Your interesting question stimulated me to try to find out more.
An excellent summary of epithermal gold deposits can be found at: http://www.sprottglobal.com/natural-resource-investing/investment-university/
It probably has more answers than you might need, but I think it gives a great overview. One type of epithermal gold deposit indeed has the silver at depth and the gold above, as you asked.
(I looked at two texbooks, and ten or more websites; the SprottGlobal website is the best source of info that I found.)
