De Lank Quarries
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Condition (Natural England)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| SX101753 | — | Favourable | 22.0 | 2013-02-28 |
Geology & landscape
Geological Period: Carboniferous · Rock Type: Granite
Landscape processes: Volcanic / Igneous
Description
De Lank Quarries SSSI Description A Geological Conservation Review site. This site provides a superb example of Cornubian coarse biotite granite of small megacryst type (S-type), within the Permo-Carboniferous Bodmin Moor intrusion. The granite has a strong, approximately north-south trending sub-vertical tectonic foliation, emphasised by orthoclase megacrysts and irregular bands of strained quartz. This site provides one of the strongest examples of this texture and unique, unambiguous evidence of a deformation origin. The deep quarries also clearly demonstrate that the sub-horizontal jointing within near-surface granite exposures disappears with depth, and are not therefore an original cooling feature. Other important features of this site include a major occurrence of fresh, fine-grained megacrystic biotite granite and three substantial outcrops of late-stage granite porphyry (‘elvan’) dykes. All these features are of key importance in deciphering the complex intrusive history of the Cornubian batholith during the late Palaeozoic.