Ages of Uraninite and Coffinite from South-West England

A. G. Darnley, T. H. English, Mrs. O. Sprake, E. R. Preece and D. Avery
Atomic Energy Division, Geological Survey of Great Britain
National Chemical Laboratory, Teddington, Middlesex
Atomic Energy Research Establishment, Harwell, Berkshire

Summary: The mode of occurrence of uraninite, pitchblende and coffinite at five localities in south-west England is described. Chemical and isotopic analyses of concentrates containing these minerals provide the following 206Pb/238U ages (My.): uraninite, South Crofty, Cornwall, 277 ± 10; uraninite, Geevor, Cornwall, 223 ± 5; pitcbblende-coffinite, King's Wood, Devon, 206 ± 5; pitchblende, Wheal Bray, Cornwall, 165 ± 4; pitchblende, South Terras, Cornwall, 474 ± 2; coffinite, Geevor, Cornwall, c. 45 (chemical analysis only). These results are compatible with geolo-gical and mineralogical evidence. Consideration of these and other results indicates that there were at least three periods of uranium mineralization in south-west England, at c. 290 My., c. 225 My., and c. 50 My. Other intermediate ages may also be valid but further work is required to substantiate these.

Mineralogical Magazine; 1965 v. 34; no. 268; p. 159-176; DOI: 10.1180/minmag.1965.034.268.13
© 1965, The Mineralogical Society
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