Petzite

Crystal System: Cubic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Silver gold telluride
Chemical Formula: Ag3AuTe2
Method(s) of Verification: Deepford Brook: electron-microprobe spot analyses on individual gold grains carried out by the British Geological Survey (BGS).

Chemical Group:

  • Sulphides

Geological Context:

  • Sedimentary: allogenic (detrital)
Introduction: a rare silver-gold telluride which occurs as minute inclusions within gold.
Occurrence in Wales: inclusions of coloradoite, petzite and a Cu telluride are reported by Norton et al. (2000) in gold grains from a sample taken from just above the confluence of the Deepford Brook with the Afon Syfni, near Clarbeston in Pembrokeshire. Prior to this, petzite was tentatively identified as an 8 ┬Ám diameter grain associated with possible calaverite included within alluvial gold from the Afon Wen, near Dolgellau, Gwynedd (Leake et al., 1993).

Key Localities:

  • Deepford Brook, Clarbeston, Pembrokeshire: a sample (PW114) taken from just above the confluence of the Deepford Brook with the Afon Syfni was found to contain a well-defined type of gold with telluride inclusions (Norton et al., 2000). The tellurides coloradoite, petzite and a Cu telluride were found to be present, together with pyrite and pyrrhotite.

References:

  1. Leake, R.C., Bland, D.J. and Cooper, C., 1993.. Source characterization of alluvial gold from mineral inclusions and internal compositional variation. Transactions of the Institution of Mining and Metallurgy. B102, 65-82.
  2. Norton, G.E., Cooper, D.C., Davies, J.R. and Cornwell, J.D., 2000. Evidence for gold mineralisation in the Lower Palaeozoic and Precambrian rocks of south-west Wales. BGS Research Report RR/00/10. DTI Minerals Programme Publication No. 5.