https://www.dyserth.com/mines.html mentions a 20' waterwheel .
Hi BM, long time - hope you're well!
That's where I saw the 20' wheel reference too. Pity there's no more info.
No sure about water being pumped to the wheel. I see what you mean Morlock, looking at that old Pennant watercolour but I thought that the launder was perhaps taking water to the Newcomen Engine. Perhaps extended past the waterwheel at a later date than the wheels original placement, to feed the engine some house water? (Edit) Though perhaps it provided top-up water supply to the wheel once the pumping engine was operational & surface water was in short supply?
As for the leat system that Euros linked to (same leat as in watercolour?), I'd been looking at that too. I'm sure the place was above the railway course & the bit where the "purple highlighted" leat crosses that area of hillside between the small outcrop (Craig Bach?) & the railway E of the Talargoch engine house looks favourite. There's even a shaft marked on one of the old OS maps - no mine name unfortunately.
Thanks all for the suggestions. Maybe the mines name will remain a mystery!
We inhabit an island made of coal, surrounded by a sea full of fish. How can we go wrong.......