Geology of Exeter and its environs

A 225 km² area around Exeter, described in this report, extends from the villages of Brampford Speke and Whimple in the north to Aylesbeare, Exminster and Woodbury in the south. It is underlain by Carboniferous, Permian, and Triassic solid formations and by a variety of Quaternary superficial deposits. The Namurian Crackington Formation comprises mainly tightly folded shales with subordinate sandstone interbeds. The Permian rocks consist of a lower, predominantly: breccia, sequence (Whipton Formation, Teignmouth Breccia, Monkerton Member) that thins and disappears northwards against a possibly fault-controlled ridge of Crackington Formation; the breccias are overlain by sandstones and mudstones (Dawlish Sandstone and Aylesbeare Mudstone). Volcanic rocks occur at the base of the Permian sequence and possibly within the Dawlish Sandstone. The latter splits into five alternating sandstone and mudstone members when traced northwards from Exeter into the Crediton Trough (an area of thick Permian sediments). The Aylesbeare Mudstone is divisible south of Aylesbeare into two members, the lower containing impersistent sandstones. It is overlain by the basal Triassic gravels (Budleigh Salterton Pebble Beds) which are in turn succeeded by the Otter Sandstone

Baseline geochemistry of Devonian low-grade metasedimentary rocks in Cornwall: preliminary data and environmental significance.

Geochemical baseline data provide information on the state of the environment before modification by mining and other anthropogenic activities. A summary of the analyses of 41 elements on 100 samples from Devonian metasedimentary rocks away from areas of mineralization and granite intrusions in Cornwall are presented. The data show a remarkable consistency. Differences in major elements can be related largely to changes in mineral proportion expected from grain size variations within the sedimentary rocks. The trace element data indicate that similar types of sediment accumulated in the Gramscatho, Looe and Trevone basins and that subsequent metamorphism has not significantly re-distributed elements. Compared with an average UK Lower Palaeozoic shale and the North American Shale Composite, the Devonian metasedimentary rocks of Cornwall appear to be marginally depleted in many trace elements. Values for As, Ni and Cr frequently exceed published soil guideline values, especially in mudstones, which brings into question the issue of the identification of land, which is considered to be polluted

APPLIED GEOLOGICAL MAPPING SOUTHAMPTON AREA: area covered by 1:50,000 Geological sheet No. 315 (Southampton) OS 1:10,000 sheets SU31 and 41, and parts of SU20, 21, 22, 30, 32, 40, 42, 50, 51 and 52

This study was commissioned by the Department of the Environment to develop and apply techniques of applied geological mapping for the purposes of land-use planning and development. It covers the area of the British Geological Survey (BGS) 1:50,000 geological map of Southampton. The study involved the computer manipulation of existing geological, geotechnical, hydrogeological and mineral resource data. The objectives were to develop the methodology, and to provide an archive of information, a set of applied geological maps, and descriptive reports in a form appropriate to all potential users. The computer is a powerful tool for bringing together spatially referenced information from many sources. There was collaboration with the Ordnance Survey and also with the Soil Survey of England and Wales who have been commissioned to undertake a study in the same area

Mineral resource information in support of national, regional and local planning : Devon (comprising Devon, Plymouth, Torbay, Dartmoor National Park and part of Exmoor National Park)

