ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The distribution of uranium in intercumulus minerals of the Rhum layered intrusion, Inner Hebrides, has been studied by the fission track technique. A striking feature was the frequent occurrence of intense fission track stars recorded on the organic solid state nuclear track detectors. The high uranium sources corresponding to such features were found to be small, discrete mineral phases, often not larger than 50 μm in size. The phases were identified as the zirconium- or phosphorus-bearing minerals zirconolite (essentially (CaFe)(Zr)(Ti)2O7), baddeleyite, zircon and apatite. Although zirconolite and baddeleyite frequently coexist in mesostasis areas of lunar mare basalts, baddeleyite has been only rarely observed, and zirconolite not yet reported in terrestrial basalts, with this being the first recorded occurrence of zirconolite and baddeleyite from a terrestrial ultrabasic cumulate. From estimated uranium concentrations, all of which exceed 50 p.p.m., the uranium values decrease in the order zirconolite, baddeleyite, zircon, apatite. The mesostasis areas in which these minerals occur, are to a certain extent determined by the pre-existing cumulus mineral morphologies. Branching, or “cup-shaped”, olivines provide small scale hollows in which residual magmatic fluids become trapped. Such fluids clearly concentrate those elements not incorporated into the cumulus phases, e.g. uranium, phosphorus, zirconium, etc., and crystallise to give uranium-enriched minerals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00376083
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