若尔盖铀矿田含矿岩系的岩石特征及成因探讨

通过对川西若尔盖铀矿田含矿岩系的宏观产状和显微岩石学特征的研究,认为该铀矿田的三套含矿地层主要有硅岩、灰岩、板岩三种岩石类型.其中,硅岩包括了泥晶硅岩、变晶硅岩、硅化(交代)硅岩、钙化硅岩;其成因有两类,产于泥质板岩夹层中的薄层状硅岩是生物化学沉积形成的,而以不规则透镜状产于灰岩层内及其上、下部的硅岩则属于灰岩受后期硅化交代而成.灰岩包括砂质细晶灰岩、硅化球粒灰岩、硅化泥晶灰岩三种;砂质细晶灰岩系混积陆棚环境的产物,硅化球粒灰岩、硅化泥晶灰岩系生物、生物化学成因的泥晶灰岩经硅化而成.板岩包括泥质板岩、砂板岩、千枚状板岩三类,系陆棚环境细碎屑岩经区域变质而成.三类岩石的宏观和微观特征反映出若尔盖铀成矿区早志留世为陆棚环境,海平面的升降使沉积环境在内陆棚与外陆棚之间变换.在剖面结构上,表现为砂质板岩-粉砂质板岩-泥板岩(泥晶灰岩)-页岩-硅岩的韵律性叠置.

Petrology and genesis of ore-bearing rock series in the Zoige uranium ore field, Sichuan, China

This paper examines the macroscopic occurrence and microscopic petrology of the ore-bearing rock series in the Zoige uranium ore field and considers silicalite,limestone,and slate as the main rock types of the ore-bearing strata,namely Yangchanggou Formation,Ta'er Formation and Lalong Formation in Lower Silurian in this field.Silicalite includes micritic,blastic,silicified and calcified silicalite,with two kinds of genesis.Thin-bedded silicalite generated in the interlayer of shaly slate was formed by biochemical deposit,while the silicalite with irregular lens occurrence and generated above and below the limestone layer was formed by the silicification of limestone in later period.The limestone includes sandy limestone,silicified pelletal limestone,and silicified micrite.The sandy limestone occurs in diamictic continental shelf.Silicified pelletal limstone,and silicified micrite was formed by the silicification of biogenic and biochemical silicified micrite.The slate can be divided into three types: shaly,sandy and phyllitization slate.It was formed by regional metamorphism of fine detritus in continental shelf.The macroscopic and microscopic characteristics of the three kinds of rocks indicate that the sedimentary environment of Lower Silurian in Zoige uranium ore field is continental,with alternation of the inner and outer continental shelves resulted from the growing and falling of sea level in the study area.The section structure shows a rhythm overlap of sandy slate-silty slate-micrite-shale-silicalite.