Most all old mine tailings have a per /ton recovery that the owners know very well a lot get looked at in recent times some just dont because to get it out costs so much more than what you get back .
Chasing gold would have to be one of the most time / money things you could embark on with little hope of a win , a simple sluice on the side of a creek lying in the sun on a pleasant afternoon is also part of the fun.