湘西北海相含铀磷块岩中硒汞矿和晶质铀矿的发现及其地质意义

The Discovery of Onofrite and Uraninite in Marine Phosphorite and Its Geological Significance,Northwestern Hunan

在扬子陆块东南缘湘西北武陵地区下寒武统牛蹄塘组海相黑色岩系下部鲕粒磷块岩中,首次发现了似纳米级的硒汞矿和晶质铀矿。通过电子探针化学成分测定和微区解剖,显示海相磷块岩中硒汞矿和晶质铀矿的产出状态、形态特征和占位特征。研究认为,同沉积期伴随火山热液喷出形成海相沉积鲕粒状磷块岩(鲕粒中包含球滴状硒汞矿),似纳米级硒汞矿在海相磷块岩中占位于鲕粒磷结核的内部和中心。其形成后期,海底热液作用持续,磷块岩经部分溶蚀、热液脱碳,在磷块岩的微裂隙中晶质铀矿、石英共沉淀析出。海相磷块岩中硒汞矿和晶质铀矿的发现和空间占位特征的研究,对探讨磷块岩中硒汞矿和晶质铀矿的形成与海底喷流(热水)沉积作用的发生方式和成因联系有启示意义,进一步佐证扬子陆块东缘陆缘裂陷喷气沉积是发生大规模铀成矿作用的机制。

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 characteris- tics 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 - sedi- mentation （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 phosphor- ite. 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 subma- rine exhalation （thermal water） sedimentation. Which further proved that the exhalative sedimentary is the mechanism of large- scale uranium mineralization in the east Yangtze plate.