Physics
Scientific paper
Nov 1962
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1962gecoa..26.1137p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 26, Issue 11, pp.1137-1146
Physics
3
Scientific paper
Eleven samples representing a pre-Pennsylvanian weathering profile on the Boulder Creek granodiorite near Boulder, Colorado, have been analysed for thorium and uranium by -ray spectrometric and chemical methods. In an effort to determine the possible sites of thorium and uranium in these samples, a study of their leachability in hot 2 N hydrochloric acid was undertaken. The fresh granodiorite was found to contain 9·3 p.p.m. thorium and 2·5 p.p.m. uranium. The first stages of weathering resulted in an apparent removal of 25 per cent of the thorium and 60 per cent of the uranium present in the original granodiorite. The leaching study of the fresh granodiorite demonstrated that as much as 90 per cent of the thorium and 60 per cent of the uranium could be removed by an acid leach solution. This seems to indicate that most of the thorium and uranium in the fresh rock is situated in acid soluble minerals or in interstitial materials. After the initial drop of the concentration in the lowest part of the weathered mantle, the total uranium and thorium content of the weathered rock increases by a factor of at least 4 in the uppermost, most-weathered rock material. Leaching studies of the weathered rock indicate that uranium is present largely in the primary resistates, such as zircon, xenotime, and apatite, and thorium occurs mainly in or on clays or in the secondary resistates--minerals formed during weathering.
Adams John A. S.
Pliler R.
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