Chalcopyrite

Crystal System: Tetragonal
Status of Occurrence: Confirmed Occurrence
Distribution: Widespread
Chemical Composition: Copper iron sulphide
Chemical Formula: CuFeS2
Method(s) of Verification: chalcopyrite is readily identified visually, both in hand specimen and in polished section.

Chemical Group:

  • Sulphides

Geological Context:

  • Hydrothermal: alpine type veins
  • Hydrothermal: Mississippi Valley Type veins
  • Hydrothermal: mesothermal polymetallic veins
  • Hydrothermal: epithermal polymetallic veins & pipes
  • Metamorphic: skarn mineralization
  • Hydrothermal: volcanogenic massive sulphides
  • Sedimentary
  • Hydrothermal: sedimentary exhalative deposits
  • Hydrothermal: porphyry-type mineralization
  • Hydrothermal: copper-dolomite
Chalcopyrite on dolomite from the Great Ormes Head. Specimen 13.5 cm across, National Museum of Wales Collection (NMW 77.35G.M.47). Photo M.P. Cooper, © National Museum of Wales.
Chalcopyrite (yellow) filling cracks in shattered arsenopyrite (pale grey). Ffridd-goch Mine. Microscope image of polished section. Field of view 1mm. Specimen J.S. Mason, © J.S. Mason.
Chalcopyrite (white) as rods in sphalerite (black). Two rows of siegenite (top) are also present. Chalcopyrite present in sphalerite with this texture is is known as 'chalcopyrite-disease'. Microsope image of polished block. © J.S. Mason.
Chalcopyrite, from Dolyhir Quarry, in a typical massive form, with a golden-yellow colour, slightly tarnished in places. Specimen J.S. Mason, © J.S. Mason.
Chalcopyrite tetrahedra, Caerau Colliery. Maesteg. Crystals up to 0.5 mm cross. Specimen National Museum of Wales (NMW 73.9G.M.55.1), ex J.N.M. Firth Collection. Photo M.P. Cooper, © National Museum of Wales.
Introduction: chalcopyrite is the principal ore of copper. It occurs in a wide variety of primary ore deposits, from medium-temperature mesothermal lodes and porphyry-style mineralization to low-temperature Mississippi Valley-type deposits.It also occurs as a diagenetic/low-grade metamorphic mineral. Chalcopyrite, like many sulphides, tarnishes readily on exposure to air, the colours varying but often including blues, greens and purples. In such a state it has frequently been mistaken for bornite in the past. Its rich golden yellow colour when unweathered is enough to readily attract attention wherever it is seen in a freshly-broken rock sample. In fact, when present as small, 1-2 mm flecks in white quartz, it is a more potent 'fool's gold' than pyrite, the mineral to which that nickname is more commonly applied.
Occurrence in Wales: chalcopyrite has been an important mineral to the Welsh mining industry for centuries; it was the chief economic mineral at Parys Mountain Copper Mine, in the mines of the Snowdon Caldera and, to a lesser extent, in the Dolgellau Gold-belt and the Central Wales Orefield. At Great Orme Mine near Llandudno, the deeper 19th century workings were for chalcopyrite (the older, upper workings having largely worked the oxidized zone). The majority of the hundreds of metalliferous mineral veins known to exist in Wales contain chalcopyrite in trace to major quantities; moreover it occurs in places as fine disseminations through some very extensive bodies of rock, as in the unworked Coed-y-Brenin porphyry-copper deposit near Dolgellau. It is also present as a diagenetic mineral in ironstone nodules across the South Wales Coalfield.

Key Localities:

