Altaite

Crystal System: Cubic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: Lead telluride
Chemical Formula: PbTe
Method(s) of Verification: Clogau Mine - EMPA (Gilbey, 1968).

Chemical Group:

  • Sulphides

Geological Context:

  • Hydrothermal: mesothermal polymetallic veins
Introduction: altaite occurs in hydrothermal veins and is commonly associated with gold, galena and other telluride minerals.
Occurrence in Wales: altaite was first reported from Wales at 'Bontddu, entre Dolgelley et Barmouth, Galles du Nord' (Des Cloizeaux, 1893). The nearest significant mine to Bontddu is the Clogau Gold Mine, where both Gilbey (1968) and Naden (1988) have subsequently confirmed the presence of microscopic altaite, in association with other telluride minerals, in polished section. The interesting point about the 1893 report is that it dates from a time when ore microscopy was at a relatively early stage of its development. The difficulty in studying very fine-grained material at that time would therefore suggest that the occurrence reported by Des Cloizeaux was richer/coarser grained than those that have been found since.

Key Localities:

  • Clogau Mine, Bontddu, Gwynedd: the most detailed description is that of Gilbey (1968) who observed altaite in polished section. It forms granular to subrounded inclusions in tellurobismuthite and is associated with inclusions of hessite, either as a rim or a dual inclusion. Although no fully quantitative analyses are available, Gilbey (1968) stated that his analysis gave a 'formula equivalent to lead telluride'.

There are no key localities for this specimen.

References:

  1. Cloizeaux, A.L. Des., 1893. Manuel de Minéralogie, II. Paris, 305-306.
  2. 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 Unpublished Ph.D thesis, University of London, UK.
  3. Naden, J., 1988. Gold mineralisation in the Caledonides of the British Isles with reference to the Dolgellau Gold Belt and the Southern Uplands of Scotland. Unpublished Ph.D thesis, University of Aston, UK.

There are no references for this specimen.