Rhosmynach RIGS site

NRW RIGS no. 573 [SH 48147 91383]

RIGS Statement of Interest:

Rhosmynach RIGS site has been chosen because it contributed to early mining practices and preceded commercial mining at Mynydd Parys. It is marked as a lead mine on the first edition OS map 1841. Mining for copper appears to have gone on at the same time, though never on the same scale as at Mynydd Parys. Mining for pyrite and chalcopyrite ores was carried out in two separate areas, the northern mine being immediately north of Rhosmynach Fawr Farm, while the southern site was nearer to Dulas Bay and the coast. Carbonate and sulphate ores (bluestone) are absent. The country rock is Ordovician shale which is not usually rich in heavy metal ore but the mines are in small outliers of silicified Silurian rock similar to that at Mynydd Parys. The lead ore mined here was richer in bismuth and silver than any other Anglesey site. Traces of gold were also found and more recently tellurium has been identified there. Hammer stones have been noticed at these sites and may indicate prehistoric or medieval mining. Edward Lhuyd reported mining activity here around 1695 and the mines were productive at the mid 18th century, John Owen and Alexander Frazier actively extracting ore here in 1760 prior to the discovery of the Great Lode at Mynydd Parys. This important site emphasizes the widespread and vigorous exploitation of domestic copper resources beyond Mynydd Parys after the mid 18th century introduction of full copper hull sheathing especially of warships.

Geological setting/context: There are three main categories of RIGS selected for their historical importance: 1. Historical constructions (arbitrarily up to 2,000 years old) and/or archaeological constructions (arbitrarily more than 2,000 years old) where rock has been used and where the relevance of geology can be demonstrated. This type of RIGS can include castles, churches, ruins, lanes, walls, cromlechs and standing stones. 2. Sites or features related to the development of geological thought and geology as a science, such as sites where certain concepts or theories were developed or types of feature first explained (e.g. Hutton’s Unconformity). 3. RIGS commemorating the work and contributions of important geologists. These usually take the form of a monument (such as a grave) or memorial. Network context of this site: Rhosmynach Mine has been selected as an historical RIGS as part of category 1 (see above). Although the site was possibly exploited in prehistory, its documented history is post-medieval, possibly earlier than Mynydd Parys.