- Hydrothermal: alpine type veins
- Hydrothermal: mesothermal polymetallic veins
- Hydrothermal: volcanogenic massive sulphides
- Cae Coch Mine, Trefriw, Gwynedd: pyrrhotite occurs predominantly in numerous quartz-pyrite veins cutting basic volcanic rocks in the footwall of this bedded pyrite deposit (Ball & Bland, 1985).
- Clogau Mine, Bontddu, Gwynedd: although a mine within the Dolgellau Gold-belt (see below), Clogau deserves a special mention as pyrrhotite also occurs there in late, syn-tectonic low-angle alpine fissure-type veins which cut the gold-lodes in places. Unlike the occurrences in the gold-lodes themselves, in this association the pyrrhotite is often euhedral, forming tabular pseudohexagonal crystals to a few millimetres across associated with arsenopyrite, chalcopyrite, chlorite and rutile in a quartz-carbonate matrix.
- Dolgellau Gold-belt, Gwynedd: pyrrhotite occurs abundantly in the mesothermal gold-bearing quartz lodes of this metallogenic province. It is associated principally with chalcopyrite in a quartz and carbonate matrix and forms anhedral masses often several centimetres across. It post-dates arsenopyrite, pyrite, gold and tellurides but pre-dates the again widespread galena and sphalerite (Mason et al., 2002). Occurrences can be found at virtually every mine and trial in the area.
- Dylife Mine, Penegoes, Powys: one of only two localities for pyrrhotite in the Central Wales Orefield. Pyrrhotite occurs on the tips opposite the Star Inn at Dylife but is very rare. The occurrence belongs to the late (A2) group of Mason (1994; 1997) and pyrrhotite is present as tabular crystals to 7 mm across in cavities in quartz, with galena in association. The occurrence was first documented by Jones & Moreton (1977).
- Erglodd Mine, Talybont, Ceredigion: pyrrhotite is very rare in Central Wales and this is one of only two localities. It occurs very rarely associated with galena, sphalerite, chalcopyrite and siegenite as aggregates in quartz to ca. 1 cm in diameter. The assemblage belongs to the early or A1 group in the regional paragenesis (Mason, 1994; 1997).
- Parys Mountain, Anglesey: the presence of pyrrhotite here was recorded by Pointon & Ixer (1980) as microscopic rounded inclusions associated with chalcopyrite in pyrite and as slightly larger aggregates replacing pyrite.
- Snowdon, Gwynedd: Snowdon Caldera copper-veins: although rare in the central part of the caldera (Reedman et al., 1985), pyrrhotite occurs frequently in mines in the outer and marginal parts of the caldera, especially in the area from Bethesda-Llanberis-Nantlle-Cwm Pennant, where it is often associated with chalcopyrite and arsenopyrite. It is clearly later in formation than the arsenopyrite, euhedral crystals of which it commonly encloses. It is always massive and may have a granular, recrystallized texture due to later deformation.
- South Wales Coalfield: pyrrhotite is an uncommon component of the septarian ironstone nodule-hosted sulphide assemblage, better known for its millerite specimens. Hexagonal platy crystals were recorded from Parc Colliery, Cwm Parc by Firth (1971), while more recently specimens have been found at tips derived from the Gelli and Ferndale collieries in the Rhondda Valley (I.E. Jones, unpublished data).
- Tyllau Mwyn, Drws-y-nant, Gwynedd: pyrrhotite occurs as tabular crystals in calcite-dominated stilpnomelane-bearing veins cutting a metamorphosed bedded ironstone deposit at this locality high on the flanks of Aran Fawddwy (Matthews & Scoon, 1964).
- Allen, P.M. & Jackson, A.A., 1985. Geology of the country around Harlech. Memoirs of the British Geological Survey. Explanation of sheet 135, with part of 149, 112pp.
- Ball, T.K. & Bland, D.J., 1985. The Cae Coch volcanogenic massive sulphide deposit, Trefriw, North Wales. Journal of the Geological Society, London, 142, 889-898.
- Bevins, R.E. & Mason, J.S., 1998. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Gwynedd. National Museums of Wales, Cardiff.
- Firth, J.N.M., 1971. The Mineralogy of the South Wales Coalfield. Unpublished Ph.D. thesis, University of Bristol.
- Jones, J.A. & Moreton, N.J.M., 1977. The Mines and Minerals of Mid-Wales 40pp.
- Mason, J.S., 1994. A Regional Paragenesis for the Central Wales Orefield. Unpublished M.Phil thesis, University of Wales (Aberystwyth).
- Mason, J.S., 1997. Regional polyphase and polymetallic vein mineralisation in the Caledonides of the Central Wales Orefield. Transactions of the Institution of Mining and Metallurgy (Section B: Applied Earth Science), 106, B135-B144.
- Mason, J.S., Bevins, R.E. & Alderton, D.H.M., 2002. Ore Mineralogy of the mesothermal gold lodes of the Dolgellau Gold Belt, North Wales. Transactions of the Institution of Mining and Metallurgy (Section B, Applied earth science), 111, B203-B214.
- Matthews, D.W. & Scoon, J.H., 1964. Notes on a new occurrence of stilpnomelane from North Wales. Mineralogical Magazine, 33, 1032-1037.
- Pointon, C.R. & Ixer, R.A., 1980. Parys Mountain mineral deposit, Anglesey, Wales: geology and ore mineralogy. Transactions of the Institution of Mining and Metallurgy (Section B: Applied earth science), 89, B143-B155.
- Reedman, A.J., Colman, T.B., Campbell, S.D.G. & Howells, M.F., 1985. Volcanogenic mineralization related to the Snowdon Volcanic Group (Ordovician), Gwynedd, North Wales. Journal of the Geological Society, London, 142, 875-888.
- Thorpe, R.S., Williams-Thorpe, O., Jenkins, D.G. & Watson, J.S., 1991. The geological sources and transport of the bluestones of Stonehenge, Wiltshire, U.K. Proceedings of the Prehistoric Society, 57, 103-157.