遵义松林地区下寒武统多金属磷块岩矿物组成及铀的存在形式

含铀磷块岩是中国非常规铀资源的重要类型之一,其铀的存在形式及赋存状态一直存在争议。笔者对贵州省遵义松林地区的多金属磷块岩进行了化学成分和微量元素分析,以及扫描电镜研究,结果表明:区内多金属磷块岩中Ba含量高达2339×10~(-6),Sr/Ba值为0.33~2.48,U/Th值为118~544;在Fe/Ti-Al/(Al+Fe+Mn)图中,投影点落在热水沉积区。这反映了多金属磷块岩成因上与热水沉积作用有联系。该类岩石中含有方硫镍矿、辉砷镍矿、针镍矿、辉钼矿、黄铁矿、闪锌矿、重晶石等热液成因矿物,以及鲕粒磷灰石、胶状磷灰石、重结晶磷灰石和晶质铀矿,也指示其受热水沉积作用的影响。由此认为,区内多金属磷块岩在沉积成岩过程中,携带矿质(Ni、Mo、As、Zn、Ba、U等)的热液随着温度、压力的降低,在磷块岩的微裂隙和微孔隙中共沉淀,并析出晶质铀矿和其他多金属矿物。存在于多金属磷块岩微裂隙和微孔隙中的独立铀矿物的发现,为该类型非常规铀资源的综合开发利用提供了有利依据。

Mineral Composition and Uranium Existing Form of Polymetallic Phosphorite in Songlin Area,Zunyi

Uraniferous phosphorite is an important type unconventional uranium resources.The uranium existing form and occurrence are in disputation.In this paper,the element geochemical analysis and scanning electron microscopy (SEM) were used to study the polymetallic phosphorite in Songlin area of Zunyi,Guizhou province.Ba content in the polymetallic phosphorite was found up to 2339 × 10-6,Sr/Ba was 0.33～2.48,U/Th was 118～544;Fe/Ti-Al/ (Al+Fe+Mn) diagram of polymetallic phosphorite was found to fall into hydrothermal sedimentation area and the main minerals of Songlin polymetallic phosphorite are of hydrothermal genesis (vaesite,gersdorffite,millerite,molybdenite,pyrite,sphalerite,barite),oolitic apatite,colloidal apatite,recrystallization apatite and uraninite,which suggest that the polymetallic phosphorite of the Lower Cambrian Niutitang Formation was affected by hydrothermal sedimentation.With the decrease of temperature and pressure,uraninite and polymetallic minerals were separated out by co-precipitation in micro pores and micro cracks of phosphorite.The discover of uraninite existed in micro pores and micro cracks of phosphorite will provide basic data for comprehensive utilization of this type unconventional uranium resources.