Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Silver antimony sulphide
Chemical Formula: Ag3SbS3
Method(s) of Verification: Tyddyn Gwladys Mine - EMPA (Gilbey, 1968).
- Hydrothermal: mesothermal polymetallic veins
Introduction: pyrargyrite is typically found in low to medium temperature hydrothermal veins, where it may be associated with tetrahedrite, galena, sphalerite and other silver sulphosalts. It also occurs in the rare but sometimes economically important 'five-metals association', where it is accompanied by other Ag minerals plus those of Ni, Co, As and Bi. Pyrargyrite is one of the so-called Ruby Silvers - a group of silver minerals that are red when fresh (especially the arsenic analogue of pyrargyrite, proustite - Ag3AsS3) but which characteristically tarnish black on exposure to bright light.
Occurrence in Wales: the Tyddyn Gwladys mine, which worked mesothermal veins in the Dolgellau Gold-belt, was long known for its localized but high-grade silver mineralization and an interesting account is presented by Hall (1990). Discrete silver minerals were known to occur in the lodes as long ago as the late 19th Century and using ore petrography and electron microprobe analyses, Gilbey (1968) finally established their identity and composition, with pyrargyrite being among the species present.
- Tyddyn Gwladys Mine, Ganllwyd, Dolgellau, Gwynedd: pyrargyrite occurs locally in association (in order of abundance) with argentian tetrahedrite, electrum and polybasite, as intergrowths included in galena and also associated with chalcopyrite and sphalerite (Gilbey, 1968; Mason et al., 2002). The latter authors suggested the possibility that the Ag-Au-Sb-Pb rich mineralization occurring locally at this mine might be a variant of the high-grade Au-Ag-Bi-Te-Pb mineralization that occurs in gold-bearing oreshoots in the area.
- 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 Unpublished Ph.D thesis, University of London, UK.
- Hall, G.W., 1990. The Gold Mines of Merioneth. 2nd ed. 99pp. Griffin Publications, Kington.
- 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.