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Monday, November 16 2020
The use of water for grinding and milling has been in practice for thousands of years. From simple water wheels to inventors such as Archimedes of Ancient Greece and Bernoulli, a Swiss mathematician and physicist in the 1700s whose principles appear on modern day dredge nozzles, science has always advanced the use of water in our everyday lives. But have you considered just how much the dynamics of water can affect gold recovery?
Water Flow. The easiest example of how water dynamics affect gold is the classic inside bend in a waterway. When stream flow is straight and velocities are at their highest, gold will be suspended in the flow. As a bend in the stream causes flow to begin slowing down, the heaviest gold begins to drop out because the water no longer has enough velocity to suspend the material. The stream continues to lose power as the bend length increases and smaller and smaller gold continues to be deposited until there is no longer any in suspension, or the remaining water flow and speed cannot carry it farther downstream.
Water velocity and flow affect attempts at recovery in all capture devices in exactly the same way. Each piece of gold in classified material requires a certain flow and length of time to separate, drop out, and be captured based solely on its relative size and weight. If the velocity and flow are too great, the gold will remain suspended and will exit the machine regardless of machine length or method of recovery. This is why some miners are lured into a false sense of security just by using longer sluices.
Improper water depth in the sluice can create additional problems in recovery. Methods of material collection have much less effect if the gold is suspended in the upper part of the water flow. Most sluices provide little or no material agitation to break up the classified material and provide the necessary change in flow that facilitates gold separation. Lack of agitation allows smaller pieces to be carried through the equipment.
Classification. There is a direct relationship between material classification and water speed, which is often overlooked. It is common to classify for ease and speed of filling buckets rather than size of gold being targeted. Larger classification requires increased water speed to push the material through most recovery systems. The trade-off is forfeiting recovery of finer gold by increasing the length of drop time. This reduces the number of gold capture attempts and even machine effectiveness by having concentrations of larger material wedging into riffles, drops, etc.
Running dry material requires the sluice to liquefy the material while it is passing through. Gold particles will suspend in the dry material, reducing the chance of capture. Many miners use a scoop and drop their material into the machine in large clumps. This also allows particles to suspend instead of being processed. Material should always be wet prior to processing, and material should be cast (sprinkled) side to side across the machine when using a scoop.
Riffles. Some riffle designs are actually not that ideal for gold recovery. Some sluice riffles are evenly spaced, making them too far apart to impart the “vortex” or reverse underflow. What actually happens is an up-and-down wave motion as the water travels down the sluice. The only “action” imparted is the same negative flow that happens when water flows over a rock or some other obstacle in a stream. Material suspended at the bottom of the flow is deposited as the water climbs over the riffle and slows. Material that is heavy enough and can no longer be suspended drops. The rest of the material remains in the flow and continues to be carried down (and possibly out of) the sluice.
Flare. Most modern riffle sluices (standard and drop designs) are susceptible to improper setup angle, which can either clog the machine with material or blow it out completely. Either problem results in the loss of gold. Another big mistake in sluice design and operation is the “V” fallacy. The idea that channeling your water towards the center of the sluice using a wide-angle flare will increase its effectiveness and therefore increase gold recovery is false. On top of that, miners drop material into the center of the slick plate. This forces material into the center of the sluice, which is quickly overloaded by the volume of material and will cause the first series of riffles to lose their effectiveness.
Remove the flare from your sluice to eliminate the center concentration and create an even flow across the machine. You can create a V-shaped wing dam with a short straight section in front of your sluice if you need increased water flow or speed. Casting your material across the width of the sluice will eliminate overloading of the riffles.
Understanding how water height and speed changes your recovery can also make all the difference in boosting gold returns:
Water height. Begin with the water flowing just above the riffles or drops. Run small amounts of material and watch as the dirt passes through the sluice. Notice how the material enters the riffles or droops. Be sure to use the correct method of casting material evenly from side to side. Gradually increase the water height until processing suffers. This will determine the minimum and maximum water height for your sluice or highbanker.
