Earth Science Conservation Review
| Curraghinalt - site of local interest | Tyrone |
| Site Type: | Stream section |
| Site Status: | local interest |
| Council area: | Omagh District Council |
| Grid Reference: | H571865 |
| Google maps: | 54.72371,-7.1138 |
| Rocks | |
|---|---|
| Rock Age: | Carboniferous, Ordovician, Precambrian |
| Rock Type: | Psammite |
| Interest | |
| Minerals: | Gold, Pyrite, Quartz, Electrum |
| Other interest: | hydrothermal vein |
Description:
The site is located approximately 150m upstream of the Attys Bridge in the Curraghinalt Burn, which forms the boundary between Attagh and Curraghinalt Townlands 8km east of Gortin. The vein is exposed in the bed of the stream and samples can be obtained of coarse-grained pyritic quartz vein material. Gold is not generally visible in hand specimen. A bulk sample of vein material was removed from the east flank of the stream valley but the vein is no longer exposed in the pit, which has grassed over.
Evidence from mineralogical studies and cathodoluminescence microscopy (Earls et al., 1996; Parnell et al., 2000; Wilkinson et al., 1999) indicates that several stages of cross-cutting quartz (Q2-Q4) were introduced during brittle deformation following the formation of early veining (Q1) due to defluidization during ductile deformation and metamorphism of the Dalradian host rocks. Volumetrically minor, early paragenetic (Q2) electrum is encapsulated within pyrite. However, most electrum occurs along pyrite crystal boundaries, or is related to cross-cutting fractures that also contain baryte, chalcopyrite, tetrahedrite, quartz and dolomite, that were formed during a secondary mineralising event (Q4). In one sample which was the subject of detailed study, the syn-pyrite and post-pyrite electrum have a different chemistry: earlier electrum has a lower silver content than that in cross-cutting veinlets. Volumetrically minor amounts of gold-bearing tellurides containing up to 5.9 at% Au were also observed as micron-scale crystals enclosed within pyrite. The most common is bismuth telluride, less common are gold-silver tellurides including hessite [Ag,Au]2Te, mercury telluride and the lead telluride, altaite [PbTe].
Evidence from mineralogical studies and cathodoluminescence microscopy (Earls et al., 1996; Parnell et al., 2000; Wilkinson et al., 1999) indicates that several stages of cross-cutting quartz (Q2-Q4) were introduced during brittle deformation following the formation of early veining (Q1) due to defluidization during ductile deformation and metamorphism of the Dalradian host rocks. Volumetrically minor, early paragenetic (Q2) electrum is encapsulated within pyrite. However, most electrum occurs along pyrite crystal boundaries, or is related to cross-cutting fractures that also contain baryte, chalcopyrite, tetrahedrite, quartz and dolomite, that were formed during a secondary mineralising event (Q4). In one sample which was the subject of detailed study, the syn-pyrite and post-pyrite electrum have a different chemistry: earlier electrum has a lower silver content than that in cross-cutting veinlets. Volumetrically minor amounts of gold-bearing tellurides containing up to 5.9 at% Au were also observed as micron-scale crystals enclosed within pyrite. The most common is bismuth telluride, less common are gold-silver tellurides including hessite [Ag,Au]2Te, mercury telluride and the lead telluride, altaite [PbTe].
| Enlander, I., Dempster, M. & Doughty, P., 2024. Curraghinalt - site of local interest, County Tyrone, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=722. Accessed on 2024-12-26 |
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