Cracks
As long as water flow velocity is high enough to move the gold, the gold will continue to move. We’ve talked about curves and their effect on water pressure, and we’ve also talked about objects that water must flow around, like boulders. We’ve also talked about the fact that gold crawls along the bottom of the river as bed load. It will continue crawling along the bed as long as the water velocity is sufficiently high enough to move it. Two conditions can present themselves to stop the gold from moving down the riverbed; 1). the river bed can be rough, jagged, and craggy where gold will “hide” from the high velocity currents, and 2). the river bedrock will have cracks and crevices into which the gold will drop. Once the gold has found one of these locations, it will remain their until either the bedrock is broken up by water action, earthquakes, or the pounding of large boulders as they are moved down river.
Smooth bedrock give the gold no place to hide from the forces of the water pressure, and so it will continue down river until it does find a hiding place.
So, if you dredge in a location and reach bedrock, but the bedrock is smooth, move to another location. It’s always possible you may find the occasional nugget, but more than likely, your wasting your time. If, however, the smooth bedrock has cracks and crevices for gold to drop into, work them.
A crack in the bedrock does not have to be large. Wafer thin pieces of gold will work their way down into even the smallest cracks. It is well worth your will to open these cracks and clean them out. In fact, clean them out two or three times. Use both the high pressure water jet tapped off the water pump and crevice cleaning tools.
Cracks that look very thin can also open up farther down making a large pocket in which gold can accumulate. An amazing amount of gold can come out of a crack that doesn’t look like it could hold any. Do Not pass up any cracks or crevices in the bedrock.
Channels
Gold moves when water flow velocity is high enough to overcome the weight of the gold. When the water velocity decreases, gold stops moving. It can hide behind an object that has interrupted the flow of water, or it can fall into a crack or crevice and hide from the water’s force. It can also stop when water slows down as it flows around the inside of a curve. A fourth place is where the river widens into an area of slow moving water (commonly called a pool).
Let’s consider a specific quantity of water. When that water moves through a area that is 25 feet wide, it moves at a certain speed. If that same quantity of water moves through an area that is 100 feet wide, it slows down. Just like what happens when a river flows into a lake.
When the gold is pushed through a narrow stretch in the river, it moves at a certain speed. When it enters a pool the water slows down and the gold drops. So, there will be an area at the beginning of the pool that may have a good gold concentration. If present, it will probably be evenly distributed across the width of the pool, so look for places where the gold will pocket (exposed bedrock, boulders, cracks, crevices, etc).
The above discussion will give the novice prospector a good idea of how to read a river to find where gold will “pocket.” Of course, you can follow each of these lessons in detail and still not find a lot of gold. First, make sure you are looking at a river that is known to contain gold. The old timers didn’t get it all, but if a river has some, they probably found it. So, don’t waste your time looking in a river that has never had gold in it.
Practice reading rivers to see where you might want to dredge, even if not right now. As with any skill, reading a river and finding gold takes practice. Talk to those who know the river. They can save you a lot of time.
More tips on Dredging Gold:
Tip #1
Do not run a dredge motor without an air filter. Even though it may not look dirty, microscopic dust will score the intake valve and the combustion chamber, greatly reducing the life of the engine. Change the air filter a minimum of once per year.
Tip # 2
Change the engine oil after the first 5 hours on a new motor. This is “break-in oil.” After that, change the oil every 20-25 hours running time. Typical dredge motors do not have an oil filter, and the oil must be changed more often than your car. Use ONLY grades and weights of oil recommended by the manufacturer. For Briggs & Stratton engines, ONLY 30W detergent oil (not 10W-30 and not non-detergent oil).
Tip #3
Do not leave the dredge engine’s gas tank empty, even overnight. When done for the day, top off the tank with fuel to prevent condensation from forming in the tank.
Tip #4
To store the dredge engine at the end of season, hook a water supply to the pump (do not run dry). Fill the tank with fuel treated with a fuel stabilizer, such as STABIL. Run the engine for 5-10 minutes. Cover and store in an area not susceptible to gas fumes buildup.
Tip #5
When dredging, only run the engine as fast as necessary to provide good suction at the nozzle…not (necessarily) wide open. You want good suction to pull the solids all the way to the sluice box, but decreasing the speed of the water provides better separation of fine gold.
Tip #6
When operating the suction nozzle, don’t “jam” the nozzle into the gravels. Doing so will cause frequent plug-ups and overfeed the sluice box. The ratio of water to solids should be about 3:1 (3 parts water to 1 part solids), but no more than 2:1.
Tip #7
Don’t try to max out the size rocks that go up the suction nozzle. Even though you might have a 4″ nozzle, letting a 3 3/4″ rock to go up the hose will have a good chance of getting lodged and plugging up the hose at the joints. Instead, take the extra time to pull larger rocks out of the way.
Tip #7
Take a round file and taper the inside of the jet tubes. This little amount of tapering can help to prevent many plug ups.
Tip #8
Use ribbed carpet under miner’s moss in the sluice box. This will do a better job of catching fine gold than miner’s moss or ribbed carpet by themselves.
Tip #10
Keep a roll of duct tape (100 mph tape) handy. Good quality duct tape can seal holes in suction hoses, make temporary repairs to pontoons and other dredge parts, and serve a variety of other purposes.
Tip #11
Paint all tools bright florescent orange. Tools are much easier to see when they are bright orange instead of black. This is especially useful when working in murky water.
Tip #12
Take only the tools that are necessary for the job. In taking too many tools underwater, you run the risk of losing track of them. Tools can be easily covered with cobbles and debris.
Tip #13
Use a rubber “dead blow” hammer (2 1/2 lbs) to assist in unclogging the suction hose. The rubber head will not damage the hose and the “dead blow” design gives extra punch.
Tip #14
Repair holes in suction hoses as soon as possible. Gold “crawls” up the hose and can fall out of any holes in the hose.
Tip #15
Keep a bottle of isopropyl alcohol handy just in case gas or oil are spilled in the sluice box, cleanup tubs, classifiers, pans, or anything else used to process concentrates.
Tip #16
If you see an oil “sheen” anywhere in your concentrates, use one or two drops of dishwashing detergent to break up the oil.
Rio Suerte 