Perhaps the most notable thing about skim placers is that they form on the top surface of gravel bars, as opposed to coarser gold placers where the weight of the gold particles allows the gold to settle down on or near bedrock.

While recovery rates are important, they must necessarily be secondary to the volume of material processed. Running more material at lower recovery rates is generally preferable to increasing the efficiency of the system.

When I teach people about finding gold, I often explain that it is helpful to think of any river or stream that carries gold as being something like a sluice box.