Mwyngloddfa Pennant
Geology & landscape
Geological Period: Carboniferous, Silurian · Rock Type: Limestone
Description
Description At Mwyngloddfa Pennant, vein mineralization of Mississippi Valley-type affinities is hosted by Silurian mudstones and shales. As in the NE Wales Orefield, the chief metalliferous minerals are galena and sphalerite, with minor chalcopyrite. In contrast, however, barite and witherite are the chief gangue phases and were present in sufficient quantities to have been mined in their own right. Barium minerals only occur in trace quantities in areas of the orefield underlain by limestone, which makes their abundance here all the more interesting. Mwyngloddfa Pennant is of considerable scientific importance because it is possible that the vein deposits represent a development of the NE Wales Orefield mineralization within the subjacent Lower Palaeozoic basement. If proven to be correct, this would challenge current opinion that the Mississippi Valley-type mineralization occurring within the ‘Pennine-type’ orefields of Britain is confined to Carboniferous and younger carbonate-dominated, shallow water sedimentary sequences. Remarks Mwyngloddfa Pennant was selected following the completion of a joint research initiative undertaken on behalf of CCW by the National Museums and Galleries of Wales. The site is a revision to the former Nature Conservancy Council’s ‘Geological Conservation Review’, a national survey and evaluation of sites of geological and geomorphological interest. The site is described in the forthcoming GCR volume entitled ‘Mineralization in great Britain’ (Bevins, R.E., Young, B., Mason, J.S., Manning, D.A.C. & Symes, R.F. 2010. Mineralization of England and Wales. Geological Conservation Review Series, No. 36, JNCC, Peterborough). The site lies within the Clwydian Range AONB.