Terra Nova, 23, 264–269, 2011 Abstract Uranium deposits form in a wide range of geological settings, including deep magmatic to surficial conditions, and range in age from Archaean to recent. These temporal and spatial variations have given rise to an extreme diversity of ore deposits. However, understanding their conditions of formation has remained challenging. This article reports rare earth element (REE) abundances, measured by microbeam methods in uranium oxides, for a series of worldwide uranium occurrences. The REE patterns are very specific to each deposit type and directly reflect the conditions of their genesis. We propose an evaluation of the first‐order parameters controlling the REE behaviour in each mineralised system. This study demonstrates that the REE pattern is the most efficient tool for constraining the geological models of uranium deposits and for genetically discriminating new uranium discoveries. This approach may form the starting point for a new procedure in the fight against nuclear trafficking. Terra Nova, 00, 1–6, 2011

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Several diagenetic models have been proposed for Middle and Upper Jurassic carbonates of the eastern Paris Basin. The paragenetic sequences are compared in both aquifers to propose a diagenetic model for the Middle and Late Jurassic deposits as a whole. Petrographic (optical and cathodoluminescence microscopy), structural (fracture orientations) and geochemical (δ 18 O, δ 13 C, REE) studies were conducted to characterize diagenetic cements, with a focus on blocky calcite

Columbite-tantalite group minerals are the most common Nb-Ta minerals. Columbite-tantalite is particularly suitable for U-Pb dating due to its high U and low common Pb contents. In situ isotopic dating of columbite-tantalite by LA-ICP-MS or SIMS requires certified reference material to properly account for potential matrix effects linked to substitutions between Nb and Ta and between Mn and Fe. Our study has two objectives: i) establish a database of reference materials for in situ U-Pb isotopic dating of columbite-tantalite minerals and ii) test the capability of SIMS to in situ U-Pb date columbite-tantalite minerals of different chemical composition. Tests of in situ U-Pb dating demonstrate that SIMS can easily be used to date columbite-tantalite minerals with errors and precisions overlapping the reference ID-TIMS age. There are, however, significant matrix effects for non-matching Nb-Ta-Fe-Mn compositions of sample and reference material. Matrix effects are highly correlated with the Ta/(Ta+Nb) ratio of columbite-tantalite, due to the significant difference in the atomic mass of Nb and Ta. The Mn/(Mn+Fe) ratio does not significantly contribute to the observed matrix effect as the two elements have similar atomic masses. The linear correlation between Ta/(Nb+Ta) and ((206 Pb/ 238 U) SIMS /(206 Pb/ 238 U) ID-TIMS) obtained for columbite-tantalite minerals of known ID-TIMS age demonstrates that the SIMS matrix-effect can be properly accounted for by using the chemical composition as determined by EMPA. The ability to measure 204 Pb by SIMS also allows the use of reference materials with a small common lead contribution and to calculate accurate and precise ages for columbite-tantalite minerals with contributions of common lead.