By George Anderson

Prospecting around and enjoying the New 49’er properties near Happy Camp in northern California!

 

 

Last winter my partner and I devoted our two-week-long vacation to gold prospecting. We enjoyed our time exploring some New 49’ers Mining Club claims, in the beautiful Mountains of Siskiyou County in northern California. We panned for gold, dug out crevices in rocks that “old-timers” missed, hunted for nuggets with metal detectors (“nugget-shooting,”) and surface-sluiced some virgin placer material!

The New 49’ers Mining Club has around 60 linear miles of mining claims on the famous gold-rich Klamath River and its tributaries, including the Scott River, Salmon River, Elk Creek, Indian Creek, and others.

Our objective on this trip was to locate promising stretches of river to gold dredge this next summer. We also “scouted” easy access points and comfortable, enjoyable campsites. The rivers and creeks were running fast and high, making it easy to identify the low pressure areas, like back eddies, that allow placer gold deposits to form. We quickly found more highly promising stretches of river to mine than we could ever hope to dredge in a hundred lifetimes!

The first couple of days we did some surface-sluicing behind a huge boulder on the west bank of the world famous Scott River. We found a few small nuggets (“pickers”) in our first small sample hole. We averaged about 10 to 15 gold flakes in each pan. That was pretty good, since we’d only mined a couple of yards of material and weren’t on bedrock! But, we wanted more gold!

Moving upriver, we located a large bedrock outcropping with a two-foot ledge that extended into the bank at least six feet. This bedrock was smooth; it was old river channel! A very good place for placer gold to deposit! So we set up our sluice there, and started following this bedrock across the surface of the streambed. My partner soon found a nice nugget in the header-box of our sluice. I cannot tell you how excited we got, because we hadn’t even dug three feet! Some nice little nuggets (“pickers”) were visible in front of the first riffle. Panning the material from the sluice box averaged around ten thick golden flakes to the pan. This gold was a little more coarse (i.e. “chunky,”) than the gold from the first sample hole. We worked on this ledge a couple more days, finding some really nice gold, before deciding to sample another area.

Nuggets weighing many pounds have been found on the New 49’er claims along the Scott River and in the immediate surrounding locations. That’s the reason we wanted to use our metal detectors!

However, even though we went to some old hydraulic mining tailings high above the Scott River, we were only able to find nails, foil, hot- rocks, an old shovel and a horseshoe; not quite the large nuggets that we know are “out-there” still waiting to be found! Don’t worry; we will be back!

It rained again the next day. So we decided to set up our sluice on a tributary of the South Fork of Indian Creek. We knew several members of the New 49’ers Mining Club had previously done very well on this creek.

After looking around a bit, we located their workplace a short distance from the road. Starting where they had left off, we soon encountered extremely hard-packed gravel. This made digging pretty slow and difficult. We used picks and six-foot steel bars to break up the gravel before running it through the sluice. We mined this site slightly more than a day, recovering a few nuggets and approximately five nice golden flakes to the pan while cleaning up.

Cleaning up the sluice every hour told us if we were on the right track. After a while, we felt we should move to better ground. During the rest of the second day, we drove up the South Fork of Indian Creek, looking for access roads. We encountered snow towards the top of the mountains. About four inches fell the night before. Driving down steep access roads in the snow did not seem wise, so we didn’t have the opportunity to prospect the New 49’er Indian Creek claims as much as we had hoped. We plan to get back up there this summer and really take a look!

Rain fell pretty steadily the next few days. We scouted out claims on the Klamath River, while crevicing and “nugget shooting,” One afternoon, in between rain showers, we stopped on K-21 just below the bridge over the Klamath River in Happy Camp. My partner pulled a clump of roots out of a crack in the bedrock. We couldn’t believe our eyes! It easily produced the richest pan of gold either of us have ever seen! I’ll bet that there were at least 50 gold “colors” in that one pan! I thought, after seeing that pan: How much more can we find with a dredge or motorized sluice? We definitely plan to mine this particular spot in the future!

Only one more day to play! We decided to check out the New 49’er claims on Elk Creek. The main road into the area was passable, “one-lane” in some spots. But it wasn’t too bad, considering the extent of the previous year’s flooding. We found a lot of good access roads and excellent camping locations along Elk Creek. A deep pool, just downstream from a high-pressure area, looked very good! Elk Creek has a very rich gold mining history, and I am looking forward to spending some quality time dredging here this summer.

Winter is a good time to go prospecting; it is a sure cure for cabin fever. You have the whole country to yourself at this time of year, because there is hardly anyone around. We did not see a single person on the river or creeks that we visited. Water is high enough that it is possible to prospect (pan or surface sluice) locations that are normally dry. Mosquitoes and flies are very “low-profile” during the winter. We did not see any! Perhaps most important of all, the high water allows you to see where the gold is being deposited, since you can actually see the water in flood conditions.

Go prepared! A good rain suit, hat, gloves, and rubber boots are essential, if you plan to work in the rain. I’ll bet that it rained 12 of the 14 winter-days we spent on the Klamath River in Northern California. When you have got gold fever” as much as my partner and I do, a little rain won’t stop you from doing what you enjoy most in life; prospecting and finding gold!

 

By Dave McCracken

To recover finer gold more efficiently, it is necessary to direct finer-sized materials into more-shallow riffles, that require milder water flows to keep them functioning when filled with concentrated material.

Dave McCracken

 

In gold mining, when we talk about gravity-recovery systems (as opposed to chemical-recovery systems), we are basically talking about the creation of a suspended medium. A suspended medium is a condition of fluidity where materials are allowed to separate because of their relative weights.

