for cold water use. Cold water wet-suits are usually made of thicker rubber, have few or no zippers, and almost always have the hood directly attached to the wet-suit top. There is also the “shortie,” which is like a pullover wet-suit sleeveless T-shirt with or without a hood attached. A shortie can be worn underneath or over top of a regular wet-suit to create added warmth. In addition to the added thickness of rubber around your upper torso, a hooded-shortie prevents a lot of the cold water shock from running down your neck and back!

Important note: The more rubber you add for insulation from cold water, the more lead you must add to your weight belt(s) so you can remain firmly anchored to the bottom of the waterway when you are dredging. Also: The more rubber that is added around your upper body, arms and shoulders, the more constrained your arms and shoulders will be. Dredge work underwater is mostly stomach, arms and shoulder-work (movement). Therefore, adding more rubber increases the amount of effort required to get the work done. Effort in dredging is like money in your wallet. You only have so much. So it must be managed as efficiently as possible. Because, once you have used it up, your day is over.

Dry-suits

For cold water dredging or diving, dry-suits are definitely a step above wet-suits (when there is not a hot-water system). A dry-suit is designed to keep all of the cold water out. Basically, there are two different types of dry-suits available on the market: Those that use the rubber or nylon shell as insulation, and those that require additional insulation to be worn inside the suit. Both types work well; it is a matter of individual preference as to which kind is best for you.

Dredging activity is very hard on any type of suit. There are many different models and makes of dry-suits available. Some are designed more for sport diving rather than dredging and hard work. Dry-suits generally are quite a bit more expensive than wet-suits. However, you cannot rightfully put a price on comfort and warmth when you are spending many hours underwater working for a living. If you are cold and uncomfortable, you will not get in as much dredging time; and you will not make as much gold (money). So, my advice is to spend the extra money on getting a quality dry-suit if you are going to buy one.

Dry-suits generally require more maintenance than wet-suits. Mainly, the seals at the extremities and the zipper must be properly maintained. Most dry-suits have zippers which should be coated with bees wax every several uses and sprayed with silicone each time the suit is used. The seals should be sprayed just before each use. This allows them to slip on more easily, and prevents unnecessary stretching. The zipper is the heart of a dry-suit and must be handled with care. You have to be careful not to get sand in it, and not to sit on it or rub it heavily while moving rocks around in the dredge hole. I always glue a rubber flap over my dry-suit zippers to further-protect them from dredging wear and tear. Most manufacturers stress having a second person zip it closed rather than doing it yourself. This is because it is difficult to pull the zipper straight when it is behind you, as many dry-suit zippers are. If you damage the zipper, the suit is no good until you get the zipper replaced.

You will find that even the smallest puncture holes in a dry-suit need to be patched when diving or dredging in extremely cold water. Otherwise, you are constantly uncomfortable with cold water entering the suit from that location.

Hot Water Systems

Cold Water 2As far as I’m concerned, if you are going to dredge long hours in cold water, a hot water system is definitely the way to go! Water is usually heated with a heat-exchanging device mounted to the cooling or exhaust system of the dredge motor. The dredge pump is tapped to provide a water supply, which runs through the heat-exchanger, then through a steam trap/mixing tank, and then down through a hose to pour a constant volume of warm water into the dredger’s wet-suit. Some dredgers are using propane continuous-demand hot water heaters, but most use heat exchangers mounted to their engine exhaust systems.

Hot water heat-exchangers are available on the market. They are also reasonably easy to build. Most homemade exchangers are built with a long length of copper tubing which is either wrapped around the existing exhaust system or is coiled inside a separate housing through which the engine’s exhaust is channeled.

Photo By Tim Cook

The key to a hot water system is to provide an abundance of hot water. If you do not have plenty of hot water for all of the divers working on a system, then you will most likely end up pumping cooler water into each diver’s suit, which can be worse than having a wetsuit with no hot water system.

Hint: You can never have too much hot water — because you do not necessarily have to use it all.

Most ordinary wet-suits are adequate as hot water suits — particularly with the addition of a hooded shortie vest. Dry-suits normally do not make good hot water suits, unless they are modified. This is because the seals prevent the hot water from exiting the suit. After a while, all the excess water inside the suit cools down and makes the diver cold. Removal of the seals on a dry-suit would probably make it a good hot water system (as long as it is a tight-fitting dry-suit) — but this seems a waste of money when a far less expensive wet-suit will accomplish the same purpose.

The main problem dredgers can have with a hot water system is being scalded by extreme hot water or steam. This problem can largely be solved by adding a steam trap to the system. Some prefer to call this a “mixing tank.” A mixing container can be made out of PVC plastic tubing. One of the primary purposes of the mixing container is to be a holding tank for water and steam. So, if extreme hot water or steam is created in the system, it will have a chance to mix with the warm water in the tank before being pumped down to the diver. The mixing container should be mounted vertically on your dredge with the input coming from the top, and the output to the diver being on the bottom of the container. This way, steam is prevented from being pumped directly to the diver(s). Some systems contain a low-pressure relief valve at the top of the container to allow air and steam to release.

mixing containerThe mixing container must be large enough to absorb a shot of extremely hot water, but not so large that it allows the water to cool down before it is pumped to the diver. The mixing container allows the diver to feel the rise in water temperature much more slowly, so that the hot water hose can be removed from the wetsuit before it gets uncomfortably hot. Sometimes, the water can be so hot coming out of a heat exchanger, that a special steam hose must be used. In fact, just for safety, I always use heat hose on the connection from the heat exchanger to the mixing tank.

If the water coming out of the heat exchanger is too hot to pump directly to a diver — which is often the case — a source of cold water can also be tapped from the pump and directed into the mixing tank through a valve. By regulating the amount of cold water, you can adjust the temperature of the water being pumped down to the diver. This also increases the volume of warm water available to all of the divers.

Warm water is usually pumped down to the diver through the same kind of hose being used for air line. The hot water line and air line are usually taped together to prevent tangling and additional underwater confusion. The hot water line can be slipped into your wet-suit down through the neck. I usually poke a hole in my wet-suit near my chest where it is easy to slip the hot water line in and out of my suit.

Or, in extremely cold water, you can devise a splitter system which will direct some of the warm water to your chest, hood, each bootie, and each glove. This is the best way to do it if you are dredging in ice cold water. However, sometimes the splitter system can be avoided simply by having a hot water system which provides so much volume, that the warm water is forced out into these same extremities.

When dredging in ice cold water, if you do not have warm water directed to your hands, it is usually necessary to use three-finger wet-suit mittens. Otherwise, your hands can go numb from the cold. Three finger mittens are bulky; they prevent you from picking up larger cobbles with one hand, and they generally slow you down. With a good source of hot water to the hands, you can often get by with a good set of slightly-insulated rubber work gloves with the openings loosely rubber-banded around your wrists to prevent cold water from entering.

Dredge with snow on the decksAuthor was developing some of the early hot-water heaters on his first dredge in 1981 while working in the frigid waters of the Trinity River in Northern California.

It is necessary to warm up your dredge engine to normal operating speed for at least several minutes to properly set the temperature of the water directed to the divers from the mixing container. Once you get the temperature working right for you, you normally do not need to make any further adjustments on subsequent dives, as long as you are running the motor at the same RPM.

