You should pay a visit to the Welsh Klondike or the Dolgellau Gold belt.
There are many old mine workings, mainly along the bottom reaches of the Rhinog range nearer to Barmouth.
Ive walked past a few of them, but have left them alone, as their not a place to visit without company., and being in a remote region on the Park, if i got into difficulty, it would be game over.
According to the publication written by GW Hall, titled "The Gold Mines of Merioneth", there are still considerable amounts of gold ore still to be mined in the region, and recently in the Western Mail, the company that own the rights to most of the mines, have shown recent interest in reopening one of them.
The only problem, is that they require an act of Parliament for permission to reopen and mine them. and the last serious attempt, was way back in 1915
If exploring old mine workings is your thing, and wanting a good excuse to visit a very special part of Snowdonia, the area above Plas Y Brenin forest, is the place to go.