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how to build nugget traps for narrow river valleys
As gold miners we almost always travel to where the gold is and that makes sense. Sometimes when conditions are right we can make the gold come to us and I’m talking specifically about narrow river valleys that have some sections of exposed bedrock. I discovered this method while nugget shooting a tributary leading into the Fraser River in BC. There was a narrow somewhat rocky section of river that was subject to an intense spring melt. The feeder waters come straight out of the Cariboo Mountains and when spring happens in earnest nature will turn on its fire hose and blast water through this narrow section of river. I knew there had been some nice gold nuggets recovered from this river and had twice worked this narrow section but due to the water flow I would hit this river in August/September. Just before this narrow area there was a somewhat wider river section carpeted with large cobble type stones and some boulders that ranged in size from 2 feet across to a monster one that must’ve been 12 feet in diameter lodged in this stone mixture.
Keep in mind that every area offers it's own unique challenges and advantages. While a narrowing in a river valley can work well, I prefer a younger fast flowing river that pounds down off the mountain side.
HOW TO BUILD NUGGET TRAPS IN FAST FLOWING RIVERS
The key I’ve found is some sections of exposed bedrock in a river bottom with rocky canyons are a first choice of mine. The sheer volume of water moving through the sections can be huge after rains or spring melts and if you watch some larger gravel can settle on bedrock after the main surge of water is over.
This gravel settling is dependent on upstream conditions for this material to the washed into the bedrock areas. Sometimes you can see trace lines of black sand containing gold on irregularities in the bedrock bottom but again it depends on specific conditions.
I was in the Northeast Cassier Mountains in BC when the east side of a mountain valley got hit with a rainstorm. This was in August and the stream I was working had barely enough water to run a sluice box. The storm was just passing over the mountaintop in that valley when the water flow started to increase where I was. At first it was nice to have a little extra water which helped wash away some of the black sand waste gravels and then I could hear what sounded like approaching rapids coming down from the stream head.
The flow surge quickly ran over my rock wing walls I had made to increase water flow through my sluice and there wasn’t time to pull my sluice box out so I threw a boulder in the middle of the capture media to help weigh it down. At the peak flow my sluice box with at least a foot underwater and the quiet stream had erupted into a major torrent of pounding water. This spot I was working was just below a narrow gully that had a mostly bedrock bottom and I was recovering large flake gold and the odd small nugget as I dug down in the rock filled gravel. This rain had happened about mid-afternoon and the stream slow was taking his time going back down. The next day [Yep I had to wait] I dug out my gravel filled sluice which hadn’t washed away thank goodness and notice black sand lines along the bedrock bottom just above where I was digging. These lines were following cracks and fault lines in the bedrock. Yes there was a little small flake gold mixed in but what I noticed was a smaller boulder that had gotten wedged in the rock gully. There were baseball sized rocks immediately behind this rock and I had to check it out. There was about a wheelbarrow quantity of material in total with very small gold on the outer edges and about 12 pieces of rice grain size nuggets just behind the rock. This is where I got the idea for building nugget traps. I have tried the nugget trap just north of a place called “Hell’s Gate” on the west side of the river. To start with there are some bedrock areas in the Fraser River itself in that area and the rivers tributaries can be worked where they enter the river and one of those streams contain some nice color [gold]. Since setting up a nugget trap in the Fraser River is the hardest thing to do I will start there.
1] The first challenge you will face with a large river is building a solid base and that is a rock Ridge that won’t move. I strongly recommend using as large of a boulder as you can comfortably handle.
2] Next you want to find a crack or imperfection in the bedrock bottom so you can build an anchor spot for the rocks to sit against. Way up on the bank is the best spot for this as the heavier gold tends to travel in the shortest line possible. Yes down the center of the river and up on banks on inside curves of the river.
3] If you are dealing with a crack that an inch or bigger first check it for nuggets, second using eye protection and a hammer pounding the largest flat rock that will fit. You want these rocks to stick up out of cracks as far as possible while still anchoring them into the crack.
4] Place rocks just in front of your secure hammered wall. You want them to be no more than one third higher than each hammered rock. The physics of this trap are very important to how it stands up to a high river flow.
5] You want your finished height to be about 10 inches to a foot for a high flow River. I usually keep adding rocks until I reach my target height but remember use rocks no more than one third higher than the previous ones and you want all rocks to touch each other especially the hammered ones.
6] There will be holding your wall suggests place larger rocks to fill in any holes you may have.
7] It’s preferable to have an irregular finish top on your wall. This finish tends to concentrate nuggets just behind the lower wall sections [dips and holes].
8] If you’re working bedrock without any cracks building another trap offers more challenges. You have to have something to secure to, a crack, a small raised section, a seam or something. The key is to create the stop or break on the bedrock surface and then make your nugget trap so it can't be swept away by the river’s current.
9] Other tricks. I have to mention some other things you can try to create almost effortless gold recovery.
A] Follow the bedrock along until you reach the downstream end of bedrock. Bedrock can end a number of different ways:
• A drop-off
• A waterfall
or my favorite
• A gravel stream bottom.
This is generally where bedrock and but not always. If you’re lucky you could hit a bedrock step or simply a tapered bedrock shelf. Either way when the water level is low, dig down along the bedrock/gravel junction. This meeting place generally offers some nice concentrations of gold. As a rule I use black sand as an indicator for gold but not in this junction area because of the particle size and the settling effect. Some gold and most of the black sand will try to settle to the lowest point while flake gold and some flatter nuggets can get caught in suspension along the bedrock junction area. There could be trace amounts of magnetite but generally it won’t be much.
B] You can build your nugget trap just after the visible bedrock ends... But, recovery can be challenging. Bury large rocks about halfway into the gravel as far across the river or stream as you can but be cautious on how high you go because this is in gravel and spring floods will work very hard to “blast” any restriction right out of the way. I built this type of nugget trap once before with mixed results. Put simply, I like to stay on bedrock.
SOME POINTS YOU WANT TO REMEMBER
• You should only build your nugget trap in preferred areas and that means in spots with gold and bedrock.
• If you can position your nugget trap in the path of potential nuggets [on bedrock] so much the better [center of a river, outward bend of the river bank].
• There can be a lot of gold that's moved during spring melts and heavy rains. 99% of the time we work with the results of this movement and not the benefit of the motion. A lot of more experienced miners already know what will stop and catch gold.
• This nugget trap works very well where rivers change course a lot. Shifting gravels, new islands and new sandbars mean more gold for us. The whole idea with these nugget traps is to stop and recover gold without putting out unnecessary effort. This system relies on heavy rocking gravel movement due to floods and serious rains.
• The amount of gold will very year by year based on upstream disruption and sheer volume of water that move our heavy yellow friends.
• Normally you will find the bulk of gold behind our stone wall in the “trap area”. This is dependent on how smooth the front face of our wall is. The largest gold nuggets tend to get trapped in the front of our rock wall as they will be in recesses and holes where water is able to flow through. If the front of your nugget trap is smooth and has no holes after a flood the nuggets will mostly be stuck behind the trap in the low-pressure zone we created.
• If there are a lot of flat stones in your mining area you can build a false bedrock bottom behind your wall. Normally finding in the flat stones is very challenging as gold country is normally glacial worn granites, quartz and harder rock and are not sedentary formations which are primarily flat.