Nvradar--I know this reply is overdue--please forgive the lateness of this post.
Yes, it's tough figuring out the why and when of all those sluice stacks and hand stacks. But, one thing remains true--the old-timers, including the Chinese couldn't see what was in the bedrock. Because of that, they were always covering up gold. True, many of them were efficient, but others were in a hurry to get to the next rush. People get tired too, and they're not always as motivated as their boss is.
I've definitely cleaned crevices in spots worked by the Chinese and got nice gold for my troubles. I've detected bedrock they covered with neat hand-stacked rock walls and got nuggets that were down in the bedrock under those stacks, left there because they had no way of telling the gold was there!
I've worked bedrock (covered with rock piles) left by the regular sourdoughs and the Chinese and got nuggets from both types of workings. You have the modern advantage with your detector. Now for the hard part--get a manure fork, bend the tines (heat before with a torch and then cool quickly after bending) at a 90 degree angle about a third of the way down the length of the tines, then cut off the sharp tips. You'll have a great rock rakin' fork that will be springy enough that you won't jar your arms out of the sockets, and flexible enough to move most of those rocks, but still allow the gold to fall through the spaces between the tines back to the ground you're rolling the rocks away from.
Rake off the rocks and detect the ground under those rock piles very carefully. Eventually you'll find some nuggets and flake gold. It's a tough way to get the gold, but it's there.
Oh, I worked with a guy that uncovered a strip of rich pay once (up in the Yukon) that was under the first stack of rocks in a worked area (that's where the first guys in threw the first rocks to start the original placer mining). It was a narrow strip, but very rich. That happens rarely, but often enough to keep it in mind. I've found little pockets of pay that way as well--little spots that were missed--the material will look very different from the sluff that's falling down through the rock stacks--keep that in mind too, and even if your detector doesn't sound off, pan it out.
All the best,
Lanny