If you stand around for a few minutes with hot water pouring into your suit, there is usually no shock at all when entering the cold water. As a matter of fact, it can be a pleasure to enter the cold water after you run your body temperature up to the uncomfortable stage when you begin sweating.

A hot water system should be removed from the dredge when not being used, like during the warm summer months. Otherwise, the heat and vibration will tend to wear the heat-exchanger out unnecessarily. Also, even when not in use, if a hot water system is attached, water should be allowed to flow through it any time the engine is running. This will prevent unnecessary overheating of the heat-exchanger.cold water 3

Photo by Tim Cook

If you are tapping your dredge pump for a supply of water, be sure the water output is either closed off or underwater when priming your pump. Otherwise, there may be an air leak which can prevent priming.

The nice thing about a hot water system is that it will supply a continuous feed of hot water into your suit. This way, your body’s energy reserves are not being constantly used up to keep warm. As a result, you can be comfortable and get in more dredging time.

Important note: You can also be so warm that your body doesn’t want to work — like being in a hot shower. The solution to this lies in the amount of cold water you valve into the mixing tank, or how far down you zip your wet-suit jacket! Believe me, “too warm” is a much easier problem to solve underwater than “too cold.”

A common question people ask is, “Should I get a hot water system, or a dry-suit?” The answer to this lies in what you intend to do. I suggest having both systems available, depending upon your activity. For production dredging and sampling in extremely cold water, I would use a hot water system. For swimming across the river to stretch a rope, or for swimming down the river with mask and snorkel to look at the bottom in extremely cold water, I would recommend a dry-suit.

Other Things To Know About Cold Weather Dredging

If you are working in freezing temperatures above water, there are certain things that should be done on your dredge each day before knocking off. Your pump should have a drain plug tapped into the bottom. This way, you can drain the water at the end of each day to prevent your pump from freezing solid. It is not a bad idea to bring some hot water with you everyday in a thermos, because sometimes the pump will freeze even with the water drained. Be careful not to crack the pump housing by pouring too much scalding water directly over it when it is freezing cold.

Also, in freezing weather, the concentrates and water must be completely cleaned out of your recovery system at the end of each day. Otherwise, they will freeze solid and prevent the system from working until it thaws out the following day — if it thaws!

If you are not going to process them directly, your concentrates from the day should be stored well underwater to prevent them from freezing on the bank. Your mask, hood and gloves should be brought back to camp each evening and kept warm. Otherwise, you have the misery of putting them on when they are ice cold — unless you have a hot water system on your dredge.

Winter Dredging

Eric Bosch and author displaying nuggets pulled while diving together.

Dave and Eric holding nuggetsEven if you are able to handle most of the cold water problems with the use of good equipment, another factor winter dredgers often have to deal with is higher and faster water. While the higher water will allow you to mine further up on the edges of the river, in many areas it will prevent you from mining out in the faster and deeper water areas-which may provide easy mining during the summer months. If, due to the faster, higher water, you are not able to get out and sample in certain sections of the river, you will not be able to run a full testing program on that section of river; and you will miss pay-streaks. So, it can also be more difficult to locate deposits during the faster and higher water months of the year.

On the other hand, if the river edges are paying, the winter months may be the only time they are available for dredging. The location of deposits are going to vary from one place to the next.

While wet-suits, hot water suits and dry-suits do make for good insulation underwater, they generally provide poor insulation to the cold air above water when you are wet. Therefore, it is good to have a warm winter jacket to wear over your diving suit while taking breaks on the surface.

Tents in the snowAs a side note on this, my commercial dredging buddies and I ate many hurried lunches on deck during the winter months (even while it was snowing) while the dredge continued to run at operating speed (with a rock placed over the suction nozzle to slow the water in our recovery system), pumping warm water into our suits.

If you are mining in extremely cold conditions, it really helps to have a warm and comfortable camp. A person can put up with some pretty cold and miserable conditions if he or she knows there is a warm shower and hot meal coming later that evening. There are few things worse than freezing all day and then going back to stay in a wet and cold camp!

Author’s campsite during his first several years as a gold prospector.

How Tough Are You?

It takes a pretty tough person to dredge in extremely cold conditions. Even with the best equipment, there is still a substantial amount of cold water exposure on your hands and face. You spend quite a bit of time working on the dredge, tying off lines, swimming the river, cleaning up concentrates, making repairs, etc. This all adds up to exposure which can be painful or uncomfortable. Some people are gung-ho enough to dredge in extremely cold water on a short-term basis. Few people are willing to do it long-term.

We all have the potential to be tough enough to dredge in extremely cold water. What it always comes down to is whether or not we desire to be that tough! A lot of people think they are, and then realize they are not willing to do it!

Talk is cheap!

I was mining with several guys in 34-degree water one winter. One of the divers and I were sampling for a new deposit while the other two guys were actively dredging out a rich deposit we had already located. They were recovering several ounces of nugget-gold each day, while we were knocking out sample holes. One day, we helped get the production operation started and then headed out to do our sampling. We soon realized we forgot our lunch, turned around and drove back to where our partners were dredging. We had not been gone fifteen minutes, and they had already gotten out of the water and were in the truck with the heat turned on — drinking hot coffee! These were tough guys; that water was cold!

A partner and I were dredging in Alaska in October when things started to freeze. We’d had a very good season, but I wanted to put more ounces into my bottle before returning home. Ice had already formed on the edges of the river, and my partner had been ready to leave weeks before. I was determined to spend one more week dredging, because the gold was good and I had plans for what I was going to do with it. One day, with a week to go, I could not make my body go underwater again. “One, two, three, go!” — but my body refused. So, it just wasn’t worth it, anymore! I walked over and tugged on my partner’s air line and asked him if he was ready to go — home, that is. We were on the road later that afternoon in a warm truck with the heat blasting. In that area of Alaska, three feet of snow fell that night!

There is a point where the body just takes over and says, “No!” And, this is probably the point where it is smart for you to listen.

 

By Richard Doherty

“With the new instruments available today, millions of gold nuggets are within reach of the intelligent, properly equipped, electronic prospector.”

 

Hand full of beautiful gold nuggetsWhen I first heard about picking gold nuggets from the surface, or close to the surface of the ground, I really didn’t think it was feasible.

I made some halfhearted attempts at locating some of the precious yellow beauties with no success and much frustration. Finally, I buried a gold nugget down in the ground and attempted to locate it with my new detector. To my surprise, it wouldn’t detect the nugget, so I moved it closer to the surface and still couldn’t detect the target. It was almost on the surface by the time I was able to receive a very light audible signal. That did it! I quit!

Still, the idea of locating a gold nugget with an instrument really intrigued me, so I stayed in touch with the advances of metal detectors. In the meantime, I continued my more conventional prospecting activities in Arizona, where I was fortunate enough to associate with other prospectors who knew about gold deposition.

Years later, the metal detector industry began to develop detectors that would deal, at least somewhat, with the highly-mineralized ground associated with gold deposits. So I purchased one of the most advanced detectors on the market and went in hot pursuit of the elusive yellow nuggets. Hour after hour, I combed the ground; I searched everywhere the gold “had to be!” If it was there, I wasn’t finding it, so I pressed on.

