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When you first walk up to a gold bearing river and try to picture where the majority of gold has accumulated on thing remains constant. Gold always follows the deep center channel until stopped by broken bedrock or simply the distance causes it to “settle out” (OK some finer gold does make it to the ocean). The point is, if you want quantities of our heavy yellow treasure it will be in the river’s main center channel usually under a lot of gravel and sand.
When the California gold miners of 1849 faced this problem they diverted entire rivers to reach the main center river channel. To be blunt – that’s where the lion’s share of gold is. That is, after you dig through all the sands and gravels to reach it. This river diversion method smacks of hydraulic mining that was done over 100 years ago now. It will wipe the majority of life from that section of river for many years to come. Thankfully there are different techniques to reach the gold that lies in the river center.
WAIT UNTIL LOW WATER
I guess that goes without saying but I felt I should mention it anyway. If the river you are going to mine is a rushing torrent I don’t think you are going to jump in and start working the main channel.
Safety is one reason we want low water flow, however, because of water’s “moving power” we need to have slow river water flow. I have used the following technique in select rivers with good success. Please be cautioned that this method can be dangerous so take every precaution.BEFORE STARTING:
- Is this river allowed to be dredged?
- Is there gold in this waterway?
- How large (wide / deep) is this section of river?
- How much over burden lies on the bedrock?
- Has this river been center dredged before?
The inspiration for this technique came from watching a river dredging company pump the sand out of a river side channel that boats used for transportation.
Although my thoughts for dredging were further upstream, I could see the speed and effectiveness of this method. They used a large centrifugal pump to directly pump a water sand mixture up onto the shore. I wondered how the pump could handle all that abrasive sand through the impeller fins. It was some years later that I found one of these pumps piled in a heap of heavy scrap metal. This location was in the back of an auto / truck grave yard. This thing was massive and probably weighed 400 pounds. I gave up on my truck parts quest and focused on unbolting the main side cover on the pump. Of course the 1 inch bolts were conveniently rusted into place but I found a piece of pipe about 12 feet long that fit into a socket bar and I slowly “snapped free” each of the 16 bolts on the cover. A lot of pounding later and the side cover sheared free. What I found inside was a badly worn impeller assembly that had so much play in it that I could move it up and down about 3 inches. The impeller fins were also “eaten away” so that they now resembled stubby paddles instead of the original full sized pump fins. It looked like the fins were made from cast iron or cast steel of some sort.
Anyway I am mentioning all of this to give you an idea of how this pump was built and all the wear that obviously took place when in direct contact with sandy water.
LOCATING A CAST IRON CENTRIFUGAL PUMP
A variety of industries have this type of pump, starting with:
- Water treatment plants.
- Large plumbing supply stores.
- Dredging companies.
- Scrap metal yards.
- Water heating companies (Hydronic).
- Boiler service businesses.
- Large ships, marine supply.
- Refrigeration (roof top water towers).
- Large truck service companies (Industrial machinery).
I am hoping you can pick up one of these as a used unit or scrap unit. The size of the pump is determined by the intake flange. A bare minimum of 3” intake is required but if you can get a 10” or 12”, take that.
The next trick is the engine to drive the pump. A 3” pump can be driven by a large 4 cycle motor (Honda or Briggs and Stratton; 6 – 12 hp). The exact horse power will be determined if you are stepping up the RPM or slightly reducing the speed required. Centrifugal pumps have a maximum RPM that the can run at. The bigger the pump the slower you have to spin them. This ranges from approximately 2,400 RPM for 3” pumps to 800 – 1,200 for 10” – 12” pumps. It will all depend on the internal fin design and what the manufacturer recommends for a maximum speed allowed.
You probably won`t have access to that information but if you can pull the name off the body of the pump and measure across the inside of the cast iron body you can do a Google search and probably locate some specs to help you. (Note: cast aluminum is not used for river dredging due to the excessive wear that will take place when in use).
A used centrifugal pump will almost always have worn out bearing at the shaft side. My advice is to simply use it as is unless the wear is excessive. I have drilled out old bronze bearings and replaced them but the trick is always to stay centered in the iron housing while you drill an oversized hole for the new bearing.
DREDGE PUMP SETUP
You will need a barge or twin hull deck to work from. Your pump placement should be centered, favoring the up current side of your floating deck. I always prefer to run my sluice boxes down the long running length of my barge. The weight of the water and gold bearing materials helps to stabilize my deck and I discharge the spent materials on the down current side (note: some areas don`t allow for this type of dredging so check local regulations). You will put a lot of silt back into the river`s flow as you work and the only other alternative is to pump the materials up onto the bank.
So my whole setup was:
- A twin hull 25’ long river barge approximately 15’wide.
- The Centrifugal pump was located towards the front of the barge with a flexible connecting pipe running to the aluminum down pipe.
- I chose a partly clear flexible suction pipe so I could see the volumes of gravels and sands passing through my system.