Since gold is around six times heavier than the average of other materials which make up a streambed, if you pass raw streambed material through the right kind of suspended medium, you are able to drop the gold to the bottom, and direct the lighter materials off the top as tailings.

As an example of this, if you dropped some gold onto the hard ground, even though the gold is much heavier than the material making up the ground, because the ground is somewhat hard and compacted, it would probably take a very long time for the gold to work its way through to the bottom of the material in that compacted state.

But if you dug up all that ground (and gold), and dumped it into a raging river during a major flood storm, the material would all get churned into a liquid slurry as it is washed downstream in the river, and the gold would very quickly work its way down through to the bottom of the slurry. This is because the slurry is in a liquefied state of suspension, where heavier particles can easily penetrate downward, because gravity is pulling on them much harder than the lighter materials.

There are different ways to create suspended mediums so that gold can be recovered from streambed materials. Mechanical jigs create a pulsating medium within a chamber that keeps water and material in a state of fluid suspension. Oscillating sluices create a left and right movement (similar to panning) as material is washed over top by a mild flow of water. Shaker tables use a finely-tuned vibrating action, with a very mild flow of water, to separate material by weight. Because these systems use mechanics to help keep or create a suspended medium, we refer to them as “mechanical recovery systems.”

Most recovery systems on suction dredges use fixed riffles to trap gold out of lighter streambed materials as they are washed through a sluice box by a flow of water. Riffles are baffle-like obstructions, fixed in place along the bottom of the sluice box. They are designed and positioned so that there is a back-pressure created that sucks water and material behind the riffles from the flow over top. When the correct water-flow is directed over a riffle, the back pressure keeps the area just behind the riffle in a state of continuous fluid suspension. This creates a medium where the heaviest material (gold) is allowed to concentrate.

Gold recovery systems that use a flow of water over riffles are called “fixed recovery systems.”

Classification (sizing of material) is the key to fine gold recovery. This is true in both fixed and mechanical-type recovery systems. In general terms, this means that the finer (smaller) in size that you want to recover gold efficiently, the more closely the material must be sized, and the more finely-tuned the suspended medium must be to facilitate the separation.

As an example to put this in perspective, the water flow it would take to move a 5-inch (diameter) rock will likely be violent enough to wash away a fine particle of gold. And vise-versa: A suspended medium tuned so gentle as to allow fine particles of gold to efficiently separate from lighter streambed materials would be completely overwhelmed by a 5-inch rock.

The general idea is that if you want to efficiently recover finer-sized gold, you have to first separate it from larger-sized material. This is accomplished by screening. The process of screening is called “classification.” Classified material(s) can then be directed into a recovery system that has slower water and more gentle suspended medium(s).

What do I mean by a “gentler suspended medium?” In this discussion, I am mainly talking about the size of riffles. Because, the bigger (deeper) the riffle, the greater (and more violent) water-flow required to maintain a suspended medium of water and material behind the riffle.

Let’s talk a little about what happens behind the riffle in a sluice box. If you only run water over the box, it does not take very much water-flow to maintain fluid movement behind the riffle, because there is nothing solid to obstruct the flow. But the average streambed material (rocks, gravel and sand) weighs around 4 times more than water. This means water-flow and turbulence must be dramatically increased to keep material in a suspended state behind a riffle. The deeper the riffle, the greater the volume and weight of material which must remain suspended – so the greater the water force (and violence) needed to keep a riffle from packing up.

What is “packing up?” That is when you overwhelm a riffle with too much weight of material (rocks, sand, silt), and the suspended medium is lost. When the suspended medium is lost, most of the riffle will no longer concentrate the heaviest materials as they are washed over the sluice box.

Keep in mind that when a riffle is operating correctly, it will continue to concentrate the heaviest materials that are passed through the suspended medium.

At the beginning of a production-run, the specific gravity of the average material behind a riffle will be similar to the average specific gravity of the raw material found in the streambed. For the purposes if this discussion, let’s say this is around 4 times the weight of water. But as other heavier materials like iron (specific gravity of around 8) flow into the riffles, the heavier materials will displace lighter materials, and the materials behind the riffle (called “concentrates”) will become heavier. Each area is different, but it generally does not take long to accumulate concentrates in a sluice box that are around twice as heavy as the average raw material being processed. Heavier materials are usually associated with iron, and dark-colored by nature. These are often referred to as “black sands.”

The heavier the concentrate behind a riffle, the more water-flow and turbulence is required to maintain a suspended medium. The deeper the riffle, the more it will become overwhelmed by the increased accumulation of heavy material. So a deeper riffle requires a faster, more violent flow to keep it working as the concentrated material behind the riffle becomes heavier.

On the other hand, the shallower the riffle, the less water-force it takes to maintain a suspended medium behind the riffle. Less water force and violence will allow smaller particles of gold to settle.

But a shallow riffle also requires that the water flow be reduced. This is because a shallow riffle will not create enough protection behind it to prevent turbulent flows from boiling fine gold away. What do I mean by “boiling?” I mean that if you put too much water-flow over top of any riffle, the suspended medium becomes so violent that even the heaviest particles can be washed away.

Here is what I am saying: If you want to recover finer gold more efficiently, then it is necessary to direct finer-sized materials into more-shallow riffles, that require milder water flows to keep them functioning when filled with concentrated material.

But the problem with suction dredges is that we are sucking up a lot of rocks! Let’s just use the example of a 5-inch dredge. The nozzle-restriction will allow a 4.5-inch rock to be sucked up into the sluice box. And there must be enough water-flow through the sluice to keep the 4.5-inch rocks, and everything else that is being sucked up, flowing through and out as tailings. Otherwise, the material will build up on the dredge and sink it in very short order!

