The relative mobility of U, Th and Ra isotopes in the weathered zones of the Eye-Dashwa Lakes granite pluton, northwestern Ontario, Canada

Journal Article · Thu Oct 01 04:00:00 EDT 1987 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(87)90158-X· OSTI ID:7255877

Latham, A G ^[1]; Schwarcz, H P ^[2]

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1. Geological Survey of Canada, Ottawa, Ontario (Canada)
2. McMaster Univ., Hamilton, Ontario (Canada)

Radioisotope activity ratios of weathered surface rocks from the Eye-Dashwa Lakes granite pluton show that, in the {sup 238}U decay series, {sup 226}Ra has been leached more rapidly than the grandparent {sup 234}U and {sup 238}U isotopes. The observation of {sup 238}Th/{sup 232}Th disequilibria in the {sup 232}Th decay series shows that either {sup 228}Th (half-life of 1.9 yrs) or {sup 228}Ra (half-life of 5.75 yrs) have been removed from these rocks very rapidly indeed. Isotope ratios of separated mineral fractions appear to show that whereas uranium tends to be removed from all mineral fractions, Ra is strongly readsorbed onto feldspars, presumably as these undergo alteration to clay minerals. This necessitates making a distinction between intermineral mobility of U or Ra, and the net loss of U or Ra from the whole rock. An attempt has been made to model, quantitatively, the transport rate of Ra, though with little success. Failure of the modelling appears to indicate that the mobility of {sup 228}Ra is higher than might be predicted by the mobility of {sup 226}Ra; that is, the two isotopes are not strict analogues of one another in their response to initial weathering.

• OSTI ID: 7255877
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 51:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540230* -- Environment
Terrestrial-- Radioactive Materials Monitoring & Transport-- (1990-)
58 GEOSCIENCES
580000 -- Geosciences
ACTINIDE ISOTOPES
ALKALINE EARTH ISOTOPES
CANADA
CHEMISTRY
DISSOLUTION
ENVIRONMENTAL TRANSPORT
GEOCHEMISTRY
GRANITES
IGNEOUS ROCKS
ISOTOPES
LEACHING
MASS TRANSFER
NORTH AMERICA
ONTARIO
PLUTONIC ROCKS
RADIOISOTOPES
RADIONUCLIDE KINETICS
RADIONUCLIDE MIGRATION
RADIUM ISOTOPES
ROCKS
SEPARATION PROCESSES
THORIUM ISOTOPES
URANIUM ISOTOPES
WEATHERING