Location of Repository

An airborne geophysical survey of part of west Dyfed, South Wales, and some related ground surveys

By J.D. Cornwell and R. Cave

Abstract

A detailed airborne geophysical survey has been made of\ud part of west Dyfed at a flying height of 75 m with\ud magnetic, electromagnetic (VLF-EM) and radiometric\ud equipment mounted in a helicopter. The area of 670 km2\ud includes the Precambrian anticlines of St David’s and\ud Hayscastle, the Fishguard, Sealyham and Trefgarne\ud volcanic groups, and the adjacent Lower Palaeozoic\ud sediments with associated basic intrusions.\ud Ground geophysical surveys were carried out at 33\ud localities to confirm the nature and the sources of the airborne\ud anomalies, and a geological examination was also\ud made at selected localities. Rock samples were collected\ud for petrographical examination and physical property\ud determinations. A regional gravity survey was also carried\ud out.\ud Some details of the geophysical methods and data\ud presentation are included together with a map at a scale of\ud 1:50 000 summarising the main results obtained from interpretations\ud of the airborne geophysical surveys.\ud The aeromagnetic data clearly show the distribution of\ud the Precambrian rocks, the numerous dolerite intrusions,\ud and some of the pillow lavas associated with the Fishguard\ud Volcanic Group. This distribution generally confirms the\ud outcrop pattern based on geological mapping. The\ud magnetic data are likely to be more reliable for mapping\ud on a more detailed scale, due to the extensive drift cover\ud which hinders geological mapping in many places, and\ud they have also revealed some large scale structures, in-\ud The airborne VLF anomalies are most obvious at\ud lithological boundaries with large resistivity contrasts\ud such as the Precambrian/Lower Palaeozoic sediment and\ud dolerite/sediment contacts. The radiometric data provide\ud little obvious additional information.\ud Although the west Dyfed area has no significant mining\ud history, some exploration activity has taken place there in\ud recent years (Allen, Cooper and others 1985; Cameron\ud and others, 1984; Brown and others, 1987). One of the\ud main restrictions on exploration has been the lack of rock\ud exposure in much of the inland area and the airborne\ud geophysical survey was undertaken as partial compensation\ud for this

Topics: Earth Sciences
Publisher: British Geological Survey
Year: 1986
OAI identifier: oai:nora.nerc.ac.uk:11812

Suggested articles

Preview

Citations

  1. (1984). A geochemical drainage survey of the Preseli Hills, south-west Dyfed,
  2. (1980). A topographic correction for VLF-EM profiles based on model studies.
  3. (1965). Aeromagnetic map of Great Britain, 1:625 000, Sheet 2. Southampton : Ordnance Survey.
  4. (1981). An airborne geophysical survey of the Whin Sill between Haltwhistle and Scot’s Gap, south Northumberland. Miner. Reconnaissance Programme Rep.
  5. (1965). Bouguer gravity anomalies in Wales.
  6. (1979). Early Ordovician volcanism in
  7. (1985). Exploration for porphyry-style copper mineralisation near Llandeloy, south-west Dyfed. Miner. Reconnaissance Programme Rep.
  8. (1983). Geophysical investigations in the Variscides of South-west Britain.
  9. (1985). K:Ar age determinations on a dolerite dyke from Dyfed, South Wales. Isotope Geol.
  10. (1983). Linear filtering of VLF dip-angle measurements.
  11. (1983). Low-grade metamorphism within the Welsh sector of the paratectonic Caledonides.
  12. (1971). Metal mines of southern Wales.
  13. (1979). Mineral exploration in the Harlech Dome, North Wales. Miner. Reconnaissance Programme Rep.
  14. (1912). On the pre-Cambrian rocks of Brawdy, Hayscatle and Brimaston (Pembrokeshire). doi
  15. (1973). Palaeomagnetic studies in the British Caledonides-V. Miscellaneous New Data. doi
  16. Pillow lava and isolated-pillow breccia of rhyodacitic composition from the Fishguard Volcanic Group, Lower Ordovician, SW Wales, United Kingdom.
  17. (1979). Report on the helicopter-borne geophysical survey in three selected areas of the British Isles on behalf of the Institute of Geological Sciences, Natural Environment Research Council (unpublished). Sander Geophysics Limited.
  18. (1973). St David’s 1:25 000 scale geological map sheet. Southampton : Ordnance Survey.
  19. (1969). The composite nature of the St David’s Head and Carn Llidi intrusions of North Pembrokeshire. In
  20. (1930). The geology of Ramsey Island (Pembrokeshire). doi
  21. (1915). The geology of the district between Abereiddy and Abercastle.
  22. (1945). The geology of the Prescelly Hills, north Pembrokeshire.
  23. (1981). The petrology of the Lower Palaeozoic Fishguard Volcanic Group and associated rocks E. doi
  24. (1962). The sequence and correlation of the Coal Measures of Pembrokeshire.
  25. (1956). The volcanic rocks of the area between Fishguard and Strumble Head, doi
  26. (1924). The volcanic Series of Trefgarn, doi
  27. (1987). Volcanogenic mineralisation in the Treffgarne area, south-west Dyfed,

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.