Scorpion made from gold nuggetsFinally, after many, many frustrating hours, the first nugget succumbed to my detector, minutes later, another. I really got excited, and I decided to share this new-found activity with my friends. I helped them learn what I had learned, and then we developed new methods and techniques. Detectors were getting better, and I purchased the latest equipment, knowing that I needed every edge that I could possibly acquire.

We sorted out which instruments worked best and figured out how to get the most from the ones we decided to work with. Nuggets began to fall on a regular basis, and more friends became interested. We turned them on to the equipment we were using and the techniques we had developed. They began to find gold nuggets almost immediately. This surprised me; because after all the heartache I went through to locate my first nugget, my friends were quick to pick up what we had already learned.

Gold nugget hunting is not like coin hunting at all; it is a specialized field and requires specialized equipment and techniques. Once learned, it is easy. As you do it more and more, nuggets will yield to your detector more consistently.

First, there are three “musts” for any degree of success. Not one of them is any more or any less important than the others, because they are dependent upon each other:

1. The correct instruments must be selected. Selection is based upon the instrument’s performance relative to the size and purity of the gold and type of ground that will be searched.

2. Knowledge regarding the use of your instrument must be thorough.

3. Knowledge about where the gold is located. Most of this information is gathered through research and talking with others who already know.

Your degree of success depends upon how diligently each one of these three “musts” is followed, and it is that simple. If you decide to approach finding gold nuggets in this manner, it is not a matter of, “Will I find a gold nugget?” It is only a matter of when, how big, and how many!

Huge rough nuggetIt has never before been more possible to locate your own gold nuggets with the aid of a metal detector, than it is right now. It is not that there is more gold out there. In fact, each day, there is a little less. However, with the new instruments available today, millions upon millions of beautiful gold nuggets are now within easy reach of the intelligent, properly-equipped electronic prospector. You don’t need tons of equipment to haul around, nor do you need many thousands of dollars to get started. The exercise is mild; the air is fresh; and the pursuit of your own gold nuggets is done at your pace — no one else’s.

I would also like to mention some of the myths surrounding electronic prospecting. It is difficult to place these in any order, so I will just mention them according to the frequency of times I am asked:

“Are there still gold nuggets out there to be found?”

“Will a metal detector really find gold?”

“Didn’t the ‘old-timers’ get all the gold?”

“Why isn’t everybody doing it?”

“Isn’t all the land claimed up?”

“Don’t I need a specialized vehicle or mode of transportation to get to the gold?”

“Isn’t it hard work?”

“How can I find gold nuggets when I know nothing about geology, mining, mineralog, or electronics?”

“Won’t a detector find fool’s gold?”

Please don’t let these questions, objections or myths stop you from gathering your own gold. It’s a whole new exciting, profitable activity, and you can do it!

Public awareness is definitely on the increase, and hundreds are getting into the activity of capturing gold nuggets from the earth. There are pounds of gold being taken daily, and there is no reason why you cannot be taking your share!

Frustration and lack of confidence is the primary cause of failure. The reason most electronic prospectors fail is that they purchase inadequate equipment or don’t learn how to use it properly.

Hunting coins and hunting nuggets with a detector are quite different. Coins are a flat-sided target. Many nuggets are not. Also, many flat nuggets will slip sideways into a crack or crevice in the bedrock, which leaves very little target-area available from the surface. Shape, size, and lack of the “halo” effect can cause a gold nugget to remain a difficult target.

Of course, there are exceptions to this. Not too long ago, I found a 5/8-ounce gold nugget that was about one inch deep, lying flat. It sounded-off like a quarter! I was amazed to retrieve a beautiful nugget which was shaped like an eagle’s head!

Nugget hunters know how important good equipment is. I was speaking with a professional electronic prospector the other day, showing him a new detector. Before I could tell him what the detector cost, he said it didn’t matter anyway; because he was willing to spend any amount of money on the detector if it was significantly better than the one he was using. You see, he knows that good equipment will pay for itself, especially with the price of gold nuggets as they are.

I know coin hunters who dream of finding their first gold coin. Most never do. However, electronic prospectors, who follow the basic guidelines, will find hundreds of gold nuggets.

Where is the gold? This brings us to another reason why now is an excellent time to get started in this fascinating activity. There are clubs and various types of associations which you can join where you will meet other people who prospect. Some of these organizations provide mining properties for their members to prospect. The folks who run clubs are usually quite particular about the mining properties which they own, and they are also knowledgeable about which claims they should stake or purchase. One of the easiest and fastest ways to find gold is to join one of these clubs. Some even provide training programs or organize group mining projects where you can gain immediate, valuable hands-on experience. Talk with other members and the staff to gain information as to where you might begin your prospecting. This is the best way I know of to get started in any type of gold prospecting today.

As you prospect on these claims and talk with others, you will begin to get a “feel” for where the gold is and why it is there. Gold seems to be a lot easier to find if you already know it is there. If you are not sure, it could cause you to search halfheartedly, and that is not conducive for locating nuggets. You must know the gold is there; you must know how to operate your equipment; and you must know that your equipment will get the job done. If you have these three criteria well in hand, you will surely find your own gold. After that, it’s just a matter of spending some time doing it and improving your skills.

In the beginning, it may take you a minute or longer to recover a target you have established; but soon, these targets will be coming out of the ground so quickly that you will surprise yourself. My average recovery time per target is between fifteen and thirty seconds, depending upon digging conditions. I have seen it take as long as 30 minutes to extract a target, but these are more unusual conditions.

In Quartzsite (Arizona) last year, we had occasion to dig in some very old material that was as hard as concrete. This material had been deposited millions of years ago. There was no man-made metal present. But the gold was there! My detector sounded off, and we knew what it was; so we started to excavate. It was hammer and chisel time! You must be very careful not to scar the nugget, so digging has to be carefully-done. Almost 30 minutes later, out came a beauty. It weighed just over ½-ounce. It was detected under 13-inches of highly-mineralized, concreted earth and rock.

As you uncover a valid target, it will usually develop into a clearer signal or stay about the same. If it stays the same, you may also have passed over an area that is highly mineralized. Or perhaps there was some kind of hot fire in that spot during some time in the past. Sometimes, ashes will read very slightly on the detector. But the signal does not develop as you dig down on it.

If the signal disappears altogether, you have either moved the target, or you may have had a piece of rusting ferrous material that fell apart when you moved the soil. A magnet comes in handy to quickly isolate ferrous targets; it can be a real time saver!

Bullets, nails and other foreign metallic targets are some of the items you will learn to deal with. At first, they are nothing but a nuisance. However, let’s take a closer look at this: If you are digging metal of this nature, not only does it hone your recovery skills, but it tells you that the area has not already been searched-out (every smart, responsible detectorist has a container along to remove small metal trash-targets from the playing field).

If there are no previous dig-holes, you may be the first person to detect that area. But if there are dig-holes, and you are still finding metal, it tells you someone else did not do a thorough job. If they left trashy metal in the area because they were using an electronic discrimination mode, they certainly will have left nuggets behind, too! You will pick up the nuggets your predecessor left, because electronic discrimination seldom can be used effectively while nugget hunting. Only under certain conditions would you use discrimination, and that would be after many hours of experience. Even then, you could make costly mistakes. My advice is to not use electronic discrimination while hunting gold nuggets.

