the heavies drop out in the first riffle - I think you may not know but the first riffle, although it looks like it is clogged, usually turns over the most capturing the gold that drops out first. the water will do the washing and the churning and stratify the material putting the gold on the bottom of what you see clogging it up, or on the top.

now if you are running the sluice all day or for extended periods over an hour or so you can use a magnet in a Zip lock baggie or a medicine prescription bottle ( so you can get the black sand to release from the magnet when you want it to, just pull the baggie away from the magnet or flip the bottle upside down and it will drop off )while running the sluice in the water, waive the baggie or bottle over the material in the first riffle and it will grab all the heavy black sand and stick to the magnet. Take that to your pan and separate the baggie to release the black sand in your pan to pan. sometimes when you use a magnet it clumps the black sand and if there is gold in that clump it will stick on the magnet with the clumped black sand. Gold is non magnetic but when it is grabbed onto by the black sand it can get picked up so always check your black sand. I keep all my black sand concentrates from the year and at the end of the year I turn it in a small cement mixer with a few drops of Mercury and capture the gold that I could not see.

some guys use a magnet in a pvc pipe closed off at both ends and the magnets slides inside - one of the GPAA members makes them and sells them at the GPAA Gold Show - I got one from him and have used it for about 15 years now and love it.

good luck friend - Happy Thanksgiving- Be sure to give thanks to God above for the many blessings and good food.
your friend and fellow GPAA member
Don Greeno

I will offer this,
If the material behind the first riffle is "dancing",
as Don describes the water is doing the stratifying of heavies, the gold will work it's way to the bottom
If not dancing, adjust the water flow or angle
With my 11" w x 27" L sluice, when I drop in a scoop of 1/2' material, I normally see about 20ish seconds before the second riffle mostly clears
I will knock the larger stones out periodically
The area I hunt, I dont see a large amount of black sands. If heavy black sands yes try to clear

Bill