Classification is the key to any successful recovery of values in any piece of equipment, no matter what it is.
At Virginia City, Montana about 35 years ago, there were thousands and thousands of tons of old tailings piles left by the dredgers. At that time I had a D-Tex metal detector and went one weekend to search those old piles. Because those dredgers were set up to classify all materials to be processed down to 1/2" mesh through their trommels, any gold larger than that would be dumped out with all the oversize burden. This happened in Alaska and elsewhere also.
Well to make this short, I found about 20 chunks of gold that weighed over 1 lb each and a whole lot of over 1/2" nuggets. At that time, gold was cheap so I only made about $40,000 on that weekend trip. (Good money back then!) I figured that not too many people had ever thought to work that particular area with a MD before and I must have been correct. My deepest dig was about 1 2/2 foot as those old detectors did not go near as deep as these new ones do.
Unfortunately, I never got back to that area, as I had another job to do in another state far away and just never got back until a few years ago. Needless to say, nothing looked the same at all, and some of the locals told me that several outfits had been in since I had been there and "cleaned up" millions in gold left behind by the old dredgers.
Anyhow, classification is extremely important, and every class should be checked for the amount of gold in it, then determine your best zones of classifications and set up to run each one separately if you intend to go this route.
I mainly like hardrock type deposits, but a good placer still gets my blood to pumping good also!

Comanchero