Area: 113.5 hectares.
In Cornwall Area of Outstanding Natural Beauty and Heritage Coast.
The site includes the GCR site of Cligga Head Mine.
Description and Reasons for Notification:
Cligga Head is a coastal site with species rich maritime heathland and grassland. The cliffs and adjacent mine workings are of outstanding geological interest exposing greisened granite and rare minerals.
The site extends for about 2.5 km along the North Cornwall coast from Perranporth to Trevaunance Cove near St Agnes. The exposed north-west facing cliffs have a bevelled profile with steep slopes rising to 91 metres A.O.D., then a vertical cliff of 25 to 35 metre height. Most of the area is underlain by Devonian slates of the Ladock Beds, which are metamorphosed throughout the northern half of the site, due to the intrusions of the granite boss exposed at Cligga Head.
This site, which is of international geological repute, shows a remarkable example of extensive alteration of a granite of Permo-Carboniferous age by a range of secondary processes. Flat lying joints, formed as the granite cooled, are folded into an antiform and synform. These deformed joint structures are unique in the granites of southwest England, and together with two steeply dipping channelways largely determined the distribution of the effects of later alteration processes such as greisening (modification of granite to a quartz-mica rock often adjacent to veins), higher and lower tempeature mineralisation and kaolinisation.
The site also shows an extremely fine example of a vein swarm resulting from the fracturing of a granite cusp. The quarry above the mine exposes granite, greisenized along joints in bands up to 0.5 m in width. The greisen contains cassiterite, wolframite, topaz, tourmaline and copper minerals. The mine workings are exposed in the cliff face and large areas of dumps yield interesting mineral specimens. Marine erosion of the veins ensures a supply of vein material on the beach below the cliffs. Rarer minerals include isostannite, molybdenite and euclase. The secondary alteration produce of stannite, varlamoffite was recorded here for the first time in Britain. Other secondary minerals often as fine specimens, are scorodite, olivinite and pharmacosiderite. The mineralisation is representative of the lower part of the tin zone but the mine was worked for tungsten rather than tin. Soils are well drained and in many areas are extremely toxic due to mine waste deposits rich in toxic metals.
Most of the site is covered in maritime heath, with occasional patches of maritime grassland. Bracken and scrub occur only in small clumps. Much of the area around Cligga Head has been disturbed by mining in the past but this is being recolonised by ling Calluna vulgaris. Western gorse, Ulex gallii, and bell heather Erica cinerea occur elsewhere, forming extensive areas of maritime heathland on the less disturbed southern area. Associated herbs include common dog violet Viola riviniana, wild carrot Daucus carota, tormentil Potentilla erecta, the rare plant species, hairy greenweed Genista pilosa, and the local pale heath violet Viola lactea. Another rare plant species, Cornish eyebright Euphrasia vigursii has also been reorded. Mountain everlasting Antennaria dioica, which is normally restricted to northern England and Scotland, and soft leaved sedge Carex montana, which is very local nationally, also occur here. On sections of the north facing cliff, there are abundant cowslips Primula veris.
Maritime grassland is restricted to the cliff edges. Typical species include red fescue Festuca rubra, thrift Armeria maritima, spring squill Scilla verna, kidney vetch Anthyllis vulneraria, and burnet rose Rosa pimpinellifolia. Portland spurge Euophorbia portlandica, a species restricted to the southwest coast, is found in the northern section, as is rock sea lavender Limonium binervosum.
The area is moderately rich in bryophyte species. Tortella tortuosa is a moss rare in the south of Britain and there are two liverwort species of particular note; Fossombronia husnotii var. anglica, which is local in Cornwall and nationally restricted to the southwest and south Wales, and Jungermannia pumilum which is rare in west Cornwall.
Cligga Head is also an important site for lepidoptera; some 88 moth species and four butterfly species have been recorded here including grayling Hipparchia semele, and the very local silver-studded blue Plebejus argus.