鄂尔多斯盆地东北部砂岩型铀矿伴生矿物组合及其地质意义

特征矿物是地质作用的直接记录,研究铀矿物伴生组合类型和特征为探讨铀矿床成因提供直接信息.本文以鄂尔多斯盆地东北部杭锦旗-纳岭沟地区含铀岩系中侏罗统直罗组为研究对象,通过岩心观察、显微观察、扫描电镜和电子探针分析等,系统研究了含铀砂岩中铀矿物种类、赋存特征及典型矿物伴生组合类型,在此基础上,结合铀成矿过程中流体作用探讨了...

Associated Mineral Assemblage of Sandstone-type Uranium Deposit in the Northeastern Ordos Basin and its Geological Significance

The typical diagnostic minerals are direct records of geological processes.The types and characteristics of minerals associated with uranium minerals may provide direct information concerning the genesis of the deposits.Here we report a case study on the uranium-bearing rock series in the Hangjinqi-Nalinggou area.Through core observation,microscopic observation,scanning electron microscopy and electron probe analysis,the uranium mineral types,occurrence characteristics and typical mineral assemblage were systematically investigated,combining with the fluid features,the mechanism of uranium mineralization is discussed.The main conclusions can be summarized as follows:(1)The main mineral type in the study area is coffinite.The mineral assemblages associated with uranium enrichment include 9 types:framboidal pyrite-coffinite,biotite-xenomorphic pyrite-coffinite,colloidal pyrite-coffinite,ilmenite-anatasecoffinite,kaolinite-coffinite,montmorillonite/montmorillonite-illite mixed layer-coffinite,calcite-coffinite,organic mattercoffinite and quartz-coffinite.(2)The ore-forming environment varied from neutral-weakly alkaline oxidation→weakly acidic oxidation→weakly acidic oxidation in the early stage;weakly alkaline reduction environment in the middle and late stage;and alkaline reduction in the post-mineralization stage.(3)Uranium enrichment can be divided into 5 stages:①pre-enrichment of detrital uranium minerals;②pitchblende enrichment at the edge of quartz particles;③coffinite precipitation at the edge of the colloidal pyrite,framboidal pyrite,anatase and kaolinite under acidic reducing environment;④coffinite precipitated from alkaline reducing fluids and associated wiht quartz,calcite and montmorillonite/montmorilloniteillite mixed layer;⑤coffinite modified by medium-low temperature hydrothermal fluids and associated with framboidal pyrite,colloidal pyrite and calcite.In summary,the main mineralization in the study area was controlled by both acidic reducing and alkaline reducing fluids.