Cubanite

Crystal System: Cubic,Orthorhombic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Copper iron sulphide
Chemical Formula: CuFe2S3
Method(s) of Verification: Cefndeuddwr Mine & Hendreforion Mine - SEM-EDX (National Museum of Wales).

Chemical Group:

  • Sulphides

Geological Context:

  • 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.

Key Localities:

  • 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).

There are no key localities for this specimen.

References:

  1. 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 Unpublished Ph.D thesis, University of London, UK.
  2. 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.

There are no references for this specimen.