Coupled uranium mineralisation and bacterial sulphate reduction for the genesis of the Baxingtu sandstone-hosted U deposit, SW Songliao Basin, NE China

• Published in: Ore geology reviews 2017-04, Vol.82, p.108-129
• Main Authors: Bonnetti, Christophe, Liu, Xiaodong, Zhaobin, Yan, Cuney, Michel, Michels, Raymond, Malartre, Fabrice, Mercadier, Julien, Cai, Jiangfang
• Format: Article
• Language: English
• Subjects: Bacterial sulphate reduction; Sandstone-hosted uranium deposit; Sciences of the Universe; Songliao Basin; Uranium bioreduction; Yaojia Formation
• ISSN: 0169-1368; 1872-7360
• DOI: 10.1016/j.oregeorev.2016.11.013

[Display omitted] •U deposits are hosted in sandstones of the Late Cretaceous Yaojia Formation.•Pre-ore U concentrations on altered Fe-Ti oxides and organic matter.•Organic matter is mainly inherited from land plants and of type III–IV kerogens.•Ore-stage iron disulphides are mainly of biogenic origin.•Uranium mineralisation precipitated during bacterial sulphate reduction. The Baxingtu deposit is a typical redox front tabular-shaped uranium deposit hosted in sandstones of the Late Cretaceous Yaojia Formation deposited within a braided river environment during the post-rift stage of the Songliao Basin, in northeast China. This study proposes the first metallogenic model for the Baxingtu deposit and provides new data on genetic processes involved in the uranium mineralisation of sandstone-type deposits that were characterised through petrographic observations, whole-rock geochemistry, and geochemical and/or mineralogical study of iron disulphide, uranium minerals, Fe-Ti oxides (EPMA, LA-ICP-MS), and organic matter (REP). The δ34S value has been measured in situ by SIMS on the different generations of iron disulphide. Within regional primary reduced sandstones, pre-ore uranium enrichment (Umean=7.6ppm in whole rock) was identified on altered Fe-Ti oxides along with minor concentrations on organic matter (respectively 26.3% and 1.3% of the whole-rock U content), which together represent a significant source of uranium for the mineralisation. Additional pre-ore uranium concentrations may also be associated with clay minerals. Petrographic observations and REP data indicate that organic matter occurring in the host-sandstone is mainly inherited from land plants and corresponds to type III or type IV kerogens. Ore-stage iron disulphides largely occur as framboids and in replacement of organic matter or also as sub-idiomorphic to idiomorphic cement and crystal. Trace element signatures detected within framboids are likely indicative of formation mainly from a single event. Framboids and iron disulphide in replacement of organic matter have a light sulphur isotope signature characterised by δ34S values from −72.0 to −6.2‰, suggesting that sulphur originated from bacterial sulphate reduction, which was mainly responsible for (1) the liberation of U from Fe-Ti oxides and organic matter, (2) the generation of ore-stage iron disulphides, (3) the bioreduction of uranium and (4) the production of a secondary H2S-rich reducing barrier also involved in uranium reduction.