Gravity Separation & Concentration Methods

Hi Mike,

Thanks for uploading the video above, that shows how a riffle works. It was nice seeing it - how it works.

It appears to be inefficient, though ... the design - lacking in understanding.

May I offer a new idea that should be looked into:  "Scallops".

This is the way Mother Nature appears to do it. Maybe, we should follow her lead here.

In figure 1, note the flow of the water - off the final 'lip edge' of the scallop. The water's flows 'jump', is going to cause a low-pressure cell inside the trough of the next underlying, following scallop ... which will pull down the water jet (with its entrained solids of sand, fines and gold).

The gold, being heavier, will settle downward in the flowing stream of water - so far downward, as to be picked up by "the reversal water current" blowing backward and upstream against the main currents direction. (You have a permanent 'rotor' set up here.)

Meanwhile, the lighter density sands and fines should still be entrained within the water jet and in going forward, "launched" over the next scallop's trough, etc., etc., etc.,

It looks like a better, cleaner way to separate placer gold ... Nature's way. It would be worthwhile to do some design engineering calc. and then collect data from running some test experiments.  

https://caves.org/pub/journal/NSS%20Bulletin/Vol%2036%20num%202.pdf

Many different riffle patterns have been tried, with varying amounts of success.   In this instance I was not trying to propose a particular design, but rather to show how water flows over an obstruction to create varying velocity area and thus settling areas.

Riffle size and selection is entirely dependent on the size and amount of material you want to recover.  No one design works in all applications.  But the general principal is the same.