- I used a submerged classifier for better materials separation (front portion of the crash box).
- The classified gold bearing gravels were fed into three parallel sluice boxes (one for light flake gold, one for medium gold and the last for heavier coarse gold) that ran the length of my barge before emptying back into the river (the sluices were actually 18’ long).
- The flake gold sluice used a stepped dual riffle capture system which was cutting edge technology for the early 1980’s.
PUMP INLET SIZE
I generally restrict the size of materials to 1” minus on the intake side of the pump nozzle but it depends on what I am trying to achieve with the suction. If I am moving material to create a hole in the river bottom I will pre-screen to 2 – 3 inch. Now sucking this size of material through the pump is very hard on it and it will sound like your pump is breaking rock internally. I use this approach very sparingly – only when I am on a “hot spot” that I can’t vacuum down into the river bottom any further. By the way, this can jam or break the pump’s impeller fins (which is most inconvenient when you are 250 plus miles away from anywhere).
When you hit a “hot spot” (and you will) pay close attention to the size of gold you are trapping in your sluice box. Typically, in a good location, you should get up to 3/8” nuggets. This is where the highest current flow normally is and just behind large boulders on the bottom. You can feel these large rocks with your suction nozzle as you move it along. The other thing I watch for is the size of non-gold bearing material I am moving while working the good gold spots. Again you can feel what you are pumping (and excluding) with the suction nozzle. What has happened (more than once) is that I will pull some nice nuggets out of a high flow back eddy and suddenly it feels like I am hitting a concrete sidewalk. What has happened is as I have moved upstream following the coarse gold I will hit a heavy boulder area. The river’s current has washed away most of the smaller gravels and left some very large rocks in the faster current. Oh there is gold there but you are not going to suction the large rocks out of the way to reach those trapped nuggets. Either move ahead of this rocky area or keep working the smaller graveled section that you were working before you “hit the boulder area”. One last thing about rocky bottomed rivers, if you can dig a dip or hole in this rocky section make sure to work that area with the suction tube. The current may leave just the large rocks behind BUT there will always be gold in any depression or crevice.
DROP TUBE ON THE PUMPS INLET
Use aluminum for your drop tube into the river with a steel suction end. This type of suction tube cuts the weight you will have to move around considerably. The steel end can be made a variety of different ways. The most basic attachment is a domed ¼” thick steel tube shaped like a domed hat. This is the style I prefer for most general pumping. The shape prevents the end from being sucking onto the rock on the bottom but still allows for maximum recovered materials. If you are following my advice about the aluminum drop tube make sure it doesn’t have any bends in it. I am mainly talking about 45° and 90°angles. The pulled gold bearing material will rapidly wear these angled sections out. Another option is to Teflon line (using a Teflon insert) any bends in your suction tube to prevent wear.
HOW TO USE THE SUCTION TUBE
The whole point of this river dredge barge setup is to:
- Access inaccessible gold in the river’s center channel.
- Keep safe and out of the river’s main current flow.
The way I have used my river dredge setup is to tie off to one or both river banks. This is to secure your barge and prevent movement when you are dredging. Yes, an anchor can work but I find it hard to move small distances and still be able to retrieve the anchor when you are done.
Aim the front of your barge into the river’s current flow and drop your suction tube into the river at the front of the barge. The current will try to drag the tube under your barge so you may have to tie off the top of the suction tube onto the barge. If the current is moving too fast don’t try to dredge at that location. If you have to tie off your suction tube at the top there are several ways to accomplish this.
1) Using a cable or rope. This will work but restrict you for free movement of the suction tube. I have used a slip noose towards the top with some success but it is a pain!
2) Using a long steel pipe. This is my preferred approach as it allows me to vary the height of the suction tube without much problem. The steel pipe extends from the deck up to a big open ring at the top. The suction tube runs up through the ring, trapping it from being pulled under the barge from the pull of the current.
Typically I will clamp a large “T” to the down pipe 3 1/2’ to 4’ above the water level. This gives me the best leverage for “bouncing” the suction pipe across the bottom of the river. When you vacuum your way down deeper into the river bottom you will have to re-clamp the “T” handle. All the “T” is, is two half sections of the pipe with two feet of straight metal welded to it. I clamp across the half sections of pipe with bolts so that the handle is easy to move.MEDIUM SIZED RIVERS ARE BEST
This dredge will work in large rivers but I have found that medium sized rivers are the best choice here. If you do go after larger rivers focus your attention on the lee side of the outside bends preferring locations that have large rocks or boulders sitting at the front edge. Just behind this boulder “fence” there is usually an accumulation of fist sized rocks and gravel rich in gold. Of course it depends on the distance from the gold source and how deep the bedrock is.
Medium sized rivers offer maximum return for your labor. I will work these waterways in mid to late July right up until freeze up. Here we use every advantage with landslides or house sized boulders at or near the river center. All we do is use these restrictions to break the current flow on the barge and depending on the age of the landslide or massive boulders, suck out the concentrated gold bearing material that naturally sits behind them.
