Trychiad Ffordd Moel Hafod Owen
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Geology & landscape
Geological Period: Ordovician · Rock Type: Breccia, Mudstone, Siltstone
Description
Description Trychiad Ffordd Moel Hafod Owen is of special geological interest and is situated in the heart of Coed-y-Brenin, approximately 1km north of Capel Hermon and 9km north-north-east of Dolgellau. Occupying a relatively high structural level above the Coed-y-Brenin porphyry copper deposit are a number of intrusive breccias which form pipe-like bodies attributed to epithermal fumarolic activity during the waning stages of Rhobell Fawr volcanism in early Ordovician (Tremadoc) times. The excellent trackside exposure on Moel Hafod Owen is of special interest because it provides the best example of a mineralized breccia which, at this locality, consists of highly bleached, silicified and pyritized clasts of siltstone and mudstone set in a quartz-and pyrite-rich matrix that is geochemically enriched in arsenic, antimony and gold.