A super day out yesterday, looking at our outstanding local Cornish geology, with Camborne School of Mines, University of Exeter MSc Exploration and Mining Geology students.
Rinsey Cove to start with, looking at evidence for three principal episodes of hydrothermal fluid flow and vein development within the contact metamorphosed (andalusite-cordierite-biotite) Mylor Slate Formation: (1) regional metamorphic quartz veins (Carboniferous, developed during Variscan continent-continent collision), (2) magmatic-hydrothermal quartz-tourmaline and quartz-chlorite-sulphide veins, exhibiting local cockade texture (Early Permian, developed during N-S regional post-Variscan extension and batholith construction) - worked for Cu/Sn in 1860s by Wheal Prosper (engine house in first image), and (3) post-granite epithermal ‘cross-course’ veins (Triassic, related to E-W extension and migration of brines sourced from Permo-Triassic ‘red-bed’ sedimentary successions into the pre-Permian basement).
The immediately underling Tregonning Granite is one of three principal surface expressions of the G5 topaz granites, that are the most Li-enriched in SW England. They exhibit aplite-pegmatite and complex textures in their roof zones - dislayed superbly in boulders. These typically have higher Li content than the host granites.
We then moved to Porthleven and saw some good examples of quartz-siderite (hematite)-galena-sphalerite-chacopyrite epithermal ‘cross-course’ vein mineralisation derived from NNW-SSE-striking lodes worked by Wheal Penrose and Wheal Rose. The day ended with a brief look at folds and foliations developed in the Portscatho Formation during Variscan thrusting and post-Variscan extension and thrust fault reactivation. And a little on Quaternary climate changes, periglaciation, changing sea-levels and Cretaceous chert on Cornish beaches.
#Cornwall #tectonics #Variscan #CornubianBatholith #mineralisation
#tin #copper #lead #zinc #lithium #resources
Graduate School of Environment and Sustainability, University of Exeter
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