The discovery of onofrite and uraninite in marine phosphorite and its geological significance, northwestern Hunan

Nano-scale onofrite and uraninite were firstly discovered in oolitic phosphorite in lower part of lower Cambrian marine black rock series in Niutitang formation, Wulin area, northwestern Hunan of the Southeast Yangtze plate. The occurring state, morphologic characteristics and occupancy characteristics of onofrite and uraninite in marine phosophorite have been identified through detecting the chemical composition by electron probe and micro-anatomy. Studies suggest that oolitic phosphorite of syn-sedimentation (oolite contains globular onofrite) accompany with volcanic hydrothermal ejection, nanoscale onofrite emplaced in the interior and center of super fine nanoscale phosphorite nodule, in the later synsedimention, sea bottom hydrothermally process was continued, phosphorite was partially corroded and hydrothermally decarburized, uraninite and quartz was precipitated in micro fissure of phosphorite. The discovery of onofrite and uraninite and the emplacing characteristics research was helpful to find out the formation of onofrite in phosphorite and the way of occurrence and genetic relationships of submarine exhalation (thermal water) sedimentation. Which further proved that the exhalative sedimentary is the mechanism of large-scale uranium mineralization in the east Yangtze plate. (authors)