CDUT's Latest Research Reveals the Reductant Problem of the World's Richest Uranium Deposit
Any change in the redox environment is of great significance to control the migration and precipitation of uranium, a typical variable valence metal element in nature. When it comes to nature, however, it is very complicated to determine what kind of substance causes the change in the redox environment and how it results in substance precipitation.
Recently, The role of graphite in the formation of unconformity-related uranium deposits of the Athabasca Basin, Canada: a case study of Raman spectroscopy of graphite from the world-class Phoenix uranium deposit, a research achievement of Prof. Song Hao from the Department of Geochemistry, College of Earth Sciences, Chengdu University of Technology (the first author), Prof. Chi Guoxiang from the University of Regina, Canada (the corresponding author), and Prof. Li Zenghua from the East China University of Technology, and his Canadian collaborators, was officially published in the American Mineralogist (AM), one of the most authoritative international academic journals in the field of geoscience and a highly-influential academic journal in the fields of mineralogy, petrology and ore deposits. It is learned that this is the first paper published by the university’s faculty as the first author in the AM, which marks a new breakthrough in the internationalization of uranium geology research and an important progress in mineralogy and uranium metallogenic mechanism both made by Chengdu University of Technology.
Graphite is one of the common minerals in nature and deemed as an important reducing agent, which depends on the specific environment. Phoenix (average minerals up to 19.13 wt.% U3O8 - 71.3 million pounds U3O8), the world's richest known large uranium deposit, was selected as the subject of the study. The deposit is located in the Athabasca Basin in northern Saskatchewan, Canada, where unconformity-related uranium minerals are generally in high grades, many of which are above 2 wt.% and several even above 15 wt.%. According to previous studies, there is some consensus on the genesis of the unconformity-related uranium mineral there, — the mineralizing fluid is mainly oxidized basin brine which extracts U as it flows through the basin and basement to form U-rich fluid, and this fluid encounters reducing fluid from the basement near the unconformity surface or reacts with the reduction-rich rocks of the basement, so the U in the fluid changes from U6+ to U4+, with pitchblende precipitated. In this regard, the reducing substances remain more controversial. For example, (1) graphite is directly involved in chemical reactions related to uranium reduction precipitation; (2) graphite is indirectly involved in the reaction process of mineralizing fluids as a provider of hydrocarbons; and (3) graphite is not involved in chemical reactions, but it can promote the formation of mineralized structures due to its special physical properties.
Figure 1. Graphite with different morphology in core samples
Figure 2. Graphite coexisting with gaseous reducing agent
Figure 3. Graphite Raman feature parameters and their relationship with depth
In response to these controversies, the study directly focused on graphite to explore mineralogical spatial zonation profiling. Based on petrography, the laser Raman was adopted as the main method to quantify and analyze the order degree of graphite through the resolution of graphite Raman spectral lines. The results show that the variation pattern of graphite characteristics with depth does not support the view that graphite as a reducing agent directly leads to uranium precipitation. The disorder of graphite degree near the unconformity surface is more likely to be a result of paleo-weathering and prolonged basin fluid action. In order to explain the spatial relationship between uranium mineral and graphite-rich basement faults, the research group proposed new views and models that graphite acts as a lubricant to promote fracture activity, deep graphite provides reductants such as hydrocarbons and hydrogen, and shallow suction pumps and deep fault valves jointly control fluid activity to periodically transport reducing gases to the vicinity of unconformity surface to participate in redox reactions for mineralization, taking into account what the research group newly learned from their study over the periodic activity of mineral-controlling fractures through fluid inclusions and numerical simulations of fluid dynamics.
Chengdu University of Technology (CDUT) has long valued international cooperation and foreign exchange. Without the support from the China Scholarship Council and the Natural Science Foundation Program of the Canadian government, this result might not be achieved. It also demonstrates CDUT's emphasis and strong support for international cooperation and original and high-quality scientific research results. (Mount Everest Uranium Research Team of Chengdu University of Technology)
Link to the full text: https://doi.org/10.2138/2022-8158
Figure 4. Unconformity surface uranium metallogenic model