So initially, we are dealing with a water-force through the sluice box that will wash 4.5-inck rocks all the way through. That is a lot of force. And the force is turbulent.

Part of the reason why a rock is moved by a water-flow is because it is being pushed along by the water. A nearly-equal reason is that it is also being pulled along by the vacuum that is created behind the rock as the water flows around it. The vacuum behind a rock creates enormous turbulence that will affect anything it comes in contact with – including small particles of gold. The turbulence associated with the movement of a 4.5-inch rock is a lot, compared to the mild state of suspension necessary to allow a fine-sized particle of gold to settle behind a short riffle.

Since we must suck up rocks in dredging, the bigger rock we can suck up, the fewer we have to move out of the way by hand. Therefore, the first priority in the recovery system is to separate the big rocks away from where we want to recover the fine-sized gold. We do this by dropping the smaller-sized materials through a classification screen, and then directing them into slower-moving recovery systems. Sometimes, we are even able to screen two different sized products, and direct each into a separate recovery system, where the suspended mediums can be adjusted accordingly.

But the one mistake I often see is that the pre-sized materials are usually being directed into slower-moving recovery systems that are using deep riffles. As these riffles do not have enough water-flow directed over them to create the required suspended medium, they pack up and don’t work very well. What I mean by this is that most of the space behind a larger riffle can pack up. Sometimes it is only the surface area behind a big riffle that is working, while the rest of the area behind the riffle is packed solid.

Bigger is not better when it comes to riffles in a fine-gold recovery system. In fact, it can be worse.

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.

Here are some things to look for to get a better idea if a riffle is working for you:

  

 

1) The material behind a riffle should be visibly dancing during normal operation. You should be able to see that all of the material there is in a continuous state of vibration and movement. This can be deceiving, however. Because sometimes, only the surface of the material behind a riffle is in movement. Everything under the surface can often be packed up.

This is almost certainly the case; if after you shut down, you scrape behind the riffle and find that just below the surface of black sand, it is all packed up with lighter, blond-colored material. In this case, you will have to decide if you need to increase the water flow and violence (which will make it harder to settle fine gold) or shorten the riffle.

Shortening the riffle is usually the best solution.

Please don’t get me wrong here. I am not talking about the riffles that get big rocks passed over top of them. I am talking about the riffles where you direct pre-sized, smaller material.

2) Do some controlled tests at production-speed (meaning while someone is sucking material into the dredge’s suction nozzle or feeding material into a sluice), while feeding a pre-weighed amount of fine-gold into the system. You can either catch and test the tailings, or you can process the gold from the recovery system (or both), to evaluate how well your recovery system is working.

Here is where you can buy panning ore which contains fine gold.

If you are losing gold from a fixed recovery system, it will come down to either a screening system that is not working very well (to separate the fine gold from the big rocks that must be washed away using heavy force), or a bad relationship between the flow of water and depth of riffles in the fine-gold recovery system.

The answer is to just keep working at it until you get it right.

Okay; so, if bigger and deeper riffles are not the answer to recovering fine-gold from pre-sized material, how small and shallow should you go? Weight and shape-characteristics of the average streambed material in each area may be a little different. For example, crystalline, angular-type material requires more force and turbulence to keep it moving along. So there is not a fixed answer that will work perfectly in every single situation.

However, as a general guideline, I would say that the depth of a riffle should not be much more than the maximum size of material that is being directed there. In other words, if a 3/8-inch screen is being used to pre-size material, you probably don’t want to use riffles much deeper than 3/8-inches. Then you set the water-flow to keep those riffles fluid when there is an accumulation of concentrated material behind them. This is not a fixed formula. You will have to use your own best judgment to dial it in right based upon your local conditions.

Remember: If you use shorter riffles, you must slow down the flow over top of them to keep from boiling-out your fine gold. Slower water, and less violence, allows for finer particles of gold to settle – as long as a suspended medium is maintained behind the riffle. If you can keep the black sand in movement, without boiling out the riffles, you will have a great recovery system. Because gold is around 2.5-times heavier than iron, fine particles of gold will displace the iron behind the riffles, as long as there is movement there.

 

 

By Dave McCracken

The water flow should be just enough to keep the concentrating action going behind each riffle, yet not so much that the riffles are being swept clean.

Dave McCracken

 

As a general rule, the optimum slope-setting of a sluice is around one inch of drop per linear foot of box. This can change, depending upon the volume and velocity of water being used, and/or the average shape, size, volume or weight (specific gravity) of material that you are processing.

There is no exact formula for setting the proper water velocity through a sluice box which will work optimally under all conditions for all the different types of riffles being used today. Therefore, rather than give you a formula, I will attempt to give you an understanding of what affects the proper amount of water velocity will cause in a sluice box, and also what the affects are of too much or too little water velocity. In this way, you will be able to act from direct observation to ensure that your, or anyone else’s, sluicing device will be recovering gold to the fullest extent possible.

In setting up a sluice, if feasible, it is desirable to have enough water flow to move the material through the box as fast as you can shovel (or dredge) it in at full production speed.

Most of the riffles being used today are designed so that a concentrating-action takes place behind the riffles. By increasing or decreasing the amount of water velocity over a set of riffles, the amount of water-action behind each riffle is also increased or decreased—which has an effect on the amount of concentrating action taking place. Water velocity can be increased by either putting more water through the sluice box or by moving the same amount through faster. Optimally, the water flow is just enough to keep the concentrating action going behind each riffle, yet not so much that the riffles are being swept clean (called “boiling”) of their concentrated material.

