Martin, it has been my experience that large rocks and high water volume will cause " Boil Out " of flour and fine gold. Also feeding material to fast can blow gold out the back end and I call that the " Hydroplane Effect " because the gold needs time and distance to work it's way down into the riffle traps.

 

     Basically a sluice is tuned by balancing the material size with the water flow ( speed ) along with material feed rate and the fall per foot. ( around 1/4 inch per foot drop on length ) The width should be level across the narrow part of the box so the material flows evenly and does not build up on one side of the box.

 

     Finally the type of trap or traps in the box are what catch the the gold and everyone has their own opinions on what to use including myself. Hope that helps        Ron

     Correction, the fall per foot is around 1 inch per foot not 1/4 inch. Sorry about that.    Ron

Martin,

I would agree with what Ronald has stated.

To answer your question, yes large rocks will dislodge gold out of a river sluice.

Your dredger buddy probably had a grizzly or scalper at the top of the dredge sluice. That allows the heavies to fall through while the large rocks move over the top, thus allowing the heavies to find a home in the box.
Yes water volume is greater dredging, however the slope of the box would be less than a river sluice to accommodate the higher flow, keeping the larger rocks moving.
Using a basic river sluice, you want to classify to what you would expect to see gold size wise. If you expect fly poop size gold, classify to 3/8", I classify everything to 1/2" before I run it. I hope to find that larger than 1/2" nugget, likely no, hopeful yes.
However classifying takes time, time classifying is time lost sluicing = less material moved.

As for putting an exact number on sluice slope, it will depend on water flow.
High flow will equal less slope, low flow equal steeper slope.
The 1" per foot is a starting spot, you adjust as needed.

The recent GPAA magazine had an extensive write up on tuning your sluice, I think there was a write up in a recent Pick and Shovel as well.

I pour my material as close to the top of the box I can, giving the gold as much room as I can to find a home.

Some of us ole dogs can learn new tricks once in a while.

Read and learn all you can from as many as you can.

Fooling around with this gold mining thing for 20+ years, I have never come home with nothing, at times very little, but never nuttin.
Get out there and keep doing it, you learn something new each time.


Bill

Thanks guys! I am ever on the lookout for greater technology and for methods to improve our process. My partner is old school and pretty much poo poos my suggestions because of my limited experience. But, it doesn't keep me from trying!
Martin

Posted By MARTIN SOHLBERG on 04 Jan 2016 08:40 PM

Thanks guys! I am ever on the lookout for greater technology and for methods to improve our process. My partner is old school and pretty much poo poos my suggestions because of my limited experience. But, it doesn't keep me from trying!

Martin

If you want to save time classifying (and effort!), you might take a gander at Trommels. I only recently learned what they were and they look to me to be invaluable for running a sluice at a higher volume of material.