Meters, gauges, bells and whistles do not make a good nugget-hunting detector. I personally feel about the only function they serve to the nugget hunter is to add weight to the instrument — which is the last thing you need. Although I will admit that there are other good prospectors around who disagree with my opinion.

The following is a list of recommended reading material which may call for reading and re-reading. This is not a complete list, but the material suggested here is a must:

Willie Merrill wrote a book called, THOSE ELUSIVE NUGGETS; and he not only knows what he is talking about, he shares his knowledge in a very free manner. I have read the book no less than five times. Each time, I learn something new. Our minds are not always ready to accept all information the first or second time through.

Another book of importance is ELECTRONIC PROSPECTING by Roy Lagal and Charles Garrett, which will also require more than one reading. This book goes into the many avenues of electronic prospecting.

Any magazine articles written by successful electronic prospectors are definitely worth reading. Hundreds of articles could be written on the subject of electronic prospecting, and each one of them will have some hot tips for you. .

 
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This story first appeared in Gold & Treasure Hunter Magazine May/Jun, 1993 on Page 45. This issue is still available! Click here.

By Dave McCracken

Classification is necessary to increase the amount of smaller particles of gold that you will trap in your recovery system.

Dave Mack

 

It takes more water velocity to move larger-sized material than it does to move the smaller-sized material through a sluice box. Yet, to the degree that the water velocity over a sluice box is increased, there may be a loss of fine gold recovery. Or, to the degree the water velocity over a sluice box is slowed down, there is likely to be an increase in fine gold recovery–as long as there is still enough flow over the box to keep the riffles concentrating.

When larger rocks are pushed through a sluice box by water force, they also create greater turbulence behind the riffles as they pass over, which may cause an additional loss of fine gold.

To improve gold recovery, it is common practice to run material through a screen to classify out the larger rocks before running the material through the recovery-portion of a sluice box. In this way, less water velocity is needed through the box, which allows for a more orderly flow, and an increase in fine gold recovery. The action of screening materials is called “classification.” Materials which have been passed through a classification screen are called “classified materials.” The following video segment demonstrates this very important point:

The size and depth of riffles within a sluice box play an important part of this. A slower water flow might not keep a deeper riffle concentrating. A greater water flow can sometimes “boil-out” a lower-profile riffle. So as water flow is slowed down to catch finer-sized gold, it is generally necessary to use shorter riffles.

Half-inch mesh screen is commonly used for primary classification in small and medium-sized sluicing operations, because the screen is large enough to allow classification to take place quickly, yet no materials greater than half-inch in size will get into the sluice. Therefore a slower-velocity of water can be directed through the box, and fine gold recovery will be improved.

Classification for a sluicing operation can be done in any number of ways. One is to place a piece of strong half-inch mesh screen over a bucket, and shovel or pour through the screen into the bucket while sweeping the larger material off to the side. Once the bucket is filled with classified material, it can be poured into the sluice box at a uniform rate. It is better to not dump the whole bucket into the sluice all at once! This is because too much material is likely to overload the riffles and cause a loss of gold recovery.

In a situation where it is necessary to haul material a short distance to the sluice box, sometimes it is easiest to classify the material directly into a wheelbarrow and transfer only the classified material to the sluice.

Perhaps one of the best screening methods is to build a classification device that you can shovel into, and which will stand directly over the top of, and drop the classified materials into, the head of your sluice box.

The device should be built with the screen set at an angle. This way, larger material is helped to roll off of the screen as the pay-dirt is shoveled onto it. Smaller materials should fall through the screen and be directed into the head of your sluice box. This is actually a miniature model of the big classifiers used by large-scale heavy equipment bench-mining operations. A classification device such as this is rather easy and economical to build and will speed up a production-sluicing operation while screening is being done to improve gold recovery.

Any recovery system will only recover gold effectively down to a certain size-range. Most gold particles smaller in size than that will be lost with the tailings. Classification is one effective way of increasing the amount of gold that will be recovered out of the material that will be processed. As demonstrated in this following video segment, this is especially true of suction dredges; because dredges are able to increase the volume of production over other types of hand-mining activity.

Here is a substantial explanation of the system which we have developed to effectively recover more fine gold on our conventional suction dredges. It combines two classification screens to more-effectively separate material-feed into three size-fractions, each which is directed into a different recovery system. The smallest gold particles (which are most difficult to recover) are directed into low-profile riffles along the bottom of the sluice box which have long been proven to be very effective at trapping fine gold.

 

 

BY JUDE COLLEN KENDRICK

 

This is a picture that you will seldom see – me getting up at 5:30 a.m. full of excitement – to vacuum! Yet, I spent some of last summer and almost all of this past winter, doing just that. It wasn’t “dust bunnies” I was after, however; it was gold!

A few Decembers ago, I wrote a Christmas dry-washing article about the Mojave Desert. I said that I had made a portable vack machine to clean off the caliche (cement-like material) shelves that one encounters out in the desert. But it was not until last summer on the Klamath River near Happy Camp in California that I actually used the vack machine for what most people use them for, which is crevicing.

I knew about crevicing, of course, but it just wasn’t my thing. In fact, on several of my surface mining (motorized sluicing) trips there would be lots of prospectors around the creeks crevicing and getting gold. I cannot recall, though, at that time seeing anyone with a vack. They all had store-bought or homemade tools to get the gold out of all the nooks and crannies. On the Klamath, I borrowed a Mack-Vack made by Pro-Mack in Happy Camp, because I did not have the space to bring my motorized sluice along. My little portable vack that I had made was in the “equipment graveyard.” I had brought gad bars and digging tools, so I was set up to crevice. I will admit that I was not very enthusiastic about it at the time. I like to see dirt flying and lots of material running through my equipment. But it did not take long to change that lack of enthusiasm!

The bedrock around the area where I was on the Klamath broke apart fairly easily. I walked around trying to find the right kind of hard-packed gravel between the seams of these massive slabs. I had only used the vack for a while and had only about half of the 5-gallon bucket filled (not much material, I thought). Yet, when I panned it out, there was a beautiful match head-sized nugget. Now, this type of prospecting wasn’t bad at all!

Kay Tabbert and her husband Chuck, both members of The New 49’ers, were in the same area at the time. Chuck was busy dredging while Kay, with only her little hand tools, a whisk broom and dustpan, was crevicing on some bedrock not far downriver from me. All of a sudden I heard Kay calling for Chuck (and anyone else around). So I walked over to see what was going on. I could not believe it. Kay had separated a rock about the size of a melon, and in the crevice, stuck to one side, were 7 beautiful large flakes of gold! Just like that! I could not get back to my area fast enough!

I had dredged for years and I knew just how to spot the places where the water would deposit gold. It was really no different from working in the water – I just did not have to get my hair wet! I was feeling a little impatient, though, as I never did wait to fill up an entire 5-gallon bucket with material using the vack machine. But what I did pan produced great little “clinkers” of Klamath gold.

Unfortunately, I only had about seven days last summer up on the Klamath. But, I had five months this winter to play in the dirt. Lucky for me, I got “hooked” on vacuuming crevices!