How much water velocity is directed over the box directly affects how much material will stay behind the riffles. When the correct amount of water force is being put through a sluice, its riffles will run about half full of material, and the material can be seen to be dancing and vibrating behind the riffles (concentrating) when the water is flowing.

If too little flow of water is directed through a sluice box, not enough water force can get into the riffles and they will “pack up” with material. In this case, little or no concentrating-action will take place and gold recovery will be poor. When this happens, little or no visible vibrating action behind the riffles will be seen and material will not be moving through the box fast enough to allow you to feed the sluice at production speed without loading up the entire box.

Too much force of water through a sluice box will put too much turbulence behind the riffles. This will cause some of the heavier concentrated material to be swept out of the box.

When this happens, gold recovery will also likely suffer, because the areas located behind the riffles are not calm enough to allow some percentage of the finer pieces of gold to settle. You will notice in this case that the dancing action is occurring behind each riffle, but less material will collect behind the riffles because of the increased amount of turbulence there. When you have too much water velocity, as material is shoveled into the box, it passes through very quickly and has little time to make contact with the riffles.

All the above points remain true when adjusting to get the proper amount of water flowing over an expanded metal-riffle system. However, when using such a system, it is necessary to remember that the riffles are very short. So it does not take very much water velocity to make them concentrate properly.

This means that the size of riffles affect how much water velocity is optimum through the box, how much classification of material is necessary and how fine in size your effective gold recovery will be.

The correct amount of flow is usually found to be just enough to move the material over the box to keep up with your feed of material. Since gold is around 6 times heavier than the average material that will pass through a sluice, there is usually some margin for error if velocity is a little faster than necessary. But a faster flow (than necessary) will affect how fine in size your effective gold recovery will be, if fine gold is present.

Once you have your sluice box set up the way you think it ought to be, it is a good idea to run a sizable portion of gold-bearing material through the box and then pan some samples of the tailings. If you do not find any gold in the tailings, you are set up properly. If you are finding gold in the tailings, some changes are in order. Another test is to mix some pieces of lead in with some material, run it through the sluice, and see where the lead stops.

Sluice boxes process material best when receiving it from a steady feed. Too much material dumped at once into a sluice box has a tendency to overload the riffles and choke off the concentrating-action behind the riffles. This will cause gold to wash right through the sluice box as if there were no riffles present at all.

On the other hand, it is not good practice to run volume-amounts of water flow over a sluice box without some material being constantly or regularly fed through. This is because the scouring-action from the water flows will continue to further-concentrate materials trapped behind the riffles, causing heavier materials to be washed out of the box. A sluice box operated for extended periods with no new material being fed to it has an increased chance of losing some of its fine gold values. How much gold loss will depend on a multitude of factors, such as the type of riffle design, how much water flow, the type and weight of concentrates and the size and purity (specific gravity) of the gold.

So if you will not feed more material into your sluice for a while, it is a good idea to cut your water flow back to reduce turbulence behind the riffles until you are ready to feed again.

Even when a sluice box is set properly, occasional larger-sized stones or rocks can become lodged within the riffles. These should be picked or flipped out of the riffles with minimum disturbance to the remaining portion of the sluice.

On most suction dredges, the volume of water being moved through the sluice continues at the same steady flow during production speed. So adjusting the water velocity to set up the dredge right is accomplished by changing the slope of the sluice box itself—which will speed up or slow down the flow of water over the box. Then, once you are dredging, if you will stop feeding streambed material into the suction nozzle for any period of time, it is wise to block the nozzle with a larger-sized cobble to slow the water flow through your sluice box.

When placing a sluice box within a stream or creek for its water flow, the water velocity can be adjusted by either changing the slope of the box, by varying the volume of water being directed through the box, or by placing the sluice at different sites in the stream or creek where the water is moving at different depths and speeds. Getting the right flow of water to pass through a sluice box out in the field is not difficult. But it is sometimes necessary to try different ideas until you find what works best in each situation. For example, in a location where the water is moving slowly, you might be able to direct more water through the sluice and gain the amount of water velocity that you need. In a stream where the flow is moving more swiftly, the water velocity through your box can usually be adjusted by changing the volume of water directed into it, and/or by varying its downward slope.

Usually, you will have little trouble arriving at the correct velocity through your sluice box when placing it in a fast stream of water. You can use river rocks to make a foundation within the stream so your box can sit level from side to side. By allowing different amounts of water volume through the box, and by changing its downward slope, you can work out a combination that does the job. It is good to have a length of nylon cord along with you for securing the sluice box to a rock or some other object upstream. This prevents the box from being moved off its foundation by the force of water. Sometimes it is necessary to pile a rock or two on top of the box to hold it in place. This is especially true when you are using a sluice made out of wood. You can shovel gravel into the box while trying the different combinations to see what effects the changes have on water velocity.

In a situation where you must set your sluice into slower water, you will find it is generally more difficult to get the flow you need, because you have to create more water velocity than is presently there.

If the flow of the stream itself is not enough to move material through your box, you will sometimes find that changing the slope of the box within the stream has little or no effect on speeding up the flow through the sluice. In this situation, there are several things that might be done to channel enough flow through your box so that you can run material through at production speed. Sometimes the flow of water within the overall stream itself is enough, so that by setting up a “water director” in the stream, you can move enough water through the box to give you the desired result. A water deflector, or barrier, like this can sometimes be built by throwing river rocks out into the stream to make more water flow into and through the sluice.

