Trychiad Ffordd Craig Fach
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Geology & landscape
Geological Period: Ordovician
Landscape processes: Volcanic / Igneous
Description
Description Trychiad Ffordd Craig Fach is of special geological interest and is located on the south-eastern flank of the Moelwyn range of mountains, approximately 400m east of Llyn Stwlan and 900m west of Tan-y-Grisiau Reservoir. The locality is of special interest for the study of sulphide-rich, lead-zinc-copper vein mineralization in the Ffestiniog-Porthmadog Belt. The NE-striking vein, hosted by Ordovician (Arenig-Caradoc series) mudstones, is rich in sphalerite and galena within a quartz-chlorite gangue. Field, textural and compositional evidence suggest that the veins are more likely to be linked genetically to the mineralization in and around the Snowdon Caldera, rather than to the Dolgellau Gold-Belt. The locality is of critical importance because deformation structures, including boudinage and internal cataclasis, provide clear, but rarely exposed evidence that the vein mineralization is pre-tectonic with respect to the Acadian (late Caledonian) compressional deformation.