鄂尔多斯盆地北部铀矿床铀矿物赋存状态及富集机理

为了进一步深化铀矿物的富集机理.利用α径迹放射性照相、扫描电镜、电子探针等方法对鄂尔多斯盆地北部铀矿床中铀矿物的赋存状态进行了系统研究.发现该区铀矿物主要为铀石,少量沥青铀矿和含铀钛矿物.沉积-成岩期碎屑铀矿物赋存在碎屑颗粒内部,吸附在锐钛矿周围,为铀储层中预富集的铀.成矿期铀矿物大部分赋存在碎屑颗粒填隙部位,与黄铁矿、碳质碎屑相伴生,与石英颗粒及方解石胶结关系密切;部分吸附在包裹碎屑颗粒的蒙脱石薄膜上.另外发现了,沥青铀矿-赤铁矿-黄铁矿的矿物组合,以及硒铅矿(PbSe)和白硒铁矿(FeSe2)与铀矿物相伴生,并伴有REE含量明显升高.分析得出,沥青铀矿形成于成矿早期,氧化酸性流体与还原碱性流体的过渡界面,偏向于氧化酸性一侧;而铀石主要形成于成矿晚期的还原碱性环境.双重铀源供给、丰富的还原介质、多源流体的耦合,局部的热液流体叠加改造,共同造就了鄂尔多斯盆地北部大矿、富矿的形成.

Occurrence and Enrichment Mechanism of Uranium Ore Minerals from Sandstone-Type Uranium Deposit,Northern Ordos Basin

To gain new insights into metallogenic processes and especially into uranium ore minerals enrichment mechanism, occurrence of uranium ore minerals in uranium deposits of northern Ordos basin, has been analyzed using various analytical techniques including α track radiograph, scanning electron microscope (SEM) and electron microprobe (EMP). It is found that the uranium ore minerals mainly consist of coffinite, a small amount of pitchblende and uranium-bearing titanium mineral in the study area. Primary uranium ore minerals / detrital uranium minerals occur within the lithic fragment, adsorbed on anatase during the sedimentary / diagenetic stage, becoming the pre-enrichment uranium for the uranium reservoir. During the metallogenic stage, uranium ore minerals occur dominantly in the intergranular pores, associated with pyrite and carbonaceous fragments, related to quartz grains and calcite cementation closely, and a small part of which are adsorbed on montmorillonite film coating clastic particles. Besides, pitchblende - hematite - pyrite mineral assemblages, clausthalite (PbSe) and ferroselite (FeSe₂) co-existing with uranium ore minerals with high concentration of REEs, are recognized. Comprehensive analyses indicate that pitchblende is formed at the transitional interface between oxidizing acid fluid and reducing alkaline fluid, favoring the oxidizing acid side during the early metallogenic stage, and coffinite is mainly formed in the reducing alkaline conditions during the late metallogenic stage. The supply of dual uranium sources, abundant reductant, coupling of multi-source fluids, and partial superimposed transformation by hydrothermal fluid have resulted in the formation of large and rich uranium deposits in northern Ordos basin.