The discover of brannerite and uraninite in lower cambrian U-bearing phosphorite in west Hunan

Microcrystalline uraninite and microcrystalline orthobrannerite, (monoclinic) brannerite are discovered for the first time in polymetallic uranium phosphate rocks of the lower Cambrian series Niutitang group black shale system in West Hunan by the way of electron probe micro-analyser and SEM to the etched alpha-particle track. The three primary uranium minerals are paragenetic and also coexisted with Mo, Ni, Pb. Zn, Cu, V and Fe sulfides. The minerals mainly occurred in embryo crystalline graphite of polymetallic quartz phosphate rocks which is closely related to carbone and also in quartz and the early formed C-S-Mo ore fragments. Orthorbrannerite is elongated, brannerite is short cylindrical or granular, uraninites are mostly xenomorphic granular and some are automorphic and hypidiomorphic octagon crystal. The minerals are all microcrystalline with grain size mostly in the range of 1-5 μm and aggregates up to 10-20 μm. Further study shows that the formation of orthobrannerite and brannerite is the result of submarine gas phase ejection and condensation of uranium hydrogen compounds. (author)