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| Titel: |
A Rapid In Situ Method for Determining the Ages of Uranium Oxide Minerals: Evolution of the Cigar Lake Deposit, Athabasca Basin |
| Auteur: |
Fayek, Mostafa Harrison, T. Grove, Marty Coath, Christopher |
| Verschenen in: |
International geology review |
| Paginering: | Jaargang 42 (2000) nr. 2 pagina's 163-171 |
| Jaar: |
2000-02 |
| Inhoud: |
We present a rapid and accurate technique for making in situ U-Pb isotopic measurements of uranium oxide minerals that utilizes both electron and ion microprobes. U and Pb concentrations are determined using an electron microprobe, whereas the isotopic composition of Pb for the same area is measured using a high-resolution ion microprobe. The advantages of this approach are: mineral separation and chemical digestion are unnecessary; homogenous uranium oxide standards, which are difficult to obtain, are not required; and precise and accurate U-Pb ages on ∼10 μm spots can be obtained in a matter of hours. We have applied our method to study the distribution of U-Pb ages in complexly intergrown uranium oxides from the unconformity-type Cigar Lake uranium deposit, Saskatchewan, Canada. In situ U-Pb results from early formed uraninite define a well-correlated array on concordia with upper and lower intercepts of 1467 ± 63 Ma and 443 ± 96 Ma (±lσ), respectively. The 1467 Ma age is interpreted as the minimum age of mineralization and is consistent with the age of clay-mineral alteration (∼1477 Ma) and magnetization of diagenetic hematite (1650 to 1450 Ma) that is associated with these unconformity-type uranium deposits and early diagenesis of the Athabasca Basin sediments. In situ U-Pb isotopic analyses of uraninite and coffinite can document the Pb∗/U heterogeneities that can occur on a scale of 15 to 30 μm, thus providing relatively accurate information regarding the timing of fluid interactions associated with the evolution of these deposits. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
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