Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Chemical Composition: Silver copper antimony sulphide
Chemical Formula: (Ag,Cu)16Sb2S11
Method(s) of Verification: Tyddyn Gwladys Mine - appears to be by EMPA (Gilbey, 1968).
- Hydrothermal: mesothermal polymetallic veins
Introduction: polybasite occurs with other silver sulphosalts and base-metal sulphides in low to medium-temperature hydrothermal mineral veins.
Occurrence in Wales: Gilbey (1968) identified polybasite, associated with pyrargyrite, from Tyddyn Gwladys Mine in the Dolgellau Gold-belt. The locality is historically known for its high-grade silver ores (Hall, 1990). Mason et al. (2002) suggested the possibility that the Ag-Au-Sb-Pb rich mineralization occurring at this mine might be a variant of the high-grade Au-Ag-Bi-Te-Pb mineralization that occurs very locally in gold-bearing oreshoots in the area.
- Tyddyn Gwladys Mine, Ganllwyd, Dolgellau, Gwynedd: identified in polished sections of sulphide ores by Gilbey (1968), occurring as part of an Ag-rich inclusion assemblage occurring locally in galena and including pyrargyrite, argentian tetrahedrite and electrum. Polybasite was stated to be much rarer than pyrargyrite.
- 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 Unpublished Ph.D thesis, University of London, UK.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.