Water velocity (speed). Set your sluice water height for max processing and a fairly fast flow, then gradually reduce water speed as you process small amounts of material. You may have to adjust your sluice to maintain proper water height through this process. Note how changes in water speed decrease the quality of material processing.
Spend some time exploring water dynamics. Introduce only one variable at a time, and verify how your gold recovery is affected before moving on. No doubt, with a little more understanding and experimentation, you’ll recover more gold with your sluice!
Monday, October 01 2018
A highbanker, sometimes called a power sluice, is a very flexible and efficient piece of equipment when you’re gold mining in areas with a good amount of water. Their main use is to allow you to pump the water to the gravels rather than carrying heavy buckets of gravel to the water. The optimal place to use a high banker is a location along a river where there are lots of bench gravels that have been left high and dry by erosion. Just shovel material directly into a high banker and let the equipment do the rest of the work! As long as there is sufficient water close by so the hose can reach it, you’ll be good to go. High bankers are available in various sizes. The bigger the unit, the more gravel it will handle in a day. That also means it will likely be heavier and less portable. High bankers are fairly simple to set up and operate. They have three main components: a hopper feed box, and sluice box, and a pump.
Hopper: The feed box contains a grizzly screen with a water spray bar. The water is normally sprayed from simple plastic pipes with a series of small holes drilled into them. A water valve located ahead of the spray pipe controls the amount of water flow going into the feed box sprays. A series of rods are arranged to make a slat-type screen (called a grizzly) that allows water and smaller material to fall through and go down into the sluice box. The large rocks that are caught by the grizzly are washed with the spray and then rejected. The slats should be set on an angle so that most of the larger gravel will slide off the slats by the pull of gravity without you needing to push them off by hand. Some rocks may hang up, but for the most part, they will slide off on their own. The spray water comes out under a lot of pressure and washes any loose sand or clay into the sluice and also provides part of the water needed to move material through the sluicebox area.
Sluice: High bankers utilize a normal sluice to recover the gold from the gravels, and the operation of the sluice box portion of a high banker is basically the same as that of a hand or stream sluice. With a highbanker, the water is supplied by a pump rather than the flowing water of a stream. The matting and miners moss underneath the sluice’s riffles are the same. Gold flakes get caught in the riffles and moss the very same way as it does in a hand sluice. A nice back-saving bonus on a high banker is that it will be on legs, so you can operate it on any terrain. A normal hand sluice lays on the bottom of a streambed.
Pump: The centrifugal type pump should be set near the water as it is more efficient to pump water uphill to the sluice than to suck it up to the pump. This is only important where there is a lot of vertical distance between the pump and the sluice. If there is less than 10 feet of vertical distance, it does not matter much. Pumps can be set up quite a distance away horizontally from the sluice. It will work so long as there is sufficient water at the source where the pump is located. Vertical distance is more of a problem than horizontal distance; 30-40 feet is the maximum vertical climb for most pumps. The standard lay flat type of hose is used to carry the water up to the feed hopper. Be sure to have enough hose and some extra in case you spring a leak! Remember to position the pump so that you aren’t breathing motor exhaust fumes all day!
The big advantage of a highbanker is working materials that are found in a location away from a river, like benches and other isolated patches of gravel. Moving the water to the sluice with a pump saves you from carrying the material down to the stream. The only disadvantage to highbanking for gold might be that it’s more equipment to pack around than just your usual digging equipment. It would be wise to test your ground before hauling in your high banker. Testing will indicate if there is enough gold in the gravels to warrant bringing in more than a hand sluice. If you have at least an amount of gravel that represents a full day of digging and sluicing, bring in a highbanker.
