Tregargus Quarries

Site of Special Scientific Interest · 50.3507, -4.8843

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Cornwall County

Condition (Natural England)

Unfavourable No Change (1)
UnitFeatureConditionArea (ha)Assessed
SW949540 — Unfavourable No Change 1.62 2011-06-22

Geology & landscape

Geological Period: Carboniferous · Rock Type: Granite

Landscape processes: Volcanic / Igneous

Description

Tregargus Quarries SSSI Description These quarries provide excellent exposures of two late-magmatic varieties of the varied St. Austell granite mass (of Permo-Carboniferous age). Fluorite granite predominates, but this is accompanied by irregular patches of non-megacrystic lithium-mica granite. The site is significant in illustrating that the contacts between the two rock-types are transitional and non-intrusive in nature and they may be accounted for by metasomatic over-printing of an original biotite granite by a lithium-rich fluid. The biotite was replaced by a lithium mica while elsewhere high fluorine contents resulted in the crystallisation of fluorite.