Wolframite

Crystal System: Monoclinic
Status of Occurrence: Unconfirmed Occurrence
Distribution: Rare
Chemical Composition: Iron manganese tungstate
Chemical Formula: (Fe,Mn)WO4
Method(s) of Verification: both localities insufficiently verified, the presence of tungsten identification by EMPA and XRF.

Chemical Group:

  • Sulphites, Chromates, Molybdates & Tungstates

Geological Context:

  • Hydrothermal: mesothermal polymetallic veins
Introduction: wolframite forms typically in (i) high to medium temperature quartz-rich veins in greisen, or in pegmatites associated with granitic intrusive rocks; (ii) in high-temperature hydrothermal ('hypothermal') veins associated with cassiterite, arsenopyrite, apatite, tourmaline, topaz, fluorite, specular hematite, molybdenite, and bismuth; (iii) in mesothermal veins, with cassiterite and sulphides, scheelite, bismuthinite, and siderite.
Occurrence in Wales: Colman and Appleby (1991) tentatively reported wolframite (based on the presence of tungsten during electron microprobe analysis), occurring as small grains associated with cassiterite as inclusions, in magnetite within breccia from Shadow Gully. High levels of tungsten were also proved during XRF scans of milled samples of quartz-magnetite veins, derived from Cwm Tregalan. Bevins & Mason (1998), however, describe scheelite developed between magnetite grains within the Shadow Gully breccia. The presence of scheelite explains the high levels of tungsten recorded by Colman & Appleby (1991) suggesting, that wolframite may not actually be present.

Key Localities:

  • Cwm Tregalan, Snowdon, Gwynedd: high levels of tungsten was detected in milled samples of quartz-magnetite veins from Cwm Tregalan within the Snowdon caldera (Colman & Appleby, 1991).
  • Shadow Gully, Snowdon, Gwynedd: a tungsten-bearing mineral is present as inclusions in magnetite breccia exposed in Shadow Gully within the Snowdon caldera (Colman & Appleby, 1991).

References:

  1. Bevins, R.E. & Mason, J.S., 1998. Welsh Metallophyte and metallogenic evaluation project: Results of a Minesite Survey of Gwynedd. National Museums of Wales, Cardiff.
  2. Colman, T.B. & Appleby, A.-K., 1991. Volcanogenic quartz-magnetite-hematite veins, Snowdon, North Wales. Mineralogical Magazine, 55, 257-262.