I was prospecting Quartzsite, Arizona and the surrounding areas. The desert had a lot of rain this past summer and everyone was hoping that the washes would “pay off!” I decided to sell my beloved “Nick’s Nugget” dry-washer, as I knew I was going to be out prospecting alone a lot. As great as it was, it was too heavy and clumsy for me to manage on my own. I purchased a small dry-washer combo (with the vack option) from my friends Bob and Linda Taylor. This was great. One engine ran both and I could carry everything in one trip.

Hunting for bedrock in the desert is certainly not like on the rivers. It definitely does not expose itself as much. Yet in many places it is not deeply hidden. I was finding many places in washes where people had dug down to bedrock and had not even touched it with a whisk broom. So, guess what I did? They had already done the heavy work. I just sat there and vacked up the gold!

Finding new places to vack was not easy, as I have said. I have known for years, from experience, that the gold in the deserts isn’t always where it is supposed to be. What would look like great bedrock on the rivers often means nothing in the desert, mostly due to the lack of water volume and movement in the deserts. When I arrived at Quartzsite I met up with Al Powell, who is also a New 49’er member that I met briefly while on the Klamath. Al and I were finding “perfect” looking bedrock, in established gold areas, that produced nothing. We were always shocked, because all the “recipes” for gold were there. We could have found more gold in downtown Quartzsite! We were not giving up, however!

I decided to take five days and go off to find a hot spot for Al and me to work. I found a very small ravine below a heavily mined area that had a large section of bedrock exposed. It took two days of pulling “Buick-sized” rocks to work myself down to where I was getting some nice gold. After the fourth day, I showed Al my gold and took him out to the spot so we could clean it out together. Well, I suppose I did my job too well; as except for some small flecks, Al and I vacked all day and got nothing large. “OOPS! Sorry, Al!”

The weather in the desert turned nasty, with off and on heavy rains that went on for days. Consequently, all of the dry-washers around the desert were silenced. The ground in places was damp as deep as eight inches down, which forced people to grab their gold detectors and head out nugget-shooting until things dried out. Yet, Al and I were not held back; we were still out there, in a new area, with our vacks. We didn’t have any trouble bringing up the damp gravel, although the two of us looked like “mud pies” at the end of the day.

I had, from the beginning, been running my vack materials through my dry-washer so I would not have to pan as much concentrate. Even the damp material did not present much of a problem, as Al and I just ran everything through the dry-washer two or three times. I am sure that the people driving by during those wet days who saw the dry-washer running, said to themselves, “They are crazy!” Well, that is a whole other story, but we did have our pretty desert gold to look at all the way back to our desert “sanitarium!”

I would recommend purchasing a vack to anyone, even as a backup to your usual motorized sluice or dry-washer. And, now, when “housework” day comes each week, I won’t dread using the vacuum; I will just be practicing! Good Luck!

 

 

By Dave McCracken

Part Two – Sampling For Paystreaks

Dave Mack

 

There are few things in the world more enjoyable — and more exciting — than finding your own pay-streaks, particularly when they are rich! It is one thing if someone else turns you onto a previously-located deposit — which, by the way, you should always take when it is offered to you. It is much more emotionally satisfying when you locate a rich deposit by following the signs discovered by your own sampling program. Seeing the first flakes of gold uncovered, when you knew they were going to be there even before you saw them, is a wonderful feeling; it is a true thrill to follow those flakes into a rich deposit. There is nothing else like it! Some say there is no cure for gold fever.

The procedure for finding pay-streaks is quite simple, really. The key is having the emotional fortitude to follow through with your sampling procedure, by following up on positive signs if they are there. And remember, you don’t need to find a pay-streak in every sample hole. Otherwise, sampling would not be necessary. You only need to find a pay-streak once in a while to make mining pay off — on any scale.

As we discussed in part one, pay-streaks form in those sections of a riverbed where the water force slows down on a large scale during major flood storms. Because gold is so much heavier than other average streambed material in the river, particles, flakes and nuggets of gold tend to collect in these large, slower-moving sections of river, while the lighter materials continue to be washed downstream.

Pay-streaks can be large or small, depending upon the size of the low pressure (low velocity) area in the river and depending upon how much gold traveled through each particular area during major flood storms.

Here is a location on our mining property at K-15A during the 1997 flood

Here is the very same location at K-15A during normal summer flows.

Pay-streaks always form on the path that gold follows in the river. Sometimes there may be more than one gold path, because the gold may be originating in the river from several different sources.

Pay-streaks are very important to miners because they are larger than single-type deposits, such as those found in a bedrock crevice along the gold path. Therefore, pay-streaks are easier to find. Because they tend to be long and wide, pay-streaks are deposits which can be worked usually for quite some time.

Gold can be recovered from a pay-streak which is located on bedrock; it can also be found throughout the streambed material or on the top of a flood layer.

It is important to understand what flood layers are. They are separate strata of streambed, which were laid down by different storms or perhaps at different periods during the same storm. The various layers are usually very easy to distinguish from one other. Each has different colors and consistency, and the gravels are usually of different compact hardness. If you are looking for it, you can nearly always see the changes in flood layers as you dig or dredge a sample hole deeper into the streambed. Sometimes there is only one layer over the bedrock. Often there are two or more layers.

As we discussed in part one, gold is extremely heavy. Therefore, most gold travels along the bottom of the other suspended streambed material as it is being washed downriver during a major flood storm. If the material is washing down across bedrock, then gold can become trapped in the various irregularities, cracks and holes. Sometimes, if conditions allow, gold may even be deposited on top of smooth bedrock to form a pay-streak in a low pressure area of the river.

Sometimes, because the flood storm is not quite extreme enough to break up pre-existing hard-packed streambeds, material moving during a storm will wash over the top of already-established streambed layers, rather than across the bedrock. Therefore, newly-formed pay-streaks may be found on top of pre-existing streambed layers, rather than on bedrock.

It is very common to find pay-streaks on top of a streambed layer. Sometimes you can find pay-streaks on top of several different layers in the same location. Sometimes, you can find pay-streaks on a layer, but not on the bedrock in the same location.

Most gold-bearing rivers have some amount of gold disbursed throughout the streambed material, so you tend to recover a small amount of gold out of each sample hole. We call this “traces.” This usually is not very much gold; not enough to get very excited about and not enough to support a small-scale mining operation. It only takes a few sample holes to give you an idea of the average amount of gold that is disbursed in the general streambed. You can pretty-much expect to get this small amount of gold from each sample hole that you dredge or dig. If you recover more gold from a sample hole than is showing up in the average streambed, it is important to realize you are onto something — even if it is not exciting, yet.

Remember, sampling is the business of following positive signs into a pay-streak. When you are finding increased amounts of gold in an area, it is likely that you are onto the general gold path, and you are into a low pressure area of some magnitude. You may be very close to an excellent deposit.

So the first thing to do, once you start finding increased amounts of gold in a sample hole, is figure out exactly where it is coming from. Is it coming from a layer? This is really important to know.

