County Geology Site Criteria for Cornwall and the Isles of Scilly

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CORNWALL RIGS GROUPCOUNTY GEOLOGY SITE SUMMARY FORMSite DetailsSite name: Venton Cove Site number: P/2National Grid reference SW 527301 OS sheet no: SW 53 BGS sheet no: 351District Council(s)PenwithDate approved: 24/09/1992 Date notified: 10/02/1993, amended 27/4/2007Site ownership: Duchy of Cornwall Mineral rights ownership: Duchy of CornwallProposer: C S ExleyDate of Initial Field Visit: 18/7/1989Site AccessAccess to the site:From Turnpike Road, Marazion, follow long distance path down to cliff edge, the site is on the foreshore 250m to thesouth.Access permission needed from:CRoW Act Access RightThe site is suitable for:Nonelarge parties and frequent visits.Site DescriptionSummary Description:Pneumatolytic Breccia Intrusion, intersected by an elvan dyke and a cross-cutting epithermal quartz vein, intruded into Killas. Raised beach and’head’ deposits in the cliff.Dimensions of area of interest: 150m x 100mType of Exposure (Earth Science Conservation Classification, revised 2004)Exposure or Extensive Sites:Integrity Sites:Finite Sites:Geological Interest categoriesMain site interest:Additional site interest(s):Conservation Designations -SAC Name:SSSI Name:GCR Block:Coastal cliffs and foreshore.Finite mineral, fossil or other geological.Igneous rocksCounty Wildlife Site Name(s): Mount’s Bay P3.4Stratigraphy/Sedimentary rocks/GeomorphologyDetails of any ecological interest: Intertidal communities.County Wildlife Site/Area of Outstanding Natural BeautyWorld Heritage Site Area/Mining DistrictPublished references to the site:Goode, A.J.J. & Taylor, R.T.1980. Intrusive and Pneumatolytic Breccias in South-West England. Institute of Geological Sciences, ReportCornwall RIGS Group County Geology Site Summary FormP/2 Venton Cove11 December 2007
80/2. Bromley, A.V.1989. Field Guide to the Cornubian Orefield. Sixth International Symposium on Wayer-Rock Interaction, InternationalAssociation of Geochemistry and Cosmochemistry, Malvern. Camborne School of Mines.Site SignificanceScientific importance:Educational value:The site is considered to be of regional scientific importanceThe site is of educational valueDetails of Educational InterestRock types; cross-cutting relationshipsEducational Groups most likely to benefit are: Secondary, Adult & Continuing and Higher Ed.Historical importance: The site is not known to have any important historical associations.Aesthetic Appeal:Details of any Economic AssociationsThe site forms a key part of an attractive or evocative landscape.Full description of the site and its significance:The focus of interest is a breccia dyke, about 3m wide, intruded into killas. It lies on the east (footwall) side of an elvan dyke which strikesNE/SW and widens from 3-4m, at its seaward end to 15-20m near the low cliff. The elvan intersects the breccia and has a 0.5m selvedgecontaining breccia fragments along its footwall. Fragments in the breccia are of Mylor Slate Formation metasediment, greenstone and a smallamount of granite, set in a tourmaline matrix. There are many breccias of this type in Cornwall, some intrude granite eg. Wheal Remfrey, StAustell and most are associated with elvans and mineral veins. This suggests they are just post-granite in age, their constituent fragmentsinclude several rock types, the proportion of granite depending on the proximity to a granite intrusion, and vary both in size and angularity.The matrix consists of fine rock and mineral fragments in which quartz and tourmaline predominate and in which there has usually beenextensive tourmalinisation and chloritisation. Their origin lies in the build-up of pressure from volatiles (chiefly water and boron) beneath agranite carapace at the end of magmatic crystallisation. The release of pressure from jointing or fracturing was followed by the implosion ofsurrounding rock into the cavities, creating the breccia. The exposure of the hydrothermal breccia is mainly below the high water mark andcan be obscured by shingle. Also exposed is a cross-cutting NW – SE striking epithermal quartz vein, 2-3m in width, probably displacing theelvan dyke. At SW5280 3017, some 25m SE of the dyke, there is an excellent exposure of the same quartz vein exhibiting both a bandedcockscomb appearance. In the cliff, a raised beach of pea gravels is exposed, overlain by periglacial ‘head’.Site Management and Monitoring SummaryKey issues/potentially damaging activities:None identifiedManagement required:NoneDetails of management carried out:Date of last visit to the site: January 2007Surveyor: Simon CammDate site was last photographed : January 2007Cornwall RIGS Group County Geology Site Summary FormP/2 Venton Cove11 December 2007
Page 1 and 2: HeadingCounty Geology SiteCriteria
Page 3 and 4: COUNTY GEOLOGY SITE CRITERIA FORCOR
Page 5 and 6: 2. CONTEXT AND BACKGROUND2.1 The Ge
Page 7 and 8: 3. COUNTY GEOLOGY SITE SELECTIONThe
Page 9 and 10: D Geological site assessment will b
Page 11 and 12: 4. The Local Sites Partnership will
Page 13 and 14: 2. Educational valueThe criteria fo
Page 15 and 16: BIBLIOGRAPHYBristow, C.M. 1996. Cor
Page 17 and 18: LIST OF APPROVED COUNTY GEOLOGY SIT
Page 19 and 20: SITE NAME NO. GRID REF. SUMMARY OF
Page 21 and 22: APPENDIX 2The Geological Conservati
Page 23: APPENDIX 3Example of a County Geolo
Page 27 and 28: 01/07Cliff section showing raised b
Page 29 and 30: Cornwall RIGS Group County Geology
Page 31 and 32: Tick when Process CompleteProtocol
Page 33 and 34: Site Contraction/DeletionDetails of
Page 36: Heading

County Geology Site Criteria for Cornwall and the Isles of Scilly

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