Four New Uranium-Lead Ages from Cornwall

R. P. C. Pockley
Department of Geology and Mineralogy, University Museum, Oxford1
1Present address: St. Paul's College, University of Sydney, Newtown, New South Wales.

Summary: Four new isotopic U/Pb ages from Cornwall are reported. The Pb206/U238 and Pb207/U235 ages for each specimen are concordant. The Pb206/U238 ages are : South Terras mine 225 ± 5 million years (Myr.), Redruth Area 124 ± 4 Myr., Wheal Owles mine 58 ± 3 Myr., and South Terras Area 62 ± 3 Myr. Cell sizes, calculated from X-ray powder photographs, decrease with decreasing ages of the specimens, indicating a progressive increase in the oxidation states of the uranium present. It is concluded tentatively that at least two periods of mineralization affected south-west England at about 290 Myr. and 225 Myr., and that a final event occurred at about 60 Myr. Whether this final event involved the remobilization of older uranium with loss of lead, or the introduction of additional uranium, or a combination of both effects cannot be established from this evidence. No unique explanation has been made for the 124 Myr. age.

Mineralogical Magazine; December 1964 v. 33; no. 267; p. 1081-1092; DOI: 10.1180/minmag.1964.033.267.03
© 1964, The Mineralogical Society
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