Several years ago, I had a friend who was recovering two pennyweights (1/10th of an ounce) of gold per day with a 4-inch dredge, dredging in four feet of streambed material. He had been trained in the old school of thought, which says you always dredge to bedrock, no matter what. I jumped into his hole one day and noticed almost immediately that a lot of his gold was coming off the top of a flood layer which was located about six inches beneath the material’s surface. Investigating further, I found there was some gold coming off the bedrock, but it was not very much. About 95% of his gold was coming off that layer. Once I pointed it out, he began to just skim off the top foot of material, and he started recovering about five times as much gold. This is why it is important it is to establish exactly where the gold is coming from in a sample hole!

If you dig a sample hole through deep material and only find a marginal amount of gold, the location might still be worth working if you discover that the gold is coming from a layer change closer to the surface.

When I am dredging a sample hole and see a change in layers, I always slow down and uncover a section off the top of the new layer while careful1y looking for gold. If there is a substantial amount of gold on the layer, it is never hard to see if you are looking for it. All you have to do is hold the suction nozzle further away from the streambed material so there is just enough suction to pull the gravel, but not enough to pull the gold, which is about six times heavier. Underwater magnification makes the gold very easy to see. But you have to be looking for these changes in layers, and you need to slow down and look on top of them as they are being uncovered.

The gold is more difficult to see if you are digging up on the bank. In this case, layer changes can be sampled separately with the use of your gold pan or other recovery equipment.

Seeing an increase in the amount of gold in a sample hole, even if it is just a small increase, is one of the most important signs to recognize in sampling. You would not see the increase if you were not on the general gold path and on or near a low pressure location in the river. Seeing an increase in gold is always reason to investigate that location further, either by spreading the hole in different directions to see if it gets better, or by digging or dredging more sample holes in the immediate area. You should be acting like a dog who has found a nice, juicy scent!

As mentioned in part one, one of the biggest barriers new miners need to overcome is their own doubtful thoughts about how much gold they are not going to find in a sampling location. Many beginners have themselves talked out of finishing a sampling project long before they have properly completed it! Forget what you think might not be there, and just work hard to see what actually is there. This is what sampling is all about!

Time and time again, I have seen beginning miners start a sampling project, start recovering some gold which is not enough for their minimum requirements, but is far greater than the average amount of gold in the river; and then give the area up because it is not good enough. Afterwards, someone else will open up the same location a little more and find a rich pay-streak. Yet, the original miners are still sampling elsewhere, not having found a pay-streak of their own. Short of finding an acceptable pay-streak, a visible increase in the amount of gold recovered from a sample hole is the best sign you can look for. Don’t walk away from it until you are more than certain it is just a low-grade pay-streak which you have no interest in.

There is something mystical in the way gold affects people. This has been known for a long time. How much gold a person is finding, or not finding, definitely affects his or her emotions. Successful miners have learned to set the negative emotional impact aside and to use effective sampling techniques and hard work instead.

It has been well proven throughout history that gold is much easier to lose than it is to find. And, no doubt, men have walked away from more gold deposits than they have found due to the way they were emotionally affected by the results of their sampling operations.

I know of one man who dredged a sample hole and was recovering four-to-five pennyweights of gold per day. He spent a day pushing the hole towards the bank and discovered that someone had been there with a dredge ahead of him. He spent a day pushing the hole to the right and found the bedrock going deeper, but the gold was getting a little better and the pieces bigger. He decided the area was too difficult and not paying well enough, and went to sample elsewhere before he even came close to defining what kind of pay-streak he had located. What causes a person to give up so easily when the signs are so good? Why walk away from a location with fantastic signs to go sample a new location where you have not yet discovered any positive signs? The answer has to do with the way gold affects people’s emotions, and the fact that it is much easier to lose than it is to find!

There is an excellent lesson to learn from this: Watch for an increase in the amount of gold in your sample holes. Leave your negative emotions out of it. Follow up positive signs when you see them — always. Have some patience, and positive signs will lead you into the pay-streaks.

 

By Dave McCracken

Part Three – Sampling is a never-ending process

Dave McCracken

 

You would think that sampling could end once you’ve found a pay-streak. Because, once you’ve found a pay-streak, you start your production operation to recover the gold. However, sampling continues on, possibly even to a greater degree, even after you’ve located a rich deposit.

When you locate a deposit that you have determined is good enough to work, your next step is to define your deposit’s boundaries. This takes more sampling. It is generally done by dredging or digging more sample holes. The first and most important boundary you should find, especially if you are dredging, is the lower-end, meaning the downstream-end of the pay-streak. This is because you need to find a place to drop your tailings where they will not end up on top of your gold deposit.

In mining activities of any kind, tailings placement is of primary concern right from the beginning of the operation. You generally do not worry about it too much during sampling, because you have not determined there is a deposit in the immediate location as yet. But as soon as you are certain there is a deposit worth developing, where you place your tailings becomes very important!

In dredging, providing you are going to have the time to develop the entire deposit, you usually back your dredge further down river, dredging sample holes as you go, to locate where the deposit plays out. It is then smart to dredge a few more sample holes below this point to make sure the deposit really did play out where you will put your tailings. Then, start dredging from the tail-end of the deposit, dropping your tailings over the area that you have already worked.

As you work the deposit forward, you also must locate the left and right boundaries of the deposit. This also requires your sampling attention, only in a different way. Rather than dredge or dig sample holes, pay close attention to how much gold you are recovering while continuing to move your production hole in the direction of each side of the deposit. In dredging, if you are into a healthy deposit, you will see gold when you uncover the strata of streambed material where it is located.

As I mentioned in the earlier parts of this series, when you find gold in a sample hole, the first thing to do is establish where it is coming from. Is it from the contact zones between streambed layers or is it coming off the bedrock? This also applies to production mining. You need to know where the gold is coming from so you can watch that particular strata of streambed material closely to make sure it is still paying as you move your production hole forward and toward the left and right side boundaries of the deposit.

In dredging, if it is a good pay-streak, when the paying strata is uncovered, you can actually see the gold if you slow down and look. You will also see the gold disappear once you extend beyond the boundaries of your pay-streak. It is standard practice to slow down and watch your pay strata closely when production dredging. By following this procedure, you will continue to dredge up pay-dirt with a minimum of non-paying material. This means that the job of sampling never really ends, even when you are mining a good pay-streak; especially when mining a good pay-streak!

When digging, as in high-banking, you cannot depend as much on seeing your gold as you dig in the pay strata, so it can be necessary to clean-up your recovery system more frequently to make sure you are still mining in a section of the gold deposit. You can also sample the pay strata with a gold pan on a regular basis to make sure it is still paying in sufficient quantities.

The idea behind a production operation is to mine all of the deposit, while mining as little of the non-paying material outside the deposit as possible. However, you cannot always directly see where the deposit plays out. So you must be constantly watching how well the deposit is paying and where it seems to play out. This can sometimes be difficult to do; because some pay-streaks are not entirely consistent. For example, a non-visible obstruction or change in the bedrock upstream can cause an entire section of pay-streak deposit to boil out and give you the false impression of a boundary–when there might be an even richer section of the pay-streak several feet beyond where it apparently plays out! This has happened to me a number of times when I discovered further upstream that the pay-streak was wider than I thought. Then I had to drop back and pick up what I had missed on my first pass.

