St. Mewan Beacon
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Condition (Natural England)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| SW985534 | — | Unfavourable Declining | 0.68 | 2023-01-17 |
Geology & landscape
Mining / Industrial: Quarry · Geological Period: Carboniferous · Rock Type: Granite
Landscape processes: Volcanic / Igneous
Description
St. Mewan Beacon SSSI Description This site comprises a small quarry and tor exposures in quartz-topaz-tourmaline rocks at the southern edge of the Permo-Carboniferous St. Austell granite. Modal variation has resulted in the rocks being banded in places and tourmaline-topaz and quartz-rich varieties are present. Although close to the margin of the granite the rocks do not represent a sheeted roof complex, such as that seen at Porthcew, as their composition is too refractory to have separated directly from a magma. It is rather thought that the St. Mewan rocks represent the crystallised silica-rich fraction of a hydrothermal saline ore-bearing fluid, which became entrapped beneath the impermeable pelitic roof rock at St. Mewan. This site is of great scientific interest as it documents an important evolutionary stage between late-stage granite processes and later mineralising events in south-west England.