Benallt Mine and Nant y Gadwen
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Geology & landscape
Geological Feature: Rock Outcrop
Description
Description Benallt Mine and Nant y Gadwen are situated in west Llyn, North Wales, some 5 kilometres east of Aberdaron around the village of Rhiw. The site consists of two discrete localities. Benallt Mine lies to the north of the Aberdaron to Rhiw road on the southern slope of Mynydd Rhiw and consists of an opencast site, around 16 shafts and many small dumps of spoil. Nant y Gadwen is a small valley to the south of the narrow south-west trending valley to the south of the Aberdaron to Rhiw road. This valley contains an important fossil locality as well as the Nant Mine. The Benallt workings, while no longer providing an outcrop of the manganese ore body, contain specimens of a wide range of manganese and barium bearing phases. Included in this mineral assemblage are cymrite, pennantite, grovesite and banalite, all of which were first recorded from this locality; in addition, the celsian and paracelsian from this site were the first occurrence of these minerals recorded in Britain. Although a wealth of mineral data has already been produced, it still has great potential for paragenetic and petrographical work. Nant Mine similarly has no outcrop of the manganese ore body, but in contrast to Benallt, has a strong carbonate component in the paragenetic sequence. In addition, whilst the assemblage also displays a manganese silicate content, iron and manganese oxides of primary origin form a significant proportion of the ore. Together Nant and Benallt mines form part of a laterally zoned sequence vital to the petrographic study of these ores. As well as Nant Mine, the Nant y Gadwen valley provides one of Britains most important Arenig sites, being the only place in North Wales where the three divisions of the Arenig Series can be proved palaeontologically. The lower Arenig sandstones and middle Arenig tuffaceous rocks yield a rich trilobite and graptolite fauna (including taxa known from the Chinese faunal province). The overlying tuffs and siltstones also contain trilobites and the most important British upper Arenig graptolite fauna. The fauna is rich and varied showing affinities with fauna known from Spitzbergen. The exceptional preservation is of importance for the study of the evolution of the early graptoloidea.If you require a full legal copy of the document please contact CCW in writing.