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I wrote this post for a thread on Alaska Gold Forum. The information may help you recover more of the fines.When designing a sluice experience has taught me to have plenty of water running over your biggest rocks. This will lesson the weight of the rock by the amount of water that the rock displaces. I figure the largest rock that I want my business end to ingest and add an inch or 2 of water over the top. Also, the water flowing over the top of the rock adds lift much like the wing of an airplane and the pressure difference between the upstream and downstream sides all add to the ease of transport through your sluice. The second thing that you need to take into account is the riffle system. I personally think Hungarian riffles are only good for coarse gold. Anything smaller than 1/16" will migrate down your sluice and over the end. In my early years I had an expanded metal in my sluice that worked very well. This was a 2" x 16ga decorative sunshade for office windows. I haven't seen it for years and I don't know if it is still made. The last dredge I built was a 4" er and I put Monsanto's door mat material in it. This has stiff plastic 8 bladed tuffs in rows and they are bent in different directions. You should be able to buy them at your local Freddy's (or other hardware store). Straighten the blades out by diping the blades in boiling water for a second or two. Don't wet the backing. Next at 4 to 6 inch intervals perpendicular to water flow cut one row of blades down to the backing leaving just the base button. These will be your nugget traps. My sluice was 10" wide and 8 feet long with 4- 10" x 2 foot long removable mats. I never found much fine gold in the last section. Tests confirmed capture of 98% of 200 mesh and 95% of 300 mesh and this was Snake Rivers popcorn gold and platy gold. This combo will allow slower water in your sluice and additional length will give the fine gold time to settle to the bottom. The rocks will strike the blades and move the black sand and the fine gold that has sought refuge behind the blades will sink out of the current and be trapped until you remove and turn it upside down in a pan or bucket. One word of caution. The additional weight of the water and black sand etc. coupled with the additional length will require additional structural design considerations. Good luck and happy hunting.
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