In this situation, there are several things that might be done to channel enough flow through your box so that you can run material through at production speed. Sometimes the flow of water within the overall stream itself is enough, so that by setting up a “water director” in the stream, you can move enough water through the box to give you the desired result. A water deflector, or barrier, like this can sometimes be built by throwing river rocks out into the stream to make more water flow into and through the sluice.

Sometimes you can get the water velocity needed by arranging a small water-elevator across the waterway. By doing so, and by placing your sluice where the moving water spills over the top, you might create more than enough water flow through the box to meet your needs. It really does not take very much volume of water through a medium-sized sluice box to get the right amount of velocity, if the water is moved through the box at speed. In the case of a short elevator (dam), the water level might only need to be raised up slightly to increase the downward slope of the box enough to create the needed water velocity. How high the elevator needs to be depends mostly upon how much water is flowing within the stream or creek.

A sheet or two of thin plastic, or a plastic tarp, or some old rice bags, can come in handy when you are arranging an elevator or water director within a stream. Such material helps prevent the water from pouring through the holes in your man-made barriers.

A water director or elevator can most often be used with good result wherever the water in a stream or creek is moving and is shallow enough that the barriers can be built easily.

If the water at the work site is moving too slowly, or for some reason a water director or elevator will not work in a particular location, it will be necessary to either set up your sluice in a different location where the water is moving faster, or use a motorized pump to feed water into your sluice. Or, in some situations, it is possible to siphon water into your box from a higher point upstream. Siphoning can be done effectively with the use of reinforced garden hose(es), other types of heavy-walled water hose or PVC.

 

 
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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 Ron Wendt

“I Remember Seeing The Miners Coming In With Bags Full Of Gold…”

 

Sluicing in AlaskaThe old man leaned against his shovel and wiped his brow as the hot interior Alaska sun beat down upon him. He was a veteran of the gold rush. He had missed too many boats and never quite made it back out of Alaska. It had been over sixty years since he had walked the streets of Seattle, where he first caught a boat to head north to the Klondike. It was the gold that kept him here, and his sluice box, shovel, and gold pan were an integral part of him.

He looked at me and never said a word. Even at my age in the early 1960’s, I could tell he was not having any fun. It was a tedious job for him. He shafted to bedrock during the winter and sluiced in the summer. As my father used to tell me, “He made enough gold to buy beans.” The old man was content with his life in the wilderness where he answered to no one; only the occasional camp robber or raven would land nearby, begging for a few scraps of food the miner had.

Even in the late 50’s, as a small boy, I remember seeing the miners coming in from the Fortymile River with bags of gold, begging for someone to buy it just so they could feed themselves. One miner had a cake pan full of nuggets he tried to peddle. He wanted $500 for the whole pan, but my father could only afford to buy a few choice nuggets from him at a cheap price.

Sluicing 2My first homemade sluice box was built from old photos, some advice (some poor and some good), a few aged pieces of plywood and two-by-fours, wooden slats for riffles and burlap to catch the gold. At sixteen, I had visions of gold, just like any other person would after reading Jack London’s books and other stories about the gold rush. Having been raised in the gold camps of the Circle Mining district in eastern Alaska, I had watched many miners, including my father, extract gold with sluices and gold pans.

Here I was in the Yentna River area near the Alaska Range, with a water-logged wooden sluice box, trying to make my first big strike. Believe me, there is nothing worse than trying to move around water-soaked wood! With the help of a more seasoned prospector, we located a bench of pay-dirt where a false bedrock of clay rose up out of Twin Creek. Through some trial and error, I figured out that the gold was in the clay. After shoveling tons of dirt and clay into my sluice, I soon discovered that I was not breaking up the clay enough and was losing quite a lot of gold with the tailings.

Between shoveling into the head, and raking rocks through the sluice, just as I watched that old man do years before, I was able to recover six ounces of gold for the two mosquito-infested, rain-soaked months that I worked this bench. Though it wasn’t a fortune, I didn’t care; I felt as happy as that old-timer probably did when he just got started years before. I have learned a lot since then, but I still value all of the early golden lessons taught to me by those old sourdoughs.

Eventually, I graduated to the wonderful world of aluminum. The aluminum sluice has been a great blessing to the modern day prospector. They are great for back-packing and throwing around in the back of the pickup. They don’t break; and if you learn to master them, they will reward you with great recovery results.

Some places in Alaska are pretty remote. Not always can one put a suction dredge in just anywhere. It is so much easier to walk into the hills with a four-foot, fifteen-pound sluice box, than hauling a 200-pound suction dredge over hummocks and through alders. Each piece of equipment has its place.

I have always recommended that if you are going to get into prospecting, start out small. Start with a gold pan, then sluice with pick & shovel, then eventually get into a dredge system. From there, who knows–maybe a D-8 will be your next tool!

I have found that if you are going for the gold, like most everything, unless you are pretty lucky, you will not strike it rich right off. Finding the high-grade gold deposits is something that gradually happens as you learn the right approach.

I have also found out that when new prospectors start off all gung-ho into this business, hauling in big equipment where there is not much gold, they usually lose interest real fast. After two or three outings, a few thousand dollars of investment and no return, they get discouraged and quit.

I suggest it is better to start small and learn the art of prospecting. Shoveling into portable sluice is an excellent, economical way to learn the basics of finding gold.

In the old days, the sluice boxes were usually 12-to-14 inches wide, pieced together in telescoping sections, with pole riffles. The boxes were set at an average grade of six inches to the twelve-foot box. Water was directed to the head of the sluice from a long flume or a canvas hose coming from a dam. As in today’s sluicing operations, the name of the game was production, shoveling the most pay-dirt into the sluice. With long lines of sluice boxes, the kind you see in the old photographs, miners would try to set up the sluices so there would be six feet open on either side of the boxes. The lighter material was shoveled in while the larger rocks were placed on bedrock and washed later on.

