Below is a link to a 64 page document about placer mining from about 1880. I believe it is from the United States Bureau of Mines, but I didn’t see anything that said for sure.
However, it is a great document that every gold miner should read, because it has information on the big and small placer gold mines operating at the time in twelve states and the Dakota Territory. It is important for a modern gold miner to remember that those old timers found only a tiny percentage of the gold in place and recovered even less.
So if there was a paying gold mine in a given area in 1880 that’s a great area for you to prospect, because you know the paydirt is there. It’s just a matter of finding it and with modern gold mining technology it is a lot easier to find than it was when you didn’t have anything but a shovel a pan and burro.
The document also points out where gold miners might encounter diamonds, rubies, and other precious minerals.
Here’s the LINK.
Strike It Rich!