Years ago, I talked to a couple of older fellows in the heart of the Cariboo in BC. One tidbit they told me was the dredge on Antler Creek only sluiced material that was -2". Anything larger was immediately discarded. There are long rows of large loose cobbles, so this makes sense. The other comment was someone on the crew once noticed what they thought was a large nugget falling out into the pile, but they looked hard and never found it. This was on someone else's claim, so while I wandered through many times, I never prospected or detected the tailings there.
I recall reading that one method for hunting these kind of tailings, is to set up a bench with the detector on top and the coil off the ground. Then slowly take the cobble pile apart and run any interesting pieces by the coil before discarding. Also detect any of the loose dirt or clay in your hole, because over the years any dirt that remained on the top cobbles washed lower and accumulated here and there. The problem in that location is these stacks of cobbles were mostly dumped into the dredge holes as the bucket dredge moved forward, so the cobble piles are like icebergs with the exposed portion being 10-20' high, but probably go down to depth of over 40'. In that area, you can hear the stream running through them out is sight, so digging down will pretty quickly run into an underground stream.