I will general vacuum out as much material as I can from behind these obstacles and then I will move back a minimum of six feet from the rocky restriction and focus on making a hole down to bedrock at that point. I am generally successful 15 – 20% of the time. My success depends on the depth of bedrock and the size of the material sitting on top. The dredge will only move up to a certain size of rock. The un-vacuumable larger rocks tend to roll down into the center of the dredge hole. Yes I have sucked out trenches so I could move these “pain in the ass” rocks to one side. It is like trying to eat food with only one chop stick. However there are those times when a major gravel seam moves quickly through your dredge because you have hit a “sweet spot”. Either way, the best is when you are finally rewarded by the “clunk” with the suction pipe letting you know you are on bedrock. One piece of advice here: TAKE YOUR TIME! This is where you can pull ounces of gold off the bottom in a very short time span.
Go over this area at least five times as more rocks will keep landing on this newly exposed bedrock due to the rivers current flow while you are dredging back and forth. Keep sucking them up and slowly work your way downstream and I do mean only an inch or two at a time as we use the water flow to our advantage. Some rocks will topple into the depression we have made however as we work our way downstream the current tends to carry loose rocks away from our location rather than into it.
Once the river bedrock is exposed I work the suction nozzle back and forth widening the exposed area. I do this for two reasons:
1) Obviously to recover more gold off the bedrock and
2) With a wider exposed area there is somewhere to roll the bigger rocks when you hit them (and you will). I push these un-suckable rocks with the suction nozzle into an area I have already cleaned. You have to work around rocks that are too big to move, plain and simple. Just do your best when working around those monster rocks.
WHAT TO WATCH FOR
It is likely that you will hit un-mined areas as no one else can reach into the main river channels. As you suction along you may hit patches of “dirty water”. I am talking about what appears to be a blackish dirty material which is very fine that gums up your sluice. Please listen to this very carefully. These spots are honey holes. They are a concentrated build-up of magnetite, garnets and gold. Typically these locations can represent any drop-off, usually ancient locations in the river. Waterfalls from thousands or even millions of years ago, pounding down into bedrock leaving behind an extreme concentration of heavy minerals.
I was working with an old time miner and a diver using a venture style pump in Atlin, BC when we hit one of those spots. The suction tube almost instantly became clogged as black globs of magnetite spewed into the crash box. The old timer up near the shore in the shallow water tending the floating sluice dropped his shovel and started to dance around like a puppet. I thought he had “lost it”. The diver came up because the suction tube was blocked and he saw the miner going nuts in the water. I started slowly backing away because I had no idea what was going on. After about two minutes the miner that was dancing around like a loon started to calm down. He started screaming at the diver that had just come up to the surface. I was calculating the distance between the kooky miner in the water and the rifle he always brought with him, laying on the shore. Could I reach it before him if he completely went off the deep end? An insane man and a rifle don’t mix at the best of times.
Finally he managed to explain what the diver had just found. “You’ve hit a honey hole, damn it!” he said. Then after another minute and an explanation as to what a honey hole was we understood his enthusiasm. The diver had surfaced mad at the jammed suction tube but that was only until he too understood the significance of the find. He had been suctioning out a hole in between two massive rocks about 20 feet under water and had plunged the intake tube down into a pocked he had created by removing material. It was at the base of this hole where he had found this honey hole.
Anytime you come across these blackened magnetite rich areas, be sure to take as much time as needed to clean them out. I don’t care if that is a week or a month. Depending on where you find theses spots along the river and how close the gold is to the source of the eroded material, they can easily contain hundreds of ounces of mostly course gold. I don’t know the reason you got into gold mining, maybe just as a hobby or maybe for some extra cash, but if you ever find one of these locations even when working a high bank placer deposit you can probably consider retiring after you finish cleaning it out. Yeah, they can be that great.
The other thing you will likely find is small gold “streaks”. I have located quite a few that form in fractured bedrock on the bottom of the river, little concentrations of gold that gets trapped in these openings. The best way to extract the gold is to bounce the suction tube straight up and down on top of these spots. The bouncing seems to “pulse” the gold out of its resting place and into your suction tube.
I have intended this “Mining Main River Channels” as a quick introduction to how to get at the rich gold bearing materials that have up to now been inaccessible to 99.9% of all miners. There is nothing more frustration than knowing where lucrative gold deposits are and not being able to reach them. I offer my experiences with dredging main river channels as an option and not as the only way to retrieve gold nuggets from the rivers center.
My view is to have fun and extract quantities of gold from rivers that you come across. It is exciting to unearth both flake and nugget gold as you are working river channels. Really what you are doing is taking your knowledge and labor and converting it to gold and money. I know first-hand that you don’t just walk out there, dig a little hole and collect gold nuggets. You apply experience, probability, labor and a little luck to make Mother Nature reveal her treasures in exchange for your efforts.
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