This report is one of a series prepared by the British Geological Survey for various administrative areas in England for the Office of the Deputy Prime Minister’s research project Mineral Resource Information in Support of National, Regional and Local Planning. The accompanying maps relate to the county of Devon and delineates the mineral resources of current, or potential, economic interest in the area and the sites where minerals are or have been worked. It also relates these to national planning designations, which may represent constraints on the extraction of minerals. Three major elements of information are presented: • the geological distribution and importance of mineral resources; • the extent of mineral planning permissions and the location of current mineral workings; and • the extent of selected, nationally-designated planning constraints. This wide range of information, much of which is scattered and not always available in a consistent and convenient form, is presented on two digitally-generated summary map on the scale of 1:100 000. This scale is convenient for the overall display of the data and allows for a legible topographic base on which to depict the information. However, all the data are held digitally at larger scales using a Geographical Information System (GIS), which allows easy revision, updating and customisation of the information together with its possible integration with other datasets. The information will form part of a Summary of the Mineral Resources of the South West Region. The purpose of the work is to assist all interested parties involved in the preparation and review of development plans, both in relation to the extraction of minerals and the protection of mineral resources from sterilisation. It provides a knowledge base, in a consistent format, on the nature and extent of mineral resources and the environmental constraints, which may affect their extraction. An important objective is to provide baseline data for the long term. The results may also provide a starting point for discussion on specific planning proposals for minerals extraction or on proposals, which may sterilise resources. It is anticipated that the map and report will also provide valuable background data for a much wider audience, including the different sectors of the minerals industry, other agencies and authorities (e.g. The Planning Inspectorate Agency, the Environment Agency, The Countryside Agency and English Nature), environmental interests and the general public. Basic mineral resource information is essential to support mineral exploration and development activities, for resource management and land-use planning, and to establish baseline data for environmental impact studies and environmental guidelines. It also enables a more sustainable pattern and standard of development to be achieved by valuing mineral resources as national assets. The mineral resources covered are sand and gravel, crushed rock aggregate, brick clay, kaolin, ball clay, building stones, hydrocarbons and metalliferous mineralisation

Exploration for gold in the Crediton Trough, Devon. Part 2 : detailed surveys

This report describes the results of geochemical sampling to trace the source of three groups of highamplitude gold anomalies in panned drainage sediment within the outcrop of the Permian (New Red Sandstone) sedimentary rocks of the Crediton Trough. The sites for follow-up were chosen after appraisal of regional-scale survey data described in the previous report (Cameron et al., 1994). They comprised the Deckport and Solland areas at the western end of the Crediton Trough, and the Smallbrook area adjacent to the faulted southern margin of the Permian rocks some 20 km further east. This work consisted of more detailed drainage sampling and reconnaissance overburden sampling at all three sites, augmented by detailed overburden sampling and the mechanical excavation of a series of pits and trenches at Smallbrook. Microchemical mapping of gold grams from drainage sediment and from excavations in overburden aided the interpretation of the origin of the gold. At Deckport, where the Bow Breccia (Early Permian) is in faulted contact with the Crackington Formation (Late Carboniferous), follow-up sampling indicated strongly that the major source of gold was the Bow Breccia. Telluride inclusions were more frequent in the gold grains from the southern part of the Permian outcrop, than in gold from most other sites in the Crediton Trough. This may indicate that the source is related to a nearby centre of igneous activity, the root of which may be marked by the lamprophyric dykes and vent agglomerate south and south-west of Hatherleigh. The Solland area is immediately east of the trace of a component of the Sticklepath-Lustleigh Fault. Gold persists in drainage sediment towards the southern, faulted contact of the Bow Breccia with Bude Formation (Late Carboniferous) strata to the south. Overburden sampling across the trace of a fault to the east of Solland, parallel to the Sticklepath-Lustleigh Fault, indicated that the gold was not associated with this fault but occurred in alluvial terrace material derived from further south. However, the analysis of overburden samples indicated high values of uranium associated with this fault. At Smallbrook, where the highest-amplitude drainage enrichments in gold had been found, further sampling showed a sharp cut-off for gold just north of the boundary fault with the Crackington Formation. The gold grains from the Small Brook differ from grains from other locations in the Crediton Trough in being finer grained, generally rounded, not enriched in palladium and with fewer and smaller inclusions. Gold was found physically and by analysis in panned overburden pit samples at several sites to the south-east of the Small Brook, particularly in the residual overburden derived from the Newton St Cyres Breccia (Late Permian), to a maximum of fourteen grains from one site. Trenching and pitting confirmed that the shallow overburden samples closely reflected the weathered bedrock beneath. Gold was found (12-35 ppb Au) in several unpanned CO.5 mm fraction samples, but no highly anomalous levels were detected. Microchemical mapping of a gold grain extracted from Newton St Cyres Breccia showed internal chemical characteristics and inclusions identical to grains from the alluvium of the Small Brook, and may indicate an igneous association. The horizontal and vertical distribution of gold in the overburden and weathered bedrock indicate that it is widely dispersed in the Newton St Cyres Breccia in the form of a fossil placer. The source of the gold is probably the older Permian sequence, within which a rich source of mineralisation may exist to the west of Smallbrook. Excavations in alluvium adjacent to the Small Brook indicate the widespread presence of gold (maximum 1180 ppb Au in panned material) from above 1 .O m. Three grains of gold extracted from core from the faulted contact between Permian and Carboniferous rocks in the Upton Pyne Borehole, 5 km east of the Small Brook, were similar in chemistry, but not in shape, to grains from the Small Brook. This discovery reinforces the potential for gold mineralisation close to the contacts, both faulted and unconformable, of the Permian red-bed sequence in Devon. Further work, including drilling, is recommended to determine the concentration of gold in the basal Permian rocks and to determine the potential and controls exerted by Permian igneous rocks on the mineralisation