The adjustment of a high banker is much less than the steep slope you usually would use with a hand sluice. Adjust the water flow to the minimum flow rate that it takes to get all the rocks that fall through the screen to keep moving down the sluice box section. If rocks or gravel hang up and bury the sluice, you need more water and perhaps a steeper box angle to wash that stuff away. The height of the feed box is another important adjustment. You want it low to allow you an ease of feeding in the material. If too high, you will hurt your back lifting heavy shovels full of gravel. Too low and you may be constantly sweeping away tailings at the back of the sluice.
The feed box itself should be adjusted to ensure the angle of the slat screen rods (the grizzly) allow the gravel to be well washed before it moves out as waste. This is because a lot of small gold adheres too the larger cobbles. If rocks and cobbles just roll through without getting a thorough washing, you will be losing gold. The rejection of the large oversize rocks is important as it lets your sluice to a better job. If those bigger rocks make it into the sluice, you’ll be getting much worse recovery of fine gold.
Be sure the foot valve or strainer on the intake hose is clear and able to deliver a full water flow. Sometimes the foot valve can get clogged with leaves or other debris. A blocked or partially obstructed foot-valve won’t allow the high banker to operate properly. For environmental reasons, it is a good idea to have your water drain into a pond or pit that is not directly connected to the stream. This is so that the clay and mud can settle out, otherwise make sure there are no legal issues of putting that mud back into a flowing stream.
Some models of highbankers can also be run as a dredge. These highbanker/dredge combos can save you money, offer flexibility, but are also a bit of a compromise since the dredge portion is generally small. Combo units will be equipped with a suction nozzle type of intake. This design is best for working small shallow streams and tributaries. These systems are designed to be set up alongside the stream edge and have adjustable legs rather than float systems that you’d normally see on a larger suction dredge. With a suction nozzle and more hoses, the combo unit will operate as a suction dredge, picking up material from underwater crevices and delivering it to the sluice. Highbanker/dredge combos also can be ideal for working in and around ponds in old hydraulic mining pits.
The next time you are out in the field, consider if a highbanker or power sluice can help you get more gold. To determine if the answer is yes, ask yourself these questions: Where is the nearest water? Can I shovel directly from the diggings into the feed hopper? Can I set it up to allow gravity to do a lot of the tailings clearing work? Where will the pump go? With a little thought and planning, you’ll be able to decide if highbanking for gold will increase your productivity. In most cases it will. Move more dirt, get more gold! Good luck!
Monday, July 30 2018
Places where gold naturally concentrates in an environment of streams and drainages are known as paystreaks. No matter if you are panning, sluicing, dry washing, or metal detecting, in many ways your success at gold prospecting comes down to locating these elusive natural pay streak concentrations. Keep in mind that most gold paystreak formations occur during times of flooding and that many factors affect how gold gets deposited. Perhaps the biggest factor is that gold is dense and is more than 19 times heavier than water. The denser an object, the more easily it will resist the flow of moving water. That means it takes a very strong and fast moving water flow to move along a nugget the size of a pea.
When deciding where to start sampling, it’s helpful if you think of a river or stream as a sluice box. Waterways obviously don’t have aluminum riffles and matting, however, they do have natural gold traps that do the same thing that a sluice will do— allow gold to settle out of gravels and be caught while the bulk of the sands continue downstream. Heavy material such as gold doesn’t get spread along evenly, it is most likely caught in certain areas. The downstream parts of inside bends in a stream are favorable places to look for pay streaks. Just how good depends on how sharp the bend in the stream actually is. Usually the sharper the bend, the better the pay streak. If a tributary is known to have coarse gold, look at the intersection of the tributary and the main channel.
Behind an obstruction (large boulder, an island, or an outcrop of bedrock) is another good place to look for a pay streak. Boulders and other obstructions can create turbulence where ordinarily smooth flowing water turns into fast flowing whitewater. It is between the fast white water and the quiet dark water that gold drops out. The coarsest gold tends to be found on the outer parts of the pay streak, and the finer-sized gold is on the inner part of the pay streak. When you are working, if it seems as if the streak is petering out as you go toward the middle of the water flow because you are finding little gold, this region of the pay streak is often where the biggest number of nuggets are most likely to occur.
