RobinGriffiths
Well-known member
Friday 11 August 2023
About 12 years ago, probably more, I did a Friday afternoon anti-clockwise circumnavigation of Mynydd Mawr starting from Rhyd Ddu. I can't remember much of that trip except that I came across a fenced off flooded shaft on some boggy ground around SH 547 558. Enquiries on the then extant Adit Now lead to a reply from John Mason saying it was a particularly interesting trial with a lot of fluorite in the spoil. Moreover, it contained a suite of rare earths and tellerium rich sulphides derived from the nearby micro-granite of the Mynydd Mawr intrusion.
Fluorite is unusual in this area of Wales, and a return visit was on the cards to have a ferret through the spoil heaps. This didn't get pushed onto the To Do list until recently. Wishing to avoid a long march from Rhyd Ddu and a bog crossing, I spent a while looking for devious shortcuts. Maybe from the North via the woods, or maybe a river crossing near the exit of Cwellyn Lake. Nothing doing. On Friday we bit the bullet and headed out from Rhyd Ddu on the west side of the Lake, easy going until the end of the lake. Here things took a decidedly boggy turn. Although only 500m to the target, it took an hour of stumbling about on and between tussocks of some water loving grass and goat willow. A couple of frogs and a huge Emperor dragonfly enlvined the trudge. Before getting to the target area I noticed an area of spoil to the left at the base of the cliffs at around SH 548 556. This was a different site to the one I had seen before but must be on the same vein. It was on higher ground which was good as I'd had enough of bogs. This would also keep to Open Access land and avoid having to trespass to the original site.
The heap had a lot of 'irony' looking stuff, but a lot of white fluorite as well, with the occasional light green specimen, rarely some purple ones. Closer examination showed that there were also some large brown crystals which on testing with a magnet appear to be magnetite. Also there is some weathered copper staining and some lustrous black crystals, which look like sphalerite. A bit of digging in the spoil also revealed a bonus toad that had managed to surround itself with rocks 6" down. Maybe it got there when it was smaller. It was relocated onto some wet moss for safety. A bit further at the base of the cliff is the 'mine' itself. There's a wide gully coming in from the left down the cliff along the line of a fault, which appears to extend in the direction of the shaft I'd noticed previously. The mine itself is just a flooded overgrown trial. I've no idea about the history of the trial, but there are a couple of online articles on its mineralogy. The tips are interesting, although getting to this location is not easy even in August.
Robin
Castell Cidwm on the approach
Bog Approach
The trial itself. Chucking a rock reveals a flooded excavation - most likely shallow
Abundant white fluorite
Rarer purple fluorite
Some copper staining
Presumed magnetite with quartz
About 12 years ago, probably more, I did a Friday afternoon anti-clockwise circumnavigation of Mynydd Mawr starting from Rhyd Ddu. I can't remember much of that trip except that I came across a fenced off flooded shaft on some boggy ground around SH 547 558. Enquiries on the then extant Adit Now lead to a reply from John Mason saying it was a particularly interesting trial with a lot of fluorite in the spoil. Moreover, it contained a suite of rare earths and tellerium rich sulphides derived from the nearby micro-granite of the Mynydd Mawr intrusion.
Fluorite is unusual in this area of Wales, and a return visit was on the cards to have a ferret through the spoil heaps. This didn't get pushed onto the To Do list until recently. Wishing to avoid a long march from Rhyd Ddu and a bog crossing, I spent a while looking for devious shortcuts. Maybe from the North via the woods, or maybe a river crossing near the exit of Cwellyn Lake. Nothing doing. On Friday we bit the bullet and headed out from Rhyd Ddu on the west side of the Lake, easy going until the end of the lake. Here things took a decidedly boggy turn. Although only 500m to the target, it took an hour of stumbling about on and between tussocks of some water loving grass and goat willow. A couple of frogs and a huge Emperor dragonfly enlvined the trudge. Before getting to the target area I noticed an area of spoil to the left at the base of the cliffs at around SH 548 556. This was a different site to the one I had seen before but must be on the same vein. It was on higher ground which was good as I'd had enough of bogs. This would also keep to Open Access land and avoid having to trespass to the original site.
The heap had a lot of 'irony' looking stuff, but a lot of white fluorite as well, with the occasional light green specimen, rarely some purple ones. Closer examination showed that there were also some large brown crystals which on testing with a magnet appear to be magnetite. Also there is some weathered copper staining and some lustrous black crystals, which look like sphalerite. A bit of digging in the spoil also revealed a bonus toad that had managed to surround itself with rocks 6" down. Maybe it got there when it was smaller. It was relocated onto some wet moss for safety. A bit further at the base of the cliff is the 'mine' itself. There's a wide gully coming in from the left down the cliff along the line of a fault, which appears to extend in the direction of the shaft I'd noticed previously. The mine itself is just a flooded overgrown trial. I've no idea about the history of the trial, but there are a couple of online articles on its mineralogy. The tips are interesting, although getting to this location is not easy even in August.
Robin
Castell Cidwm on the approach
Bog Approach
The trial itself. Chucking a rock reveals a flooded excavation - most likely shallow
Abundant white fluorite
Rarer purple fluorite
Some copper staining
Presumed magnetite with quartz