During those days, shoveling-duty varied with the nature of the gravel and bedrock, how far pay-dirt had to be lifted to the sluice from the excavation, and the person’s capability to work. Under ideal sluicing conditions, a shoveler could feed as much as 2 ½-to-10 cubic yards of gravel in 10 hours.

In 1905 on Anvil Creek near Nome, there was one elaborate set of sluice boxes set up on bedrock. Five strings of sluices were shoveled into 24 hours a day by 120 shovelers. They were able to process an average of 1,080 cubic yards of pay-dirt per day during this time.

The good thing about prospecting with a sluice box is that you can process a lot of material just using a good No.2 shovel and a sharp pick. A sluice is an excellent way to scout out good future prospects.

I have heard some pretty interesting stories about sluice boxes. One classic story I remember happened up on the Koyokuk River around 1914. A prospector made a big strike; but all he had was a gold pan, shovel and an ax. So he cut down a tree, split-out a four-foot piece, carving out a set of riffles along the bottom edge. Although this was indeed very crude, the prospector found enough gold in two days to party in San Francisco for four months!

When sluicing with a portable aluminum sluice, there are several key factors to be aware of:

1. Water-speed is critical to gold recovery. Some gold can be lost out the end if the water is too swift-flowing through the box. If the water-flow is too slow, the heavy rocks, black sand and/or garnets can clog the riffles and the gold can wash out. So it is critical to learn water-flow. In my own experience, water-flow in the sluice should be no more than three inches deep with a flow that will tumble golf ball-sized rocks out the end.

2. It is important to keep the sluice box raked out after one or two shovelfuls of pay-dirt are fed into the head of the box. Allowing too much material to pile up in the sluice can also cause erratic water flow in the sluice. This can cause a gold loss, too.

3. The sluice should be on a slight slope. Most streams have a natural slope as they flow along. But there are times when the sluice needs to be adjusted to increase water-flow, especially in wider, deeper water. Sometimes, water-flow can be increased through your sluice simply by raising up the head of the sluice; and, whenever needed, using rocks underneath and around the sluice to dirvert more water.

For under $200, a prospector can be outfitted with an aluminum sluice, gold pan, pick and shovel. The sluice is one of the handiest prospecting tools next to the gold pan.

 
 
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This story first appeared in Gold & Treasure Hunter Magazine May/Jun, 1992 on Page 36.
This issue is still available! Click here.

By Dave McCracken

Experienced gold miner lays out fundamentals of running a successful surface prospecting program.

 

A “sluice box” is a trough-like gold recovering device which has a series of obstructions or baffles, called “riffles”, along its bottom edge. While a steady stream of water is directed to pass through, streambed material is shoveled into the upper-end of the box. The flow of water washes the streambed materials through the sluice and over the riffles, which trap the gold out of the material.

The reason a sluice box works is that gold is extremely heavy and will work its way quickly down to the bottom of the materials being washed through the box. The gold then drops behind the riffles and remains there, because there is not enough water force behind the riffles to sweep the gold out into the main force of water again.

A sluicing operation, when set up properly, can process the gold out of streambed material about as fast as it can be shoveled into the box. This can be many times more material than a panning operation can handle, yet with similar efficiency in gold recovery. How much material can be shoveled into a sluice box greatly depends upon the consistency and hardness of the material within the streambed itself, and how easily it can be broken away.

A sluice requires a steady flow of water through the box to operate at its best efficiency. Most often, the box is placed in a stream or creek where water is moving rather swiftly, with the sluice being placed in such a way that a stream of water is directed through the box.

In locations where water is available, but is not moving fast enough to be channeled through the box for sluicing purposes, the water can be pumped or siphoned to the box with excellent results (covered later). How much water is available, and whether or not it will need to be transported to your sluice box, is something that needs to be considered during the planning stages of a sluicing operation.

Because so much more material can be processed with a sluice, than with a gold pan, streambed materials which contain far less gold values can be mined while recovering just as much or more gold. Therefore, if the streambed material had to pay a certain amount in gold values in to be worked with a gold pan to your satisfaction, gravel containing only a fraction of as many values can be worked with the same result using a sluice box. This is an important factor to grasp; because it means the modern sluice box opens up a tremendous amount of ground that can be profitably mined by an individual.

Motorized sluicing (also often called “high-banking”) is an activity similar to sluicing, except that sluicing is almost always accomplished with the water-flow from the creek or river keeping gravel moving through and over the riffles. As demonstrated in the following video sequence, a motorized sluice (also called a “hydraulic concentrator”) is usually set up with a water pump that supplies water for the sluice box:

Motorized sluices are usually equipped with a recovery system that is set up with adjustable-length legs. This allows the box to be adjusted from side to side and front to back on uneven ground. This allows the water flow to be created for optimum gold recovery. Most motorized sluices available on today’s market also include a screening device over the top of the feed-section of the sluice box. Screening the larger-sized rocks out of material to be sluiced is one of the primary methods for improving fine (small) gold recovery. Any time you can screen larger rocks out, you can slow the water down through the sluice, which will allow even smaller particles of gold to become trapped inside the riffles.

In normal sluicing, the operators must find a location alongside of a creek or river where the water is flowing just right, at the proper depth, to set up the sluice so the proper amount of water can be directed through. Once the sluice is set up, gold-bearing material must be carried to the sluice, screened separately, and carefully fed through the sluice box.

With a motorized sluice, all you need is a supply of water within several hundred feet of where you want to dig. The screen and sluice assembly can be set up directly at the work site so that pay-dirt can be shoveled directly onto the screening section. The pump/engine assembly will pump water from the water source, through a pressure hose, to the sluice.