Once you know where paystreaks form, you might wonder if they are more likely found on bedrock or in gravels. They are nearly always found on bedrock or some sort of false bedrock. False bedrock might include caliche, a clay layer, or just a well-packed hard pan. You may just get lucky and hit something great with your first shovel of dirt, but more likely you’ll need to test a few different places. Even very experienced prospectors need to keep testing to find those hotspots and paystreaks. Good luck and keep sampling!
Wednesday, June 14 2017
Fun and exercise are two great reasons to go gold prospecting, but you might as well make some money while you're at it, right? The best way to do that is to increase production rates. Assuming you are mining on a known gold-bearing claim or waterway, volume is the key to your success!
Graduating from the basic gold pan to some other form of simple equipment is the best way to increase production rates. Just going from a pan to a sluice will increase production by at least 500%, depending on how it is used. A highbanker will work about the same amount of material as a well-run sluice, though it can move the water to you instead of you bringing the gravel to the water, thereby dramatically increasing volume of production. A drywasher will produce similar results by allowing you to work without water.
A dredge or highbanker/suction dredge combo is the next step up. A dredge uses a gas motor to generate the suction that will load and transport the material to the sluice, which greatly increases volume, as well as allows you to reach gravel on the river bottom that would otherwise be inaccessible (unless the river is seasonal or there is a prolonged drought). The more material a dredger can push across the riffles, the more gold can be recovered. An additional benefit to dredging is that it also allows you to clean gold out of all the cracks and crevices in the bedrock. A shovel just cannot do that.
The size of the dredge intake nozzle is the most important factor in how much material a dredge can process, but it is not a direct one-to-one relationship. For example, a 5 inch dredge will not move twice the material that a 2.5 inch dredge can move. It actually can move much more. The surface of the hose is figured in square inches, the area (and therefore the volume) goes up much faster than the diameter and the corresponding production rates go up proportionally. A larger hose size will also clog less because more sizes of rock and gravel will pass through. Having to stop and remove clogs can significantly reduce the time you get to spend actually moving dirt and finding gold. No matter the size, you're likely to have rocks jam up the hose from time to time, but generally, the larger the hose the less frequent the clogs that slow or stop production. In most areas of the country, a 2 inch dredge is considered a "recreational" size and may not require a permit to use, whereas much larger nozzle sizes would require a permit. Always know the laws where you intend to gold prospect and mine before you buy equipment.
Beyond dredges or highbanker/suction dredge combos, you can get into some professional mining set-ups that use trommels and jigs and shaker tables and earth moving equipment. Every deposit is different, varying in size and grade and structure. Environmental conditions and access will dictate mining methods and knowing the rock types and size of the gravel is critical in determining which equipment will work best for increasing your production. Finding a suitable deposit to mine and finding a way to work it economically— to justify your time and expense— is the first step. Then choose the right equipment to increase your recovery rate and speed of recovery and make more money. Good luck!
Saturday, July 02 2016
Although there are many variables that go into catching gold in a sluice, perhaps properly “tuning” your sluice is the most critical. A few months ago, Steven “Doc” Vetter, owner of Gold Hog brand mats, wrote an interesting article for Gold Prospector Magazine that focused on a few key factors that all miners should pay attention to. The following ideas from his article are all about achieving the proper tuning exchange, meaning letting the junk flow out, or be worked out by exchange zones, and holding the stuff you do want—gold. A well-tuned sluice will have heavy gold concentrations up top, medium gold in the middle, and trace gold near the end, and maybe a teeny tiny bit in the tailings. Here’s why:
Hydraulic Equivalence: By definition, “hydraulically equivalent” (HE) refers to particles of varying size, shape and density that fall out of a water flow and deposit in the same area. While quartz rock and gold vary greatly in specific density, you can make them collect in the same place by making the quartz rock bigger and rounder. A 2 inch quartz rock and a 1 mm sphere of gold will fall through water and deposit in about the same place— making them hydraulically equivalent (HE). An opposite example is a .25 inch round piece of gold and a .25 inch round piece of quartz. The gold will sink through the water and likely land straight down. The quartz rock, however, will not fall as fast and will be pushed several feet away before it settles. These two items are not HE.
