Right place, no data! Reading Morrison's Goldmining in Western Merioneth, it seems to be the case that copper production figures, if ever preserved, remain undiscovered. Morrison gives base-metal production (Pb/Zn/Ag) stats alongside gold for some other mines in the district. It's an interesting one: Vigra has evidently seen much work done, and at the stratigraphic horizon in which the lode was worked one would not expect gold to be important, yet there's not a mention of production that I can find.