Applied Earth Science Division visits historical copper mine

4 Oct 2017

On 17 June 2017, the members of the Applied Earth Science Division (AESD) had the opportunity to visit the historical Parys Mountain copper mine on the Isle of Anglesey, Wales.

The mine worked between 1768 and 1904, where approximately 3.5 million tonnes of ore yielded 130,000 tonnes of copper metal. Around 20km of tunnels were excavated. The primary mineralisation comprised pyrite, followed by a chalcopyrite-dominated phase and then a sphalerite-galena dominated phase known as “bluestone”. These distinct phases are believed to have formed from exhalations on the sea floor, analogous to black smokers seen today. The deposit is considered to be of the Kuroko type and as such, is unique in the UK.

On arrival, the members first observed features of the extensive acid mine water lakes surrounding the area. These are reminiscent of an abandoned copper mine in Cyprus. With the vivid red colour of the water, and past chemical analysis, the pH levels are determined to be around 2. It has been said that in the past, people used to dip their finger into the water and taste it, burning their tongues. This is no longer recommended as arsenic is also present in the waters.

Once we had finished viewing the surface features, it was time to kit-up with helmets, cap-lamps and safety boots and to travel underground. Many of the 45 fathom tunnels were low, which required most of the party to crouch to pass through. Climbing the Victorian ladders and spiral stairs, and passing over planked platforms, provided an adrenaline rush while appreciating the mine history.

The majority of the party were mineral enthusiasts interested in Parys Mountain’s hidden gems. These included the ubiquitous stalactite formations hanging from the tunnel roof. Of particular interest was the presence of so-called ‘Snottite’, which is a mucus-like microbial mat of single-celled extremophilic bacteria that forms on the old mine timbers. A light blue mineral was found in selected chambers covering the pyritic wallrocks. This was the mineral Pisanite, an iron sulphate first described at Parys Mountain in 1895. Elsewhere, green secondary copper minerals are found on roof timbers.

It was a great tour for all and provided younger professional members with an appreciation of the intricacies of historical mines. Everyone gained from the opportunity to learn about the history of Parys Mountain.

Chloe Lam, AESD committee member