Geology of the Newquay district : a brief explanation of the geological map Sheet 346 Newquay

This Sheet Explanation presents an account of the geology of the district covered by the Geological 1:50 000 Sheet 346 Newquay, published in 2012. The district is mainly underlain by Upper Palaeozoic rocks of Devonian age. These have undergone deformation in the Variscan Orogeny, a northward propagating mountain building event which commenced in the Devonian in this area, and are variably folded and faulted. Minor granite intrusions of latest Carboniferous to early Permian age occur near the coast and Cenozoic deposits are present locally around St Agnes, in the west. The regional strike in the district, and across the Cornish peninsula, is east–west, so coastal exposures afford a structural crosssection that is almost at right-angles to strike. Several notable early workers commented on aspects of the geology in the district, among them Borlase (1758), Conybeare (1817) and Sedgwick (1820), though the earliest detailed geological notes were published in 1839 by Sir Henry De la Beche, to accompany a geological map published in the same year. Further metalliferous lodes were added subsequently to De la Beche’s map by Sir W W Smyth (1858), and the work was republished in 1866. Survey at the same scale (1:10 560) by Clement Reid, J B Scrivenor and D A MacAlister was carried out around 1900–1905 and published in 1906 at a scale of 1:63 360. A reprint of the Newquay geological sheet, based predominantly on previous work, but converted to the modern 1:50 000 scale, was published in 1974

Exploration for gold in the Crediton Trough, Devon. Part 1 - regional surveys

The results of geochemical surveys in the Crediton Trough of Devon, an area of Permian and Carboniferous rocks, north of Dartmoor, are given in two reports. This report (Part 1) describes the broad-scale drainage and lithogeochemical survey carried out mainly in the area from Hatherleigh in the west, to the valley of the River Exe in the east, over the outcrop of Permian red-bed sediments, minor alkaline basalts and lamprophyric lavas and the surrounding Carboniferous sediments. The Permian outliers at Hollacombe (near Holsworthy), Peppercornbe (near Clovelly), and Holcombe Rogus (southwest of Wellington) together with parts of the Permian outcrop of the Tiverton Basin and west of Cullompton were also sampled. In addition, the results of an interpretation of Landsat Thematic Mapper (TM) imagery over the survey area are presented. Part 2 contains details of follow-up overburden surveys at Deckport, Solland and Smallbrook. The area was selected for gold exploration on the basis of the model of precious metal transport developed to account for the widespread gold in south Devon, which suggested that gold mineralisation might be present in the Permian sequence and the contact with underlying Carbotierous rocks. Drainage surveying confirmed the presence of gold for the first time at numerous localities on the Permian outcrop, and subsequent microchemical mapping of grains demonstrated a number of close similarities with gold from south Devon, strongly suggesting a similar origin. The analysis of rock samples from the Crediton Trough also showed gold to be locally enriched, up to 1.8 ppm in alkaline basalts and up to 42 ppb in samples of Permian sedimentary breccias. Extensive manganese and zinc drainage anomalies at the southern boundary of the Crediton Trough can be related to mineralisation within the Permian and Carboniferous, some of which was worked in the vicinity of Newton St. Cyres. Cinnabar was reported for the first time from this area, and detrital tin, copper and lead anomalies, thought to variously reflect ore minerals or contamination, were also recorded by the drainage survey. The distribution of gold anomalies in the drainage samples indicates that the source is probably associated with the early Permian sediments, the boundary faults between the Permian and Carboniferous sequences, and structures in the Permian, especially where they are underlain by volcanic rocks. Further overburden sampling at three sites is reported in Part 2. Satellite imagery interpretation showed that all the gold anomalies lie on or near lineaments, usually a set trending north-east, which may be more closely associated with mineralising pathways than other directions