Keeping these thoughts in mind, just do your best to figure out what the deposit is doing as you follow it. Every once in a while, it is important to devote some time and energy continuing to sample beyond the apparent boundaries of the pay-streak to make sure you are not missing anything important.

Short of actually finding a rich pay-streak, finding an increase in the amount of gold in a sample hole is the best sign to look for while testing. Finding an increase in gold means more sampling is a good idea in the immediate area.

In the same way, finding a rich pay-streak means much more sampling is justified in that immediate area–especially beyond the apparent boundaries of the pay-streak you are working. This sampling is best done as you move forward, before you start dumping your tailings in that location.

Another important thing is to determine for yourself how much gold you actually need to recover on a daily basis to make it worth your while to work the deposit. Sometimes there is a big difference between what a person says he or she must recover and what a person will accept in order to remain in a deposit. You should be honest with yourself about this. If you need to recover five pennyweight a day, then you should not be production mining in a deposit which is paying only one pennyweight a day, unless you have some reason to believe it is going to improve right away. Also, if five pennyweight a day is your acceptable level, you should discipline yourself to mine the lower-grade gravel on the boundary-edge of a pay-streak if it is paying this much or more, no matter how much more the higher-grade section of the gold deposit is paying.

Some pay-streaks have a richer portion in the center or along one edge, and a lower-grade section throughout the remainder, which still may be high-grade enough to work by your own standards. Yet, you will find yourself much more interested in recovering the gold out of the rich section, because it is more exciting as you uncover all that gold. It takes personal discipline to work all of the acceptable portions of the pay-streak, when only one portion is extremely high-grade. I have seen many deposits (some of them my own) wasted by miners moving forward, dredging only the high-grade, while dumping tailings on the lower grade–but still acceptable–portions of the pay-streak. We all learn through hard-won experience just how valuable pay-streaks are once they are located, and how important it is to production-mine them in a disciplined and orderly manner, wasting as little as possible

There is an old maxim which always seems to be true: If you are looking for easy gold, go where others have already found it, and look beneath the area in which they started laying down their tailings! People get so excited when first discovering a deposit, they usually don’t think much about what they are dumping their tailings on top of until it is far too late!

The main point I have been trying to make here is that sampling really never ends. When you are not in a deposit, you will find yourself sampling to find one. When you find one, if you are wise, you will constantly sample to keep yourself within the boundaries of the deposit. Then, you’ll need to sample again to find another pay-streak in the immediate area once the first one runs out. Sampling basically is your procedure to acquire the necessary perception of where the gold is so you can recover as much as possible for your efforts. This is why you want to be good at it.

Don’t quit!

 

By Dave McCracken

Part One – The Fundamentals

Dave Mack

 

During the Group Mining Projects we conduct each season, I always like to start by discussing the most important and fundamental ingredient in successful gold mining. That basic ingredient is you, yourself!

You are the one who makes decisions for yourself. You decided to get into mining in the first place. You also make the decisions on how you are going to approach gold mining, and how you are going to deal with all of the problems and the barriers to your success. Regardless of suggestions or input you receive from others, you make the final decisions on what you are going to do-no matter what they are.

The main problem in gold mining is in overcoming unknowns. Until you find them, you do not usually know where the good gold deposits are located. If it were really easy, all the gold would already be gone. The fact that so much gold is being recovered by small-scale miners today proves it was not easy to find in the first place. Otherwise, the old-timers would have found it all!

True, it is much easier for us now than it was for them. We have low-cost modern equipment they never even dreamed of! Accessibility to gold-bearing areas is excellent. We have new technology as well as the benefit of the technology developed by the old-timers. We also have historical information that directs us to the proven gold-bearing locations. The old-timers had it much more difficult than we do. But, it is still not that easy. When you get out into the field, you are mainly faced with not knowing where the gold is! And, this is where it comes down to you and your ability to overcome problems and the unknown.

Gold mining procedure is very simple. And there is an enormous amount of gold still accessible to the small-scale miner. The problem you face is not knowing exactly where it is. It can be six inches beneath where you’re standing or where you are digging, and you will have no idea it is there for sure until you find it!

You live by every decision you make. If you decide in your own mind there is no gold in an area or on a claim, you are probably not going to prospect that area, unless you change your mind. It is important to avoid making decisions that are not based upon solid observation. A miner on any scale must be an investigator, a hound dog on a tricky trail. Good investigators never rule out possibilities before their time.

Successful gold mining is generally done in two steps: First is sampling or prospecting, and then, production.

While some gold-bearing creeks and rivers tend to have gold values dispersed throughout their entire streambeds, there is generally not enough gold to make a small-scale mining operation payoff very well. Because we are limited as to how much gravel we can process as small-scale miners, we need to find higher-grade deposits. This means we need to look for them, and this is where sampling comes in.

When my partners and I first started gold dredging, we made the mistake of putting our dredge into a likely spot and dredging in that same location for about 30 days, even though we were not getting very much gold. We had in our minds that we had to keep going because we just might uncover a bonanza at any time. While that may have been possible, we would have had to be very lucky to find a rich deposit this way.

Because gold is so heavy — about six times heavier than other average materials found in a streambed, such as rock, sand and silt –it tends to follow a certain path when being moved in a river. This path generally runs from inside bend to inside bend (when the waterway is running at flood stage), and in a meandering line between the bends. Gold deposits are sometimes found elsewhere, but the statistics of history show that most recovered deposits have been located along these paths.

This is a very important bit of information; it provides you with a good idea of where to start your sampling. You can rule out about 90% of the riverbed at the start, and concentrate your sampling efforts along the path where you are most likely to locate an acceptable gold deposit.

Let’s define a few basics: “Bedrock” is the solid hard rock of the earth’s crust–like a cliff or like the solid rock you see in highway road-cuts through the mountains. “Streambed” consists of all of the rocks, sand, silt, gold, and other sediments that end up in the bottom of a creek or river. Streambed always lies on top of bedrock. A “lode” gold deposit is gold that is still locked up in solid rock, often contained in quartz veins. “Placer” gold deposits are created after erosion has broken the gold away from the lode and deposited it elsewhere. There are different kinds of placer deposits. The difference primarily has to do with how far away from the original lode the gold has traveled.

Hidden irregularities on the bedrock channel of a river can change where the gold path runs. So, until you locate the gold path, you are never certain where it is going to be. But inside bend to inside bend (during flood stage), and a meandering line between inside bends, is a good place to start your sampling. I have seen some gold paths located off this line, so you have to be flexible. But this is what sampling is all about. Sampling is done by digging or dredging test holes in different locations, comparing one against the next, establishing where the better results are coming from, and following those positive signs until you locate an acceptable deposit.

Most gold-bearing rivers have a certain amount of low-grade gold values dispersed throughout the gravel. The general gold path tends to have more gold along it than the average gravel throughout the rest of the river. You also generally find more iron and other heavy elements along the gold path.

When making test holes, keep track of the amount of iron, iron objects, and gold that you recover from each hole. After you have completed a number of holes, you will start to get an idea of the average gold values and other heavy materials in the riverbed. Then, when you turn up more than the average amount in a test hole, it is a sign that you have located the gold path. Sometimes, there is little visible increase in gold, but there is a visible increase in the amount of iron rocks, pieces of lead, and old rusty objects.