  • Central Wales Orefield: ubiquitous in trace to minor amounts, chalcopyrite was locally present in sufficient abundance in this area to make its mining a viable proposition. Copper concentrates were produced from a number of mines, including Dylife, Dyfngwm, Geufron, Snowbrook, Nantyricket, Dalrhiw, the Darren mines, Eaglebrook, Esgairfraith, Erglodd, Dolclettwr and Ystrad Einion (Jones, 1922). Very occasional euhedral chalcopyrite crystals have been recorded from quartz-lined cavities in breccias present on mine-tips at Brynyrafr, Darren, Cwmsymlog and Erglodd mines, but the mineral is in most cases massive. Associated sulphides are galena, tetrahedrite, bournonite and ullmannite (Mason, 1997); chalcopyrite is also common as inclusions in early generations of sphalerite in the texture known as 'chalcopyrite-disease'.
  • Dolgellau Gold-belt, Gwynedd: chalcopyrite is ubiquitous in the mesothermal gold-lodes of this area (Mason et al., 2002) and was abundant enough at some mines to prompt attempts to mine it commercially, as at Panorama, Clogau, Old Clogau and Vigra. However, copper mining in this area rarely proved to be viable due to the low grade of the ore and the commonly intergrown worthless iron sulphides. The most important copper producer was Glasdir Mine, which worked a mineralized volcanogenic breccia-pipe as opposed to a lode: here, chalcopyrite occurred as a breccia cement with pyrite and considerable tonnages were produced up to the outbreak of the First World War (Hall, 1990; Allen & Easterbrook, 1978). Within the Gold-belt there also lies the unworked Coed-y-Brenin porphyry-copper deposit, discovered in the late 1960s, in which disseminated and veinlet chalcopyrite is associated with tennantite, bornite and other minerals (Rice & Sharp, 1976).
  • Dolyhir Quarry, Old Radnor, Powys: chalcopyrite is an important component of the tennantite-galena-barite dominated primary assemblage present at this locality, in veins cutting both Silurian limestones and underlying Precambrian rocks (Bevins & Mason, 1997).
  • Great Orme Copper Mines, Llandudno, Gwynedd: well-formed tetrahedral chalcopyrite crystals, perched on crystalline 'saddle-dolomite', are well-known from the unoxidized part of this extensively-mineralized area of Carboniferous Limestone. The paragenesis is one of very few examples of the 'copper-dolomite' association known in the UK (Ixer & Davies, 1996).
  • Halkyn Mountain, Clwyd: chalcopyrite is a widespread minor component of the Carboniferous Limestone-hosted Mississippi Valley-type mineralization developed in this area. Typically it occurs as scattered euhedral crystals embedded in clear crystalline calcite, but is often oxidized to copper carbonates (Bevins & Mason, 1999).
  • Parys Mountain, Anglesey: chalcopyrite was the principal source of copper at this mine and is also a significant component of the 'bluestone' reserves identified by recent drilling (Greenly, 1919; Pointon & Ixer, 1980). The ore was deposited from hot fluids exhaling onto the sea-bed, much in the same way as is observed today in underwater 'black smokers'. Associated minerals include pyrite, galena, sphalerite and a host of minor species.
  • Snowdonia, Gwynedd: within the Snowdon Caldera, massive chalcopyrite is a major component of the lodes that developed during underground fluid circulation and fracturing related to the evolution of this large volcanic caldera in Mid-Ordovician times (Reedman et al., 1985). Associated sulphide minerals include sphalerite, pyrite, pyrrhotite, arsenopyrite and galena. The most important mines were, from north to south, Llanberis, Britannia, Lliwedd, Drws-y-coed, Simdde Dyllaun and Sygun, with a large number of smaller mines and trial workings situated in the same area (Bick, 1982).
  • South Wales: chalcopyrite is widespread across this area in a variety of settings. It occurs in veins cutting Lower Palaeozoic rocks, with quartz and carbonates at the Ramsey Copper Mine near St. David's and with tetrahedrite, galena and bournonite at the St Elvis Mine, near Solva (Mason & Bevins, 2002), both in the extreme west of the area. Further east it is found in veins cutting Carboniferous Limestone at Mynydd-y-Gareg, near Kidwelly (Strahan et al, 1909), while it is also present as a minor component of Mississippi Valley-type veins present in the Carboniferous Limestone outcrop in the Cardiff district, for example at Machen Quarry and in the Llantrisant district. Chalcopyrite is also present within the ironstone nodule/sandstone joint assemblages of the South Wales Coalfield, where it forms sharp, euhedral crystals to a few millimetres across in association with millerite, siegenite, galena, sphalerite, quartz, siderite and ankerite (Firth, 1971). Good specimens have been recovered from coal-tips during reclamation projects and also from modern opencast coal-workings, such as those at Nant Helen near Ystradgynlais in West Glamorgan.

There are no key localities for this specimen.

References:

  1. Allen, P.M. & Easterbrook, G.D., 1978. Mineralised breccia pipe and other intrusion breccias in the Harlech Dome, N. Wales. Transactions of the Institution of Mining and Metallurgy (Section B; Applied earth science), 87, B157-B161.
  2. Bevins, R.E. & Mason, J.S., 1997. Welsh metallophyte and metallogenic evaluation project: Results of a minesite survey of Dyfed and Powys. CCW Contract Science Report No. 156. National Museums & Galleries of Wales.
  3. Bevins, R.E. & Mason, J.S., 1999. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Clwyd. National Museums & Galleries of Wales, Cardiff.
  4. Bick, D.E., 1982. The Old Copper Mines of Snowdonia. Second Edition. Pound House, Newent.
  5. Firth, J.N.M., 1971. The Mineralogy of the South Wales Coalfield. Unpublished Ph.D. thesis, University of Bristol.
  6. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
  7. Hall, G.W., 1990. The Gold Mines of Merioneth. 2nd ed. 99pp. Griffin Publications, Kington.
  8. Ixer, R.A. & Davies, J., 1996. Mineralisation at the Great Orme Copper Mines, Llandudno, North Wales. U.K. Journal of Mines and Minerals, 17, 7-14.
  9. Jones, O.T., 1922. Lead and zinc. The mining district of North Cardiganshire and West Montgomeryshire. Memoirs of the Geological Survey. Special Report of the Mineral Resources of Great Britain, 20.
  10. 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.
  11. Mason, J.S. & Bevins, R.E., 2002. St Elvis Mine, Solva, Pembrokeshire: Another Elizabethan tetrahedrite occurrence? British Mining 71, 5-12, Northern Mines Research Society.
  12. 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.
  13. 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.
  14. 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.
  15. Rice, R. & Sharp, G.J., 1976. Copper mineralization in the forest of Coed-y-Brenin, North Wales. Transactions of the Institution of Mining and Metallurgy, (Section B: Applied earth science), 85, B1-B13
  16. Strahan, A. Cantrill, T.C., Dixon, E.E.L. & Thomas, H.H., 1909. The geology of the South Wales Coalfield. Part X. The geology around Carmarthen. Memoirs of the Geological Survey of England and Wales. Explanation of Sheet 229.

There are no references for this specimen.