PhD (M/F) - Dynamics and chronology of a giant uranium system: the McArthur River–Yalowega–Close Lake corridor, southeastern Athabasca Basin

Job Description

Thesis Subject

Unconformity-type uranium deposits are a key research target for the CREGU joint laboratory (CNRS-Orano-Université de Lorraine) due to their status as a significant uranium source for the nuclear industry. The current production is concentrated in the Paleo- to Mesoproterozoic Athabasca Basin in Canada. These deposits are actively explored and mined at the interface between the basin and the underlying basement, as they offer substantial tonnages and—crucially—average uranium grades that can exceed 15%, as seen at the Cigar Lake and McArthur River sites. The formation of such geochemical anomalies required the convergence of highly efficient physical and chemical processes—a subject academic researchers have been investigating for over 60 years. The widely accepted metallogenic model considers that these deposits formed between 1.7 and 1.2 billion years ago through the massive circulation of basin-derived fluids into structural and physicochemical traps located at the intersection between graphitic structures rooted in the basement (known as graphitic conductors) and the Athabasca Basin's unconformity surface.
The deposits are spatially associated with the unconformity between the basin and the basement, and are linked to the structural framework, fluid flow pathways, physical properties of the host medium, and precipitation mechanisms active in this zone. The formation of these hydrothermal deposits at this interface involved intense fluid circulations, evidenced today by clay alteration halos—spanning several kilometers across both the basement and the basin—that surround the uranium mineralization. These alteration patterns vary both between deposits and within individual deposits, with major phases (clays) and minor phases (sulfides, carbonates, APS minerals, etc.) exhibiting various degrees of expression. These phases reflect the differential mobility of various elements (e.g., K for illite, Mg for chlorite, B for tourmaline), driven by changes in physicochemical conditions at the interface over time. Although these hydrothermal markers are broadly spatially associated with uranium mineralization, they remain underused in characterizing the formation and evolution of unconformity-type uranium deposits, as well as in explaining the observed variations in tonnage and uranium grade across different altered zones of the basin. These variations challenge the current metallogenic model, which assumes similar temporal and genetic conditions across the basin. The genetic relationships between the various mineralizing hydrothermal episodes, specific structural settings, multiple fluid events, and distinct hydrothermal mineral assemblages remain poorly understood. In this context, the aim of this PhD thesis is to define the formation dynamics and chronology of the most emblematic hydrothermal and mineralized system in the basin: the McArthur River–Yalowega–Close Lake corridor (southeastern Athabasca Basin).
To achieve this, the thesis will comprise three research axes: Axis 1: mineralogical and physicochemical characterization of the regional-scale alteration halo surrounding the McArthur River–Yalowega–Close Lake corridor. This axis aims to construct an evolutionary model of the hydrothermal events that affected the southeastern Athabasca Basin and currently constitute the regional alteration halo. The model will be based on the study of distinct hydrothermal phases, their spatial distribution, and their paragenetic relationships with respect to uranium mineralization. Axis 2: determination of the structural activity context and its link to mineralization and hydrothermal alteration at the corridor scale. This axis aims to investigate potential changes in the nature and properties of structures along the corridor, in relation to the variations in hydrothermal alteration and mineralization identified in Axis 1. This study will focus on various fault zones within the corridor, involving structural analysis of drill cores and characterization of hydrothermal styles across different structural types and families. Axis 3: chronology of hydrothermal and mineralization events, and generation of a conceptual model for the formation and evolution of the McArthur River–Yalowega–Close Lake uranium-mineralized corridor. The objective is to establish absolute chronological constraints for the structural, hydrothermal, and mineralization episodes identified in Axes 1 and 2, in order to determine the key geological episodes and contexts driving the development of this world-class corridor. Several in situ methods will be tested: Rb-Sr on micas and associated alteration products; K-Ar and/or Ar-Ar on illite; U-Pb on phosphates, carbonates, and TiO₂; and U-Pb on uranium oxides.

Your Work Environment

The PhD project will be conducted primarily at the GeoRessources laboratory in Nancy. It will be supervised by Julien Mercadier (CNRS Research Director) and Gaétan Milesi (Associate Professor, University of Lorraine). The project will be integrated into the CREGU Joint Laboratory (Centre for Research and Study of Uranium Deposits)—a partnership between Orano, the CNRS, and the Université de Lorraine—hosted by GeoRessources. The work will benefit from dual supervision by industrial partners (Orano and Cameco), involving regular progress meetings. Several multi-week field campaigns in Canada are planned to carry out structural measurements, mineralogical characterization, and sampling; these missions will be conducted with the support of both industrial partners. The research will utilize various analytical platforms at GeoRessources and partner laboratories. A range of instruments will be employed to characterize minerals (optical and electron microscopy, µXRF, XRD), measure chemical compositions (electron microprobe, µXRF, LA-ICP-MS, whole-rock geochemistry) and isotopic compositions (LA-ICP-MS, SIMS), and date mineral formation (LA-ICP-MS, SIMS, Ar spectrometry).
The successful candidate will have recently completed a Master's degree in Geosciences, preferably with a focus on hydrothermal systems and/or metal-bearing mineral systems. Proficiency in structural measurements on drill cores and data processing is expected, along with a solid background in mineral observation, characterization and analyses. Analytical and synthesis skills are prerequisites, as is an aptitude for literature review. Proficiency in laboratory techniques and approaches relevant to the study of hydrothermal circulations in the geological settings concerned would be an asset. The candidate should enjoy teamwork within a collaborative project involving both academia and industry, including English-speaking scientists. candidate must be autonomous, proactive, and capable of proposing new ideas.

Constraints and risks

none

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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