There is a certain amount of microscopic-sized gold moving downstream in some rivers at all times. However, gold that is large enough for us to recover with our small-scale mining equipment generally does not move in a riverbed to a large extent, except during major flood storms. Storms of this magnitude are able to generate enough water force and turbulence to get all or most of the streambed material flowing down the riverbed along with the water.

Because gold is so heavy, when being washed downstream, it quickly works its way to the bottom of the other materials being washed along with it. The gold also moves more slowly. Cracks, crevices, holes and barriers in the bedrock can trap the gold out of the flow of water and material. And of course, this happens much more along the general gold path than off of it.

Gold deposits along the general gold path can be small or large, depending upon the size of the gold trap. The most important type of gold trap in river mining is called the “pay-streak”. Pay-streaks always form along the gold path where the river’s flow slows down on a large scale during a major flood storm. One example is the tail end of an inside bend in a river. Centrifugal force places most of the water pressure to the outside of the bend, leaving a low-pressure (low-velocity) area at the tail end of the inside bend. This is a very common location in gold-bearing rivers to find pay-streaks.

Another example is where the river slows down after a long stretch of faster water. Anywhere along the general gold path where the river slows down on a large scale during a major flood storm is a likely spot to find pay-streaks.

Pay-streaks are important because they are large deposits as opposed to smaller, single-type deposits–like what you might find in a bedrock crevice along the general gold path. The size and richness of a pay-streak depends upon the size of the low-pressure (low-velocity) area created in the river, and on how much gold traveled through that section of the river during the flood storms which formed the deposit.

Most pay-streaks have definite left and right outside boundaries, meaning the gold tends to run out quickly once you get outside the pay-streak. Sometimes upstream and downstream boundaries are not so easy to distinguish. Varying water flow turbulence during major storms can sometimes make a pay-streak somewhat inconsistent. It may appear to be good for a while, bad for a while, and then good again, but the outside left and right boundaries tend to hold true most of the time.

Because pay-streaks have some size to them, they are much easier to find than single-type deposits while sampling. Most successful river miners use the following technique to locate and recover pay-streaks: First, locate a proven gold producing section of the river. By digging or dredging sample holes, locate the main gold path. More sample holes are continued along the path until a pay-streak is located.

This method is generally used whether the operation uses gold dredges in the river, sluices, or even heavy equipment up on the bank. Since the bank consists of older streambeds left high and dry, you are just as likely to find pay-streaks on the bank, or in the ancient streambeds further away, as you are in the river itself. If you are able to find acceptable amounts of gold in a riverbed and you want to find more, look upstream and downstream along the same line of flow in the riverbed. Keep in mind the direction water and material would be moving in a major storm. Gold generally will have moved in the same direction as the water flow.

The point about locating a proven gold-producing section of river is really important! You can save yourself a lot of time and energy by finding out where other miners are already doing well. If somebody has located a pay-streak, there will almost always be more pay-streaks in that general area of the river.

Investigation to locate proven areas, and communication with local successful miners to find out where deposits have been located, can save a great deal of sampling time. All of the really successful small-scale miners I know make it their business to stay updated on who is finding deposits and where.

The overall process of successful mining is quite simple. We have it down to a science, having taken most of the chance out of it. Gold travels and deposits along special lines. A knowledgeable, energetic, persistent sampling effort is assured of always finding the next pay-streak.

Sound simple? It isn’t that easy! This is because you never know where the next deposit is or how long it is going to take to find it. And, this is why it always comes back down to that important, fundamental ingredient, which is you!

You are the one who decides where to put your sample holes, how large to make them, and how long to continue them. You are also the one who evaluates the test results and has to decide what to do next. You have to decide, based upon your sampling results and the other information you have collected, whether a certain section of river deserves further sampling activity or if you should move on to another location. Every decision you make is a crossroads that will directly affect the final outcome.

It is important to realize that how much gold you get from your mining activity depends entirely on you and what you decide to do. A good miner is an investigator who tracks down where the gold is coming from, and diligently works his or her way right into it. How good you are does not depend upon how much time you have spent at it in the past. It depends upon how much you really want to succeed and how willing you are to hustle yourself into a deposit.

I know of quite a few people who have discovered rich gold deposits in their first season. I also know a lot of guys who have been at it for years, and still cannot seem to find acceptable deposits for themselves. Why is this? They are not sticking to the right procedure. They are making the wrong decisions, and, a lot of the time, they are (deciding to) giving up too easily.

Again, the main problem is not knowing. So, based on the information you do have, you are constantly being put to the test, having to decide if the gold is likely to be in a certain area or if it is more likely not to be.

People who have the most trouble in gold mining are the ones who give up too easily. You need to give your sample holes a little more time and effort than they deserve, but without overdoing it. This is a matter of judgment which gets a little easier with experience. It’s always going to be a challenge, though; because you don’t know if the gold is going to be there right up until the point when you find it!

Once you find a good deposit, it is easy to see why it is located there, and you will also see how easy it was to find. But when it runs out, you are right back to not knowing where the next one is going to be. Gold mining is always an emotional challenge.

The problem most people have with mining and sampling has little to do with judgment in sampling. It has to do with other basic decisions they have already made concerning their own personal success. It is very difficult to help someone become a successful miner when that person has already decided he or she is not going to do very well at it. Some people work at it just a little bit, and then give up on their sample holes long before they are completed. You cannot find gold deposits this way unless you are awfully lucky. This is good food for thought for everyone.

Some people get into gold mining as a get-rich-quick solution to other problems they have created in their lives. Any person who is giving up or quitting in their personal life hasn’t much chance of succeeding at gold mining!

If you are not finding enough gold, you cannot blame the claim, the river, the club you belong to, or anything else. Blaming an outside source might make your ego feel better, but it will not help you locate more gold. You are either getting it, or you are not. Blaming anyone or anything else is going in the wrong direction. The answer is to become effective, communicate with other miners to find out where the gold is coming from, and then get busy with your sampling. If you want to do well in gold mining, you have to make it happen!

And, if you are not sure if you have given a sample hole everything it deserves, be honest with yourself about it and give it a little more. It takes personal discipline to be a good sampler!

This is not to say that gold mining cannot be fun. It is a great outdoor activity no matter how much gold you find while you are prospecting for high-grade deposits. Once you get involved though, you will find it is more fun if you are finding more gold! If you are looking for challenge in your life, if you want to put yourself to the real test, then gold mining is just the thing for you!

When you are producing sample holes and not finding acceptable amounts of gold, when you are not sure where the gold might be, and you are not sure exactly how to deal with it, that is when you are put to the real personal test. This is when you have the opportunity to see who you really are and where your personal improvement lies. There is not a successful miner alive who does not have to deal with this on a continuing basis! This is why it always comes back to you. If you are strong enough to pull yourself through it, you will learn to sample, enjoy new thrills, and attain personal achievement and growth, not to mention the gold you will find.

There is much, much more to know about the business of sampling, which we will continue to cover in future articles. But we have covered the most important and fundamental ingredient here. If you can get yourself squared away with the right attitude, and approach mining with a stiff upper lip and the eye of a tiger, you will have no trouble figuring out the rest!

Don’t quit!

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