Gersdorffite

Crystal System: Cubic
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Nickel arsenic sulphide
Chemical Formula: NiAsS
Method(s) of Verification: Great Orme Mines - EMPA (P. Eakin, unpublished data); Gwaithyrafon Mine - EMPA (Rust & Mason, 1994).

Chemical Group:

  • Sulphides

Geological Context:

  • Hydrothermal: Mississippi Valley Type veins
  • Hydrothermal: mesothermal polymetallic veins
Introduction: gersdorffite occurs typically, with other sulpharsenide minerals, in microscopic inclusion-forming assemblages within commoner sulphides such as galena in hydrothermal ore deposits. Because of its minute grain size, gersdorffite requires electron microprobe analysis for proper confirmation.
Occurrence in Wales: records of gersdorffite in Wales are few, although there are many cases of sulpharsenide inclusion assemblages that have yet to be analytically investigated. Examples include, among others, the mineralization at Dolyhir Quarry and the Llangynog Orefield in Central Wales. However it has been identified at one locality in Central Wales and at the Great Orme near Llandudno.

Key Localities:

  • Great Orme Copper Mines, Llandudno, Gwynedd: gersdorffite has been identified as microscopic grains coating fractures within uraniferous hydrocarbon which occurs intermittently within this ore deposit (P. Eakin, unpublished data).
  • Gwaith-yr-Afon Mine, Goginan, Ceredigion: this locality is noted for supergene arsenate minerals and the search for the primary source of arsenic resulted in the identification, by electron microprobe analysis, of small gersdorffite inclusions in galena (Rust & Mason, 1994).

References:

  1. Rust, S.A. & Mason, J.S., 1994. An unusual occurrence of arsenate minerals at Gwaith-yr-Afon mine, Dyfed, Wales. Journal of the Russell Society, 5(2), 109-113.