Another advantage to the motorized sluice is that in some areas today, it is not legal to wash silt directly from the bank into an active waterway. With a motorized sluice set up some distance from the stream or river, you have an opportunity to utilize natural contours up on the land to slow the water down enough to allow the sediments to settle before (if ever) the water re-enters the creek or river.

SAMPLING

Just like in any other type of gold mining activity, the key to doing well is in digging sample holes to first find a high-grade gold deposit.

Placer Geology

In many places, there is more gold up on the banks than you will find in the river. This can sometimes be true on the Klamath River in northern California. Actually, it is not only that there is more gold on the banks than in the river. The gold on the banks can sometimes just be easier to get at for a small operation.

What happened along the Klamath River, and in many other areas, is not difficult to understand. The old-timers started mining down in the creek or river, and moved uphill, allowing gravity to carry the water and tailings back down towards the creek or river. As the old-timers worked further up into the banks, often the gravel became deeper and more difficult to remove by conventional hand methods. In time, the old-timers developed hydraulic mining. This is where they directed large volumes of water from nearby (or sometimes distant) creeks under great pressure through monitors (huge pressure nozzles). The high-pressure water was used to wash large volumes of gravel through large sluice boxes placed on the banks of the creeks and rivers. As the sluicing operations cut further up into the banks, the sluice boxes were moved forward, which left tailings deposited on the banks.

It is estimated that as much as 50-percent of the gold washed right through the sluice boxes in hydraulic operations because of the large volume and velocity of water which such operations used. Hydraulic operations did not lose gold in the same amounts all of the time. Much of the gravel that these operations processed contained little or no gold. The concentrations of gold were found along bedrock or at the bottom of lower strata flood layers. So, valueless top-gravels were processed at volume speed, and they would try to slow down when getting into pay-dirt materials. Sometimes, however, they would cut into pay-dirt materials at volume speed–before having a chance to slow down. This is where large volumes of gold would wash directly into the tailing piles.

Since the time of large-scale hydraulic mining, there have been several occasions of extreme high water. The 1964 flood in the western United States is one example. Floods of such magnitude, all throughout gold country, re-deposited old hydraulic tailings piles into newly-formed streambeds up on the banks and within the active waterways. Places where gold was lost from hydraulic operations formed into new pay-streaks–often only inches or a few feet from the surface. This is true all up and down the banks of the Klamath River–and probably many other rivers as well–which has created a wonderful and exciting opportunity for modern small-scale gold miners.

Contrary to popular belief, many pay-streaks today are not found down along the bedrock. In fact, many of the pay-streaks surface miners are finding along the Klamath River are situated in a flood layer (1964 flood) within two feet of the surface. This flood layer is often resting directly on top of undisturbed hydraulic tailings.

We are also finding similar pay-streak deposits inside the active river with the use of suction dredges.

Finding pay-streaks with a surface digging project is usually done by setting up the sluice in several different locations, and giving each sample a large enough test hole to obtain an idea of how much gold the gravel is carrying. Sample holes should be taken to bedrock if possible. However, if the gravel goes deep, you have to avoid getting in too far “over your head.” At the point where you start digging deeper than 3 or 4 feet with a pick and shovel, any pay-streak is going to have to be exceptionally rich to make the effort worthwhile. Richer deposits are more scarce; and therefore more difficult to find. So it is important to stay within effective digging/sampling range, and not get yourself into a full-scale production operation before you have found a high-grade gold deposit.

Sometimes you can learn valuable information before you start sampling. If other miners in the immediate area are finding gold deposits along a specific flood layer, you should be sampling for gold along the same flood layer while digging around in the nearby vicinity. Gathering information such as this is one of the many benefits of belonging to an active mining club or association. Active mining organizations will include others who are actively pursuing the same type of mining activity that you are engaged in.

While sampling with a pick and shovel, it is very seldom that you will actually see gold in the gravel as it is being uncovered. Usually, you do

not see the gold until it is time to clean-upthe sluice box after the sample is complete.

If you finish a sample hole and end up with a good showing of gold, the next step is to find out exactly where the gold came from. In other words, did it come off the bedrock, or did it come from a particular layer in the streambed? You must know where the gold is coming from to evaluate the value of the pay-streak. For example, digging two feet into a paying flood layer requires much less time and effort than digging four feet and having to clean rough bedrock. If you do not know for certain where the gold is coming from, and you assume it is coming from the bedrock underneath four feet of hard-packed streambed, you might decide it is not rich enough to work and walk away from a very rich deposit located at the two-foot flood layer

At the same time, if you are able to reach bedrock, you always want to get a good sample there by thoroughly cleaning the surface and any irregularities there. Sometimes that is where the richest deposits are found.

Pinpointing the source of gold is reasonably easy once the sample hole has been opened up. It is likely that the gold will be concentrated either along the bedrock, along the bottom of a flood layer, or at both locations. Sometimes, there is more than one flood layer that carries gold. You can run small production samples of each stratum separately to see which is paying. Or, sometimes you can simply take pan-samples in the different contact zones between the layers

Some pick & shovel miners are using metal detectors in their prospecting activities. Some of the new gold metal detectors will sound out on pieces of gold as small as the head of a pin! But in gravel deposits, metal detectors can also be used quite well to locate the concentrations of magnetic black sand. Black sand tends to concentrate in pay-streaks, just like gold. Therefore, locations sounding out heavy concentrations of magnetic sand on metal detectors are excellent places to follow up with pick & shovel sampling.

