Crystal System: Cubic,Orthorhombic
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Copper iron sulphide
Chemical Formula: CuFe2S3
Method(s) of Verification: Cefndeuddwr Mine & Hendreforion Mine - SEM-EDX (National Museum of Wales).
- Hydrothermal: mesothermal polymetallic veins
SEM photomicrograph of cubanite showing sub-parallel lamellae in chalcopyrite from Cefndeuddwr Mine in the Dolgellau Gold-belt. Scale bar 40 microns. © National Museum of Wales.
Introduction: cubanite is a relatively high-temperature mineral often found in magmatic copper-nickel (Cu-Ni) sulphide deposits. It also occurs in medium to high-temperature hydrothermal veins, where it is typically seen as an exsolved phase in chalcopyrite. Cubanite is difficult to identify in polished section, especially in plane polarized light using standard lenses; under oil immersion and crossed polars it is easier to recognise. The paragenetic association with chalcopyrite and pyrrhotite is a useful diagnostic aid.
Occurrence in Wales: the first record of cubanite from Wales was by Gilbey (1968), who identified isometric cubanite inclusions in chalcopyrite in a polished section of sulphide-bearing material from a mine in the Dolgellau Gold-belt. More recently, work at the National Museum of Wales on Gilbey's samples has resulted in the confirmation of cubanite from a second mine in the same area (Mason et al., 2002). The host assemblage (pyrrhotite and chalcopyrite with sphalerite exsolution bodies) is widespread across the Gold-belt and it is likely that cubanite is of a wider distribution than has so far been recognised.
- Cefndeuddwr Mine, Ganllwyd, Gwynedd: as rather subtle, orientated lamellar intergrowths with chalcopyrite (Mason et al., 2002).
- Hendreforion Mine, Bontddu, Gwynedd: as inclusions in chalcopyrite (Gilbey, 1968).
- Gilbey, J.W., 1968. The mineralogy, paragenesis and structure of the ores of the Dolgellau Gold Belt, Merionethshire, and associated wall rock alteration. Unpublished Ph.D thesis, University of London, UK.
- 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.