The shape of the gold has a big influence on its HE. Flat things move more easily than spheres when either moving water or air is introduced. HE is a huge factor in gold mining and is often the main reason for classifying material to a certain size— the theory being if everything is about the same size, the heaviest material will stay in the sluice. When you slow down a sluice, you start to have a traffic jam. Things that are HE all want to gather in the same deposit zone and you start to gather/open the window for more non-gold particles to pile up and that’s not good.
Incremental Processing: A great analogy of how this principle works is to picture a city bus. Imagine a rule where all passengers must enter through the front and must exit through the back. As they enter, passengers must fill the seats in the front of the bus first. Every time the bus makes a stop (you shoveling dirt into the hopper of your highbanker or sluice), the first few rows fill up quickly and remain full for a short period of time. As a new passenger (each new shovel full of material) gets on and finds the front seats taken, he must move further down the bus (sluice). The result is a bunch of folks all competing for the same seats up front and when there are no seats up front, they must take the next available one. If all the seats get full, a passenger (your paydirt) never even gets to sit down and exits the bus (sluice) without ever sitting (collecting in the riffles). As the working zones in your sluice fill up, slurry material will move down to the next zone before it settles there. During times of heavy loading, the first percentage of your sluice will load up heavy and take some time to exchange out. That means gold will keep traveling until it finds an “empty seat.”
If you load too heavy or have too short of a sluice, you’ll have gold flowing over holding zones that are busy working and exchanging. It may take an exchange center (vortex) 3 or 5 seconds to fully process down material and exchange out non-gold and heavies.
Fine Tuning: Because of the principles of Hydraulic Equivalence and Incremental Processing, you may have realized that slowing down a sluice can really cause problems and loss of gold. How do you know if your sluice is running too fast or too slow? Experiment! Of course doing so is a little scary because the #1 fear of most gold miners is losing gold, and quite honestly, until your sluice is fine tuned, that just might happen. To avoid losing gold, most miners start running their sluice at the “normal” or widely accepted pitch of 1 inch per foot. But this is just a starting point. If you see gold in your tailings, your first thought is probably to slow it down so you aren’t blowing gold out of the sluice. But perhaps that’s not the cause at all. Perhaps it’s because gold doesn’t have a place to sink down into and hide in your sluice. Experiment by running way too fast, say at a 15-degree pitch. Then take it to 13 degrees, then go down to 12.5. Keep adjusting until you find an acceptable capture rate for the size of gold you want to hold.
Lose your fear of losing gold through testing and experimentation. Not only will you fine tune your sluice, but you’ll also get a great education. Good luck!
Saturday, March 01 2014
Some say that "gold is where you find it" and while that may be true, once you arrive at a known gold-bearing location, how do you decide where to dig first? Successful prospectors follow different methods, so there is no single "right" way, but no matter if you are sluicing, dry washing, or metal detecting, if you first consider the "lay of the land" you can better pinpoint a place to start.
Natural Factors to Consider Before Digging for Gold:
Man-Made Factors to Consider Before Digging for Gold:
Wednesday, May 02 2012
Place your sluicebox in the flow of a stream or river so that the water enters the flared end and flows through the sluice. If the current is strong you may need to lay some stones against the edge of the sluice to keep it from washing away. The sluice should be set at a downhill angle that allows the material to briskly flow through it. The higher the volume of water available, the shallower the angle will be.
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