One question commonly asked about sluicing procedure is the proper slope-setting for a sluice box. A sluice box generally requires about an inch drop per each linear foot of sluice. This is just a guideline. Basically, you need enough water velocity to keep the material active in the sluice behind the riffles, but not so much that you are washing most of the material out from behind the riffles. I like to get enough water flow to keep the larger material moving through and out of the box. If I see lots of rocks building up in the sluice, I know I do not have enough water velocity. An occasional rock needing to be helped along is alright in a sluice (although maybe not a dredge sluice!). In surface sluicing (non-dredging), I would rather toss out an occasional rock and have the peace of mind that I am also achieving maximum possible fine gold recovery.

A common practice in sluicing is to also to set up a second sluice behind the primary sluice. The plastic Le’Trap sluice works exceptionally well for this because it recovers fine gold so well, and for its ease in cleanup. The idea is to have a safety check on your primary recovery system to make sure it is working properly.

And if all else fails, you can always do some pan-testing in your tailings to see if your sluice might be losing any gold.

One mistake that beginners often make is in thinking that the recovery system is at fault because they are not recovering very much gold. Most often, however, it is not the recovery system. It is the lack of a good-paying pay-streak! The answer to this is to hustle around with more sampling. Ask around to see what and where it is working well for others in the area. Use their operations as a model.

Flood layer pay-streaks are often easier than bedrock pay-streaks to clean up with pick & shovel surface mining operations. There are several reasons for this. One is that a flood layer pay-streak is closer to the surface. This means less gravel to shovel to reach the gold. Another reason is that it takes more effort to clean the gold off of a bedrock surface when you are not using a dredge. You can only do so much with a shovel. After that, you must resort to a whisk broom and/or a motorized vacuum cleaner. This is why portable dry land dredges are also becoming so popular. They give you the ability to clean bedrock surfaces and cracks with minimum effort. If the gold is coming off bedrock, you must invest the extra effort to clean it off well. Otherwise, you stand the chance of leaving an important portion of the gold behind as you mine forward on the pay-streak.

Many pick & shovel miners today also are equipped with an optional suction attachment. To use it, the pressure hose from the water pump is attached to a suction nozzle that directs the water and material through a suction hose into the sluice. So after an initial hole is dug up out of the water, the hole can be filled with water and material can be sucked into the sluice box. The recovery system can be positioned so that the water discharge can run back into the hole– keeping the hole from running out of water.

So you can dig a hole up on the land, and then begin a suction mining operation outside of the active waterway. This is great!

In California, dredging permits are only required when dredges are operated inside of the active waterway. Therefore, my personal understanding is that suction miners up on the land are not required to have a dredging permit as long as they are not dredging inside the active waterway.

Some surface miners also sample for the gold-path up on the bank by pan sampling the moss. Sometimes, how well the moss is producing gold at the surface can also be an indication of how well the gravel is paying underneath.

When moss, roots, clay and other types of materials are producing good quantities of gold, it is always a good idea to break up the material as much as you can before running it through a sluice box. This is usually done by pulling it apart over the top of a classification screen, or breaking it up inside a bucket of water before running it through the sluice. This slows down production, so the additional work must be rewarded by the recovery of more gold.

Once you find a pay-streak in pick & shovel mining, you want to give some thought to how you are going to develop the deposit with a minimum of wasted effort. For example, you will have to pile the cobbles (rocks too large to pass through your recovery system) and tailings somewhere. Preferably, cobbles and tailings would not be placed upon some other section of the pay-streak. Otherwise they might need to be moved twice, or you might be forced to leave behind high-grade areas that have been further buried. So it is worth some extra sampling to get an idea of the pay-streak’s boundaries. Then you can deposit the tailings material in a location where you will not need to move them again.

Placing tailings is, and always has been, one of the most important aspects of a mining operation–of any size. Yet, it is one of the most neglected aspects of mining by a substantial portion of small-scale miners. In fact, we have a standing principle, true as it may be, along the Klamath River: “Dowsing works: just look where a successful pick & shovel miner or dredger has been throwing his or her cobbles. It is almost guaranteed there will be excellent gold underneath!”

This usually comes back to a simple case of gold fever. The miner starts getting a good showing of gold, gets excited, and never slows down to define the boundaries of the deposit. This almost guarantees an important portion of the deposit will end up underneath cobbles.

Pay-streaks up out of the water are often different from those found in the river or creek. What I mean by this is that they do not always follow the same gold path. When you find a pay-streak in the river, you can usually line it up with the next river bend and make a pretty fair guess where the next several pay-streaks are likely to be. This is because river pay-streaks usually form from gold that has washed down the river along its own gold path during major flood storms.

Pay-streaks outside of the river often were formed from gold out of tailings from old hydraulic mining operations. So you can find a small pay-streak up on the bank, follow it until it plays out, and then not find any sign of it further upstream. This is because the source of the gold deposit was not from a point further up river. Then you can find another pay-streak on another path altogether. In other words, pay-streaks up on the bank might not follow a specific single gold path, as they usually do in the river.

Pick & shovel mining is a lot of fun – when you are finding gold. A healthy portion of our miners along the Klamath River mine out of the water. The reason for this is that it gives them an opportunity to find pay-streaks without having to commit to an underwater dredging operation.

We manage Group Mining Projects just about every other weekend during the spring, summer and fall months in Happy Camp You can find this year’s schedule HERE. You have my personal invitation to come out and get some firsthand experience. We always send participants home with a sample of gold that they help recover–that is, those who go back home. Many join up with us. Watch out–the biggest challenge in gold mining is not in finding the gold; it is getting over the “fever” after you have found it!