湘西下寒武统含铀磷块岩中钛铀矿和晶质铀矿的发现及其成因分析

摘要

Microcrystalline uraninite and microcrystalline orthobrannerite,(monoclinic)brannerite are discovered for the first time in polymetallic uranium phosphate rocks of the lower Cambrian series Niuti-tang 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—5μm and aggregates up to 10—20μm.Further study shew that the formation of orthobrannerite and brannerite is the result of submarine gas phase ej ection and condensation of uranium hydrogen compounds.%对湘西下寒武统牛蹄塘组黑色页岩系中的含铀多金属磷块岩,笔者通过α径迹法示踪,先后采用电子探针、扫描电镜及透射电镜进行成分和结构分析,首次在其中发现了微晶状的晶质铀矿、斜方钛铀矿和钛铀矿.这3种铀矿物密切共生,也与钼、镍、铅、锌、铜、钒、铁等的硫化物共生,主要赋存于多金属磷块岩的雏晶石墨中,与碳的关系密切；其次也赋存于石英和先期形成的碳硫钼矿碎片中.斜方钛铀矿呈长柱状,钛铀矿呈短柱状和粒状,晶质铀矿多呈它形粒状,少数呈八边形自形、半自形晶.矿物粒径多在1~5μm,集合体可达10~20μm.进一步的成因研究表明,钛铀矿和晶质铀矿由高温铀氢化合物海底气相喷出凝聚所形成.