Granite-related mineralization.
Cligga Head granite is intruded in Devonian metasediments.
The granite is cut by greisens-bordered NE vein-system.
The greisens are cored by Sn-W-As-quartz veins.
Sulfide mineralization occurs in fractures crosscutting Sn-W-As-quartz veins.
The granite is rimmed by a tourmalinite alteration aureole.
Hydrothermal activity : 350-400 °C, 0.7 (boiling)-1.7 kb.
Na-K-Fe-Ca chloride brines rich in B, F, SO4 (degassing of magmatic volatiles).
This locality includes
- the Cligga Mine,
- the exposure of the greissen-sheet vein stockworks (another SSSI, so hammers in bags!), located just below the 1940's mine works on the top of the cliff, and
- the beach, with numerous vein outcrops and scattered material from the mine and its dumps
The beach at the entrance to the mine yields arsenopyrite, wolframite, and cassiterite without having to look too hard. More cassiterites are easily found on the beach around the cliff past the mine entrance, which can be accessed at low tide.
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UK OS Grid Reference: SW737536
Map Reference: 50°20'17"N , 5°10'50"W
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