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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Iron oxyhydroxides are among the most important colloids that control rare earth elements (REE) concentrations and transport in natural hydrosystems. In this study, REE surface complexation to iron oxyhydroxides (Fe(OH) 3 (a)) was described by using the Donnan diffuse layer model and a two-site (i.e. ≡Fe s OH and ≡Fe w OH) model. The specific surface area and pH of zero charge were fixed as 100000 m 2 /mol and 8.0, respectively. The surface site density for weak and strong binding sites were fixed at 0.1 mol/mol Fe (≡Fe w OH) and 0.001 mol/mol Fe (≡Fe s OH) respectively. The two site types were used with pK a1 int = 7.29 and pK a2 int = 8.93. Using linear free energy relationship, the estimated equilibrium surface complexation constants (log K) increased from light REE (LREE) to heavy REE (HREE). Results of REE modeling calculation using the determined log K revealed a good fit of experimental data, showing an order of sorption on iron oxyhydroxides: HREE > MREE > LREE and preferential sorption of HREE at a lower pH. However, sorption edges only showed a slight change with ionic strength (0.1 to 0.7 mol/L) for the whole REE series. The generalized model was subsequently used to evaluate the impact of iron oxyhydroxides on REE speciation in groundwater. Application of the model to "model groundwater" showed that iron oxyhydroxide complexes of REE were significant in near neutral and weakly alkaline pH. This study contributes to putting forward a comprehensive database which would be useful for the application of surface complexation model to describe REE sorption by amorphous ferric hydroxides in nature.

A methodology for the determination of the rare earth elements in uranium oxides by ion microprobe has been set up on a Cameca ims‐3f instrument. An uranium oxide reference material from a syn‐metamorphic uranium deposit related to albitisation has also been developed for this type of analysis. Applications of the methodology are presented for a series of uranium oxides selected from some major uranium deposit types: from the world's highest grade unconformity‐related uranium deposit from the Athabasca Basin (Saskatchewan, Canada; the Shea Creek and the McArthur River examples), a perigranitic vein‐type deposit (Pen Ar Ran, Vendée, France) and a volcanic caldera‐related deposit (Streltsovkoye, Transbaikalia, Russia). Each type of uranium deposit appears to have a specific REE signature. All REE patterns from the Shea Creek and the McArthur deposits are characterised by bell‐shaped patterns centred on Tb‐Dy and similar to those already published for uranium oxides from unconformity‐related deposits from Australia. Such bell‐shaped REE patterns centred on Tb‐Dy may therefore be considered as a typical signature of uranium oxides from Mesoproterozoic unconformity‐related deposits. A smoother bell shape pattern centred on Eu characterises the syn‐metamorphic albitisation related deposit of Mistamisk selected for the reference material. The REE patterns from the Pen Ar Ran deposit show a fractionation from LREE to HREE with anomalously high abundances of Sm, Eu and Gd with respect to the other REEs, similar to the REE patterns of uranium oxides from the volcanic‐related deposits of Streltsovkoye.

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