Homemade drop riffle questions?

[Caminochaos]

I found a 2x8 laying around and cut it to 5' long to make a drop riffle sluice. I have access to all the wood tools you could imagine. This drop riffle sluice will be the perfect width for my little Tanaka water pump.

1. How wide and deep should I make the drop riffle?

2. How far apart should the riffles be?

3. Should there be any other riffles/nugget trap to agitate the dirt?

4. What is the best design for the riffle? Should there be a 45 degree cut on the end of the riffle?

 

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[prospectordamon]

before anyone can acurately answer your question we need to know what type of gold is found in the creek/stream you are prospecting (course nuggets, smooth flakes, flour gold, etc.)


I'm facing the same delima with my sluice box project, trying to figure out how to fabricate a pivoting riffle tray

 

[Gravelwasher]

To see the gold size being found check, pics of sluicing, Camino and I found some of this, but hopefully the sluice that will capture fine gold will surely hold coarse gold. I know my sluice will catch -100 mesh to a couple of gram lead bullet, drop an ounce nugget in and it should stay where it landed. So in general what is the best pattern size depth etc?

 

[Astrobouncer]

If you want to build a drop riffle so you dont have to classify you want to make about four 1/8 inch wide cuts spaced about 1/4 inch apart at first at least 5/16s inch deep, but deeper is fine as well, this is to catch the very fines, and the small width will keep any bigger rocks out leaving these riffles to hold the fines. Deeper cuts are ok if you are going to be bank running material, in fact I like to go with 1/2 inch on these if there is room. You can go with more of these, if the majority of your gold is fines.

I would make some (at least 4) 3/8ths inch wide cuts next then make at least four 1/4 inch wide cuts, both of them at least 5/ 16ths deep, keep them all about 1/4 inch apart as well. These will also capture very fine gold and hold on to it, but it will clean the riffles better then the 1/8 inch wide drops.

Just keep those first drops straight U shaped to hold the fine gold. Then after all those, you can start doing funky cuts. Reverse riffle works great, also the 1/2 inch riffle with a deeper 1/8 inch groove cut into it is another one I like. Another good one is the straight old V cut.

Just keep cutting the drops slightly wider, then towards the end of the sluice make then an inch or two wide to catch any misc heavies like nuggets. If you build it right, you can bank run the material and not have to classify it at all. For width I would go no wider then 11 inches for easy cleanup into a bucket (bucket is about 11 and 1/4 inch wide). As to how far apart to make the riffles, well the farther apart they are the more space you are wasting. You want as many drops as possible in there to capture as much material as possible. The more you capture the longer you can go between cleanups.

Here's some pics of my one drop riffle sluice which I had behind the Angus Mckirk dredge today, and it worked great. Big rocks would roll right on out of it. Bank running material was no problem with it.

Heres some examples of what I am talking about, notice the smaller grooves inside the other ones.









I will upload some pics + video of my drop riffle behind the Angus Mckirk dredge from today (my sluice works great with up to 3 inch rocks which roll right on out) soon as my camera battery is charged enough to upload.

 

[Gravelwasher]

Astro Nice Job and good info!!! Thanks


You got a dredge? You lucky Sucker!! We have that dam ban everyone keeps overloading the sight with political talk about. So your lucky to be able to dredge. Suck on!!

 

[Astrobouncer]

Here ya go fellas here's video of my long tom drop riffle behind the dredge from earlier today, it works great and will easily handle up to 2 1/2 inch rocks with no classification.The first cleanup in it showed we were only losing some fines, 100 mesh and smaller out of the dredge in about 2 hours run time. Second cleanup showed a couple 30 to 40 mesh which were really flat and thin, and about ten 60 to 100 mesh in about 2 1/2 hours. Its not my dredge but my prospecting partners. Its one of those angus mckirk chameleon 2 1/2 inch dredges, which is about perfect size for the creeks we work since its quite a hike to bring it to the creek. We still have to put a damper on the back side of the crash box to calm down the water turbulence, the problem is the pump is way too much GPM (we been running at least 75 gpm when it really only needs about 40-50) for the drop riffle, so we been diverting some water with the smaller hose which helps out for about 5 psi. Also the water flow on this creek is actually a lot smaller then it looks here, as this is one of the few parts of the creek with decent water. Most of it is inch high so we cant really use a much bigger dredge as easily.



The enviro-nazi's haven't got to us out east here yet. Most of the prospectors in this state that I know try to keep a low profile and work only private property away from the prying eyes of big brother.

 

[Caminochaos]

Thanks for all your help astro. I tried cutting out a 1x6 but after we plained it it was only 5/8" thick. I used a skil saw to make the cuts but it was a pain in the butt to chisel out the grooves without breaking through the bottom. I had a 2x8 laying around that will split to 3/4" and being only 7 1/4" should be perfect width for my little pump. It will be 5' in length. I just hope the wood isn't rotted through or I may have to just buy a 1x8.

 

[Caminochaos]

before anyone can acurately answer your question we need to know what type of gold is found in the creek/stream you are prospecting (course nuggets, smooth flakes, flour gold, etc.)


I'm facing the same delima with my sluice box project, trying to figure out how to fabricate a pivoting riffle tray

See all of the above. I have found up to 1 gram nuggets to small fly poop. It's got to be pretty versatile.