Outside on the park is the Paymaster Stamp Mill, the only fully operational, steam-operated gold quartz mill using restored original equipment.
From the boston.com
The quartz was then crushed into a fine dust by stamping batteries in a stamping mill.
From the en.wikipedia.org
It is likely that a water-powered stamp mill was used at Dolaucothi to crush gold-bearing quartz, with a possible date of late 1st century to early 2nd century.