The Potential of Rare Earth Elements for Revealing the Conditions of Uranium Deposit Formation and their Subsequent use for Exploration and Uranium Forensic Issues

English Abstract:

Uranium deposits are known to be formed in a wide range of geological settings including deep metamorphic/magmatic to surficial conditions and range in age from Archean to recent time. These temporal and spatial variations have given rise to an extreme diversity of U deposits. However, understanding their genesis and thereafter exploring for uranium deposits have remained challenging. In particular, very limited link between trace elements or isotopic composition of uranium oxide and the conditions for their accumulation to economic grades have been clearly established.

Natural uranium oxides (UO2) bear variable quantities of minor and traces elements (< 1 ppm and up to several pourcents) which have been more and more used to better understand the primary conditions of ore formation but also alteration processes which have potentially posteriorly affected them. Consequently, the quantification of trace elements in UO2 and the measurement of their isotopic ratio(s) have been a major research direction to better understand geologically the uranium deposits but also to fight against nuclear proliferation via forensic programs.

The present contribution aims to synthetize the recent developments in the use of Rare Earth Elements (REE) to uranium geological and forensic applications. The first part will emphasize on the last analytical developments to measure this group of elements by in-situ techniques (SIMS and LA-ICP-MS). The second part will present case studies of application of these techniques on several deposits to demonstrate that the REE contents of uranium oxides are very specific to each deposit type, regardless of the age or variations in local geological settings, and that the REE abundances reflect directly the mineralising processes specific to each deposit type. An evaluation of the first order parameters (T, REE sources and fluid composition) controlling the REE behaviour in each mineralized system is proposed. The last part will present some results and potential developments on the use of REE for forensic issues with comparison between some ore mineralization and the subsequent Yellow Cake to consider the limits